diff --git a/.gitmodules b/.gitmodules
index bcd125a49..666a87687 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,6 +1,7 @@
 [submodule "third_party/benchmark"]
 	path = third_party/benchmark
 	url = https://github.com/google/benchmark.git
+        ignore = dirty
 [submodule "third_party/googletest"]
 	path = third_party/googletest
 	url = https://github.com/google/googletest.git
diff --git a/BUILD.bazel b/BUILD.bazel
index 98584b604..96d973c0d 100644
--- a/BUILD.bazel
+++ b/BUILD.bazel
@@ -5,7 +5,7 @@ load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library", "cc_proto_library", "c
 load("@rules_pkg//:mappings.bzl", "pkg_files", "strip_prefix")
 load("@rules_proto//proto:defs.bzl", "proto_lang_toolchain", "proto_library")
 load("@rules_java//java:defs.bzl", "java_binary", "java_lite_proto_library", "java_proto_library")
-load("//build_defs:cpp_opts.bzl", "COPTS", "LINK_OPTS")
+load("//build_defs:cpp_opts.bzl", "COPTS", "LINK_OPTS", "PROTOC_LINK_OPTS")
 load(":protobuf.bzl", "py_proto_library")
 
 licenses(["notice"])
@@ -128,13 +128,30 @@ cc_library(
     visibility = ["//visibility:public"],
 )
 
+# Source protos that are typically part of the protobuf runtime.
+#
+# DEPRECATED: Prefer :well_known_type_protos for the Well-Known Types
+# (https://developers.google.com/protocol-buffers/docs/reference/google.protobuf)
+# or :descriptor_proto(_srcs) for descriptor.proto (source), or
+# :compiler_plugin_proto for compiler/plugin.proto.
+filegroup(
+    name = "well_known_protos",
+    srcs = [
+        ":descriptor_proto_srcs",
+        ":well_known_type_protos",
+        "//src/google/protobuf/compiler:plugin.proto",
+    ],
+    deprecation = "Prefer :well_known_type_protos instead.",
+    visibility = ["//visibility:public"],
+)
+
 ################################################################################
 # Protocol Buffers Compiler
 ################################################################################
 
 cc_binary(
     name = "protoc",
-    linkopts = LINK_OPTS,
+    linkopts = LINK_OPTS + PROTOC_LINK_OPTS,
     visibility = ["//visibility:public"],
     deps = ["//src/google/protobuf/compiler:protoc_lib"],
 )
diff --git a/CMakeLists.txt b/CMakeLists.txt
index dd8977843..04cb3303a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -162,15 +162,6 @@ file(REMOVE ${CMAKE_CURRENT_BINARY_DIR}/cmaketest.map)
 
 find_package(Threads REQUIRED)
 
-# We can install dependencies from submodules if we're running
-# CMake v3.13 or newer.
-if(CMAKE_VERSION VERSION_LESS 3.13)
-  set(_protobuf_INSTALL_SUPPORTED_FROM_MODULE OFF)
-else()
-  set(_protobuf_INSTALL_SUPPORTED_FROM_MODULE ON)
-endif()
-
-
 set(_protobuf_FIND_ZLIB)
 if (protobuf_WITH_ZLIB)
   find_package(ZLIB)
@@ -313,10 +304,6 @@ if (protobuf_UNICODE)
   add_definitions(-DUNICODE -D_UNICODE)
 endif (protobuf_UNICODE)
 
-set(protobuf_ABSL_PROVIDER "module" CACHE STRING "Provider of absl library")
-set_property(CACHE protobuf_ABSL_PROVIDER PROPERTY STRINGS "module" "package")
-
-include(${protobuf_SOURCE_DIR}/cmake/abseil-cpp.cmake)
 include(${protobuf_SOURCE_DIR}/cmake/libprotobuf-lite.cmake)
 include(${protobuf_SOURCE_DIR}/cmake/libprotobuf.cmake)
 if (protobuf_BUILD_LIBPROTOC)
diff --git a/Makefile.am b/Makefile.am
index 7f064294b..9491780a4 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1214,7 +1214,6 @@ EXTRA_DIST = $(@DIST_LANG@_EXTRA_DIST)              \
   build_files_updated_unittest.sh                   \
   cmake/CMakeLists.txt                              \
   cmake/README.md                                   \
-  cmake/abseil-cpp.cmake                            \
   cmake/conformance.cmake                           \
   cmake/examples.cmake                              \
   cmake/extract_includes.bat.in                     \
diff --git a/Protobuf-C++.podspec b/Protobuf-C++.podspec
index 9d8815a8c..68571e14b 100644
--- a/Protobuf-C++.podspec
+++ b/Protobuf-C++.podspec
@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name     = 'Protobuf-C++'
-  s.version  = '3.21.0-rc1'
+  s.version  = '3.21.1'
   s.summary  = 'Protocol Buffers v3 runtime library for C++.'
   s.homepage = 'https://github.com/google/protobuf'
   s.license  = 'BSD-3-Clause'
@@ -35,6 +35,7 @@ Pod::Spec.new do |s|
     # Do not let src/google/protobuf/stubs/time.h override system API
     'USE_HEADERMAP' => 'NO',
     'ALWAYS_SEARCH_USER_PATHS' => 'NO',
+    'HEADER_SEARCH_PATHS' => '"$(PODS_TARGET_SRCROOT)/src"'
   }
 
 end
diff --git a/build_defs/BUILD.bazel b/build_defs/BUILD.bazel
index 29a1f1256..a5d831c9a 100644
--- a/build_defs/BUILD.bazel
+++ b/build_defs/BUILD.bazel
@@ -59,6 +59,20 @@ config_setting(
     },
 )
 
+config_setting(
+    name = "config_win32",
+    values = {
+        "cpu": "win32",
+    },
+)
+
+config_setting(
+    name = "config_win64",
+    values = {
+        "cpu": "win64",
+    },
+)
+
 # Internal testing:
 
 starlark_cc_proto_library(
diff --git a/build_defs/cpp_opts.bzl b/build_defs/cpp_opts.bzl
index 94966e3af..f21b861c0 100644
--- a/build_defs/cpp_opts.bzl
+++ b/build_defs/cpp_opts.bzl
@@ -38,3 +38,10 @@ LINK_OPTS = select({
         "-lm",
     ],
 })
+
+# When cross-compiling for Windows we need to statically link pthread and the C++ library.
+PROTOC_LINK_OPTS = select({
+    "//build_defs:config_win32": ["-static"],
+    "//build_defs:config_win64": ["-static"],
+    "//conditions:default": [],
+})
diff --git a/cmake/install.cmake b/cmake/install.cmake
index c1f6f4aab..825cb25fc 100644
--- a/cmake/install.cmake
+++ b/cmake/install.cmake
@@ -128,20 +128,24 @@ configure_file(${protobuf_SOURCE_DIR}/cmake/protobuf-options.cmake
 if (protobuf_BUILD_PROTOC_BINARIES)
   export(TARGETS libprotobuf-lite libprotobuf libprotoc protoc
     NAMESPACE protobuf::
-    FILE ${CMAKE_CURRENT_BINARY_DIR}/cmake/protobuf/protobuf-targets.cmake
+    FILE ${CMAKE_INSTALL_CMAKEDIR}/protobuf-targets.cmake
   )
 else (protobuf_BUILD_PROTOC_BINARIES)
   export(TARGETS libprotobuf-lite libprotobuf
     NAMESPACE protobuf::
-    FILE ${CMAKE_CURRENT_BINARY_DIR}/cmake/protobuf/protobuf-targets.cmake
+    FILE ${CMAKE_INSTALL_CMAKEDIR}/protobuf-targets.cmake
   )
 endif (protobuf_BUILD_PROTOC_BINARIES)
 
 install(EXPORT protobuf-targets
-  FILE protobuf-targets.cmake
   DESTINATION "${CMAKE_INSTALL_CMAKEDIR}"
   NAMESPACE protobuf::
+  COMPONENT protobuf-export)
+
+install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_INSTALL_CMAKEDIR}/
+  DESTINATION "${CMAKE_INSTALL_CMAKEDIR}"
   COMPONENT protobuf-export
+  PATTERN protobuf-targets.cmake EXCLUDE
 )
 
 option(protobuf_INSTALL_EXAMPLES "Install the examples folder" OFF)
diff --git a/cmake/protobuf-config.cmake.in b/cmake/protobuf-config.cmake.in
index 597f58860..67b8bf00f 100644
--- a/cmake/protobuf-config.cmake.in
+++ b/cmake/protobuf-config.cmake.in
@@ -3,7 +3,6 @@ include("${CMAKE_CURRENT_LIST_DIR}/protobuf-options.cmake")
 
 # Depend packages
 @_protobuf_FIND_ZLIB@
-@_protobuf_FIND_ABSL@
 
 # Imported targets
 include("${CMAKE_CURRENT_LIST_DIR}/protobuf-targets.cmake")
@@ -12,7 +11,7 @@ function(protobuf_generate)
   include(CMakeParseArguments)
 
   set(_options APPEND_PATH)
-  set(_singleargs LANGUAGE OUT_VAR EXPORT_MACRO PROTOC_OUT_DIR PLUGIN PLUGIN_OPTIONS)
+  set(_singleargs LANGUAGE OUT_VAR EXPORT_MACRO PROTOC_OUT_DIR PLUGIN PLUGIN_OPTIONS DEPENDENCIES)
   if(COMMAND target_sources)
     list(APPEND _singleargs TARGET)
   endif()
@@ -149,7 +148,7 @@ function(protobuf_generate)
       OUTPUT ${_generated_srcs}
       COMMAND protobuf::protoc
       ARGS ${protobuf_generate_PROTOC_OPTIONS} --${protobuf_generate_LANGUAGE}_out ${_plugin_options}:${protobuf_generate_PROTOC_OUT_DIR} ${_plugin} ${_protobuf_include_path} ${_abs_file}
-      DEPENDS ${_abs_file} protobuf::protoc
+      DEPENDS ${_abs_file} protobuf::protoc ${protobuf_generate_DEPENDENCIES}
       COMMENT ${_comment}
       VERBATIM )
   endforeach()
diff --git a/cmake/protoc.cmake b/cmake/protoc.cmake
index 385a7a3f3..472b6421b 100644
--- a/cmake/protoc.cmake
+++ b/cmake/protoc.cmake
@@ -6,7 +6,6 @@ add_executable(protoc ${protoc_files} ${protobuf_version_rc_file})
 target_link_libraries(protoc
   libprotoc
   libprotobuf
-  ${protobuf_ABSL_USED_TARGETS}
 )
 add_executable(protobuf::protoc ALIAS protoc)
 
diff --git a/configure.ac b/configure.ac
index 61246b27b..55e606478 100644
--- a/configure.ac
+++ b/configure.ac
@@ -17,7 +17,7 @@ AC_PREREQ(2.59)
 # In the SVN trunk, the version should always be the next anticipated release
 # version with the "-pre" suffix.  (We used to use "-SNAPSHOT" but this pushed
 # the size of one file name in the dist tarfile over the 99-char limit.)
-AC_INIT([Protocol Buffers],[3.21.0-rc-2],[protobuf@googlegroups.com],[protobuf])
+AC_INIT([Protocol Buffers],[3.21.1],[protobuf@googlegroups.com],[protobuf])
 
 AM_MAINTAINER_MODE([enable])
 
diff --git a/java/core/src/main/java/com/google/protobuf/ByteString.java b/java/core/src/main/java/com/google/protobuf/ByteString.java
index 480f85fd6..f13a94523 100644
--- a/java/core/src/main/java/com/google/protobuf/ByteString.java
+++ b/java/core/src/main/java/com/google/protobuf/ByteString.java
@@ -385,8 +385,7 @@ public abstract class ByteString implements Iterable<Byte>, Serializable {
   // String -> ByteString
 
   /**
-   * Returns a {@code ByteString} from a hexadecimal String. Alternative CharSequences should use
-   * {@link ByteStrings#decode(CharSequence, BaseEncoding)}
+   * Returns a {@code ByteString} from a hexadecimal String.
    *
    * @param hexString String of hexadecimal digits to create {@code ByteString} from.
    * @throws NumberFormatException if the hexString does not contain a parsable hex String.
diff --git a/kokoro/release/python/linux/build_artifacts.sh b/kokoro/release/python/linux/build_artifacts.sh
deleted file mode 100755
index 9a3fc5841..000000000
--- a/kokoro/release/python/linux/build_artifacts.sh
+++ /dev/null
@@ -1,90 +0,0 @@
-#!/bin/bash
-
-set -ex
-
-# change to repo root
-pushd $(dirname $0)/../../../..
-
-# Create stage dir
-ORIGINAL_DIR=`pwd`
-pushd ..
-cp -R $ORIGINAL_DIR stage
-export STAGE_DIR="`pwd`/stage"
-popd
-
-export REPO_DIR=protobuf
-export BUILD_VERSION=`grep -i "version" python/google/protobuf/__init__.py | grep -o "'.*'" | tr -d "'"`
-
-export BUILD_COMMIT=`git rev-parse HEAD`
-export PLAT=x86_64
-export UNICODE_WIDTH=32
-export MACOSX_DEPLOYMENT_TARGET=10.9
-
-rm -rf artifacts/
-rm -rf multibuild/
-mkdir artifacts
-export ARTIFACT_DIR=$(pwd)/artifacts
-
-git clone https://github.com/matthew-brett/multibuild.git
-# Pin multibuild scripts at a known commit to avoid potentially unwanted future changes from
-# silently creeping in (see https://github.com/protocolbuffers/protobuf/issues/9180).
-# IMPORTANT: always pin multibuild at the same commit for:
-# - linux/build_artifacts.sh
-# - linux/build_artifacts.sh
-# - windows/build_artifacts.bat
-(cd multibuild; git checkout b89bb903e94308be79abefa4f436bf123ebb1313)
-cp kokoro/release/python/linux/config.sh config.sh
-
-build_artifact_version() {
-  MB_PYTHON_VERSION=$1
-  cp -R $STAGE_DIR $REPO_DIR
-
-  source multibuild/common_utils.sh
-  source multibuild/travis_steps.sh
-  before_install
-
-  clean_code $REPO_DIR $BUILD_COMMIT
-
-  build_wheel $REPO_DIR/python $PLAT
-
-  mv wheelhouse/* $ARTIFACT_DIR
-
-  # Clean up env
-  rm -rf venv
-  sudo rm -rf $REPO_DIR
-}
-
-build_x86_64_manylinux1_artifact_version() {
-  # Explicitly request building manylinux1 wheels, which is no longer the default.
-  # https://github.com/protocolbuffers/protobuf/issues/9180
-  MB_ML_VER=1
-  build_artifact_version $@
-}
-
-build_x86_64_manylinux2010_artifact_version() {
-  # Explicitly request building manylinux2010 wheels
-  MB_ML_VER=2010
-  build_artifact_version $@
-}
-
-build_crosscompiled_aarch64_manylinux2014_artifact_version() {
-  # crosscompilation is only supported with the dockcross manylinux2014 image
-  DOCKER_IMAGE=dockcross/manylinux2014-aarch64:20210706-65bf2dd
-  MB_ML_VER=2014
-  PLAT=aarch64
-
-  # TODO(jtatermusch): currently when crosscompiling, "auditwheel repair" will be disabled
-  # since auditwheel doesn't work for crosscomiled wheels.
-  build_artifact_version $@
-}
-
-build_x86_64_manylinux1_artifact_version 3.6
-build_x86_64_manylinux1_artifact_version 3.7
-build_x86_64_manylinux1_artifact_version 3.8
-build_x86_64_manylinux1_artifact_version 3.9
-build_x86_64_manylinux2010_artifact_version 3.10
-
-build_crosscompiled_aarch64_manylinux2014_artifact_version 3.7
-build_crosscompiled_aarch64_manylinux2014_artifact_version 3.8
-build_crosscompiled_aarch64_manylinux2014_artifact_version 3.9
-build_crosscompiled_aarch64_manylinux2014_artifact_version 3.10
diff --git a/kokoro/release/python/linux/config.sh b/kokoro/release/python/linux/config.sh
deleted file mode 100644
index 892049556..000000000
--- a/kokoro/release/python/linux/config.sh
+++ /dev/null
@@ -1,93 +0,0 @@
-# Define custom utilities
-# Test for OSX with [ -n "$IS_OSX" ]
-
-function pre_build {
-    # Any stuff that you need to do before you start building the wheels
-    # Runs in the root directory of this repository.
-    pushd protobuf
-
-    if [ "$PLAT" == "aarch64" ]
-    then
-      local configure_host_flag="--host=aarch64"
-    fi
-
-    # Build protoc and libprotobuf
-    ./autogen.sh
-    CXXFLAGS="-fPIC -g -O2" ./configure $configure_host_flag
-    make -j8
-
-    if [ "$PLAT" == "aarch64" ]
-    then
-      # we are crosscompiling for aarch64 while running on x64
-      # the simplest way for build_py command to be able to generate
-      # the protos is by running the protoc process under
-      # an emulator. That way we don't have to build a x64 version
-      # of protoc. The qemu-arm emulator is already included
-      # in the dockcross docker image.
-      # Running protoc under an emulator is fast as protoc doesn't
-      # really do much.
-
-      # create a simple shell wrapper that runs crosscompiled protoc under qemu
-      echo '#!/bin/bash' >protoc_qemu_wrapper.sh
-      echo 'exec qemu-aarch64 "../src/protoc" "$@"' >>protoc_qemu_wrapper.sh
-      chmod ugo+x protoc_qemu_wrapper.sh
-
-      # PROTOC variable is by build_py step that runs under ./python directory
-      export PROTOC=../protoc_qemu_wrapper.sh
-    fi
-
-    # Generate python dependencies.
-    pushd python
-    python setup.py build_py
-    popd
-
-    popd
-}
-
-function bdist_wheel_cmd {
-    # Builds wheel with bdist_wheel, puts into wheelhouse
-    #
-    # It may sometimes be useful to use bdist_wheel for the wheel building
-    # process.  For example, versioneer has problems with versions which are
-    # fixed with bdist_wheel:
-    # https://github.com/warner/python-versioneer/issues/121
-    local abs_wheelhouse=$1
-
-    # Modify build version
-    pwd
-    ls
-
-    if [ "$PLAT" == "aarch64" ]
-    then
-      # when crosscompiling for aarch64, --plat-name needs to be set explicitly
-      # to end up with correctly named wheel file
-      # the value should be manylinuxABC_ARCH and dockcross docker image
-      # conveniently provides the value in the AUDITWHEEL_PLAT env
-      local plat_name_flag="--plat-name=$AUDITWHEEL_PLAT"
-
-      # override the value of EXT_SUFFIX to make sure the crosscompiled .so files in the wheel have the correct filename suffix
-      export PROTOCOL_BUFFERS_OVERRIDE_EXT_SUFFIX="$(python -c 'import sysconfig; print(sysconfig.get_config_var("EXT_SUFFIX").replace("-x86_64-linux-gnu.so", "-aarch64-linux-gnu.so"))')"
-    fi
-
-    python setup.py bdist_wheel --cpp_implementation --compile_static_extension $plat_name_flag
-    cp dist/*.whl $abs_wheelhouse
-}
-
-function build_wheel {
-    build_wheel_cmd "bdist_wheel_cmd" $@
-}
-
-function run_tests {
-    # Runs tests on installed distribution from an empty directory
-    python --version
-    python -c "from google.protobuf.pyext import _message;"
-}
-
-if [ "$PLAT" == "aarch64" ]
-then
-  # when crosscompiling for aarch64, override the default multibuild's repair_wheelhouse logic
-  # since "auditwheel repair" doesn't work for crosscompiled wheels
-  function repair_wheelhouse {
-      echo "Skipping repair_wheelhouse since auditwheel requires build architecture to match wheel architecture."
-  }
-fi
diff --git a/kokoro/release/python/linux/continuous.cfg b/kokoro/release/python/linux/continuous.cfg
deleted file mode 100644
index c0b9a018f..000000000
--- a/kokoro/release/python/linux/continuous.cfg
+++ /dev/null
@@ -1,8 +0,0 @@
-# Config file for running tests in Kokoro
-build_file: "protobuf/kokoro/release/python/linux/build_artifacts.sh"
-
-action {
-  define_artifacts {
-    regex: "github/protobuf/artifacts/**"
-  }
-}
diff --git a/kokoro/release/python/linux/presubmit.cfg b/kokoro/release/python/linux/presubmit.cfg
deleted file mode 100644
index c0b9a018f..000000000
--- a/kokoro/release/python/linux/presubmit.cfg
+++ /dev/null
@@ -1,8 +0,0 @@
-# Config file for running tests in Kokoro
-build_file: "protobuf/kokoro/release/python/linux/build_artifacts.sh"
-
-action {
-  define_artifacts {
-    regex: "github/protobuf/artifacts/**"
-  }
-}
diff --git a/kokoro/release/python/linux/release.cfg b/kokoro/release/python/linux/release.cfg
deleted file mode 100644
index b31b3f119..000000000
--- a/kokoro/release/python/linux/release.cfg
+++ /dev/null
@@ -1,8 +0,0 @@
-# Configuration for Linux release builds
-build_file: "protobuf/kokoro/release/python/linux/build_artifacts.sh"
-
-action {
-  define_artifacts {
-    regex: "github/protobuf/artifacts/**"
-  }
-}
diff --git a/kokoro/release/python/macos/build_artifacts.sh b/kokoro/release/python/macos/build_artifacts.sh
deleted file mode 100755
index aeb4242a6..000000000
--- a/kokoro/release/python/macos/build_artifacts.sh
+++ /dev/null
@@ -1,65 +0,0 @@
-#!/bin/bash
-
-set -ex
-
-# change to repo root
-pushd $(dirname $0)/../../../..
-
-# Create stage dir
-ORIGINAL_DIR=`pwd`
-pushd ..
-cp -R $ORIGINAL_DIR stage
-export STAGE_DIR="`pwd`/stage"
-popd
-
-export REPO_DIR=protobuf
-export BUILD_VERSION=`grep -i "version" python/google/protobuf/__init__.py | grep -o "'.*'" | tr -d "'"`
-export BUILD_COMMIT=`git rev-parse HEAD`
-export PLAT=x86_64
-export UNICODE_WIDTH=32
-export MACOSX_DEPLOYMENT_TARGET=10.9
-export TRAVIS_OS_NAME="osx"
-
-rm -rf artifacts/
-rm -rf multibuild/
-mkdir artifacts
-export ARTIFACT_DIR=$(pwd)/artifacts
-
-git clone https://github.com/matthew-brett/multibuild.git
-# Pin multibuild scripts at a known commit to avoid potentially unwanted future changes from
-# silently creeping in (see https://github.com/protocolbuffers/protobuf/issues/9180).
-# IMPORTANT: always pin multibuild at the same commit for:
-# - linux/build_artifacts.sh
-# - linux/build_artifacts.sh
-# - windows/build_artifacts.bat
-(cd multibuild; git checkout b89bb903e94308be79abefa4f436bf123ebb1313)
-cp kokoro/release/python/macos/config.sh config.sh
-
-OLD_PATH=$PATH
-
-build_artifact_version() {
-  MB_PYTHON_VERSION=$1
-
-  # Clean up env
-  rm -rf venv
-  sudo rm -rf $REPO_DIR
-  cp -R $STAGE_DIR $REPO_DIR
-  export PATH=$OLD_PATH
-
-  source multibuild/common_utils.sh
-  source multibuild/travis_steps.sh
-  before_install
-
-  clean_code $REPO_DIR $BUILD_COMMIT
-
-  build_wheel $REPO_DIR/python $PLAT
-
-  mv wheelhouse/* $ARTIFACT_DIR
-}
-
-export MB_PYTHON_OSX_VER=10.9
-build_artifact_version 3.6
-build_artifact_version 3.7
-build_artifact_version 3.8
-build_artifact_version 3.9
-build_artifact_version 3.10
diff --git a/kokoro/release/python/macos/config.sh b/kokoro/release/python/macos/config.sh
deleted file mode 100644
index 250c76bc0..000000000
--- a/kokoro/release/python/macos/config.sh
+++ /dev/null
@@ -1,68 +0,0 @@
-# Define custom utilities
-# Test for OSX with [ -n "$IS_OSX" ]
-
-function remove_travis_ve_pip {
-    # Removing the system virtualenv or pip can be very problematic for
-    # macOS on Kokoro, so just leave them be.
-    :;
-}
-
-function install_pip {
-    check_python
-    PIP_CMD="sudo $PYTHON_EXE -m pip${pip_args:+ $pip_args}"
-    $PIP_CMD install --upgrade pip
-}
-
-function install_virtualenv {
-    check_python
-    check_pip
-    $PIP_CMD install --upgrade virtualenv
-    VIRTUALENV_CMD="$PYTHON_EXE -m virtualenv"
-}
-
-function pre_build {
-    # Any stuff that you need to do before you start building the wheels
-    # Runs in the root directory of this repository.
-    pushd protobuf
-
-    # Build protoc and protobuf libraries
-    use_bazel.sh 5.1.1
-    bazel build -c opt //:protoc //pkg:protobuf //pkg:protobuf_lite
-    local _bazel_bin=$(bazel info -c opt bazel-bin)
-    export PROTOC=${_bazel_bin}/protoc
-    export LIBPROTOBUF=${_bazel_bin}/pkg/libprotobuf.a
-
-    # Generate python dependencies.
-    pushd python
-    python setup.py build_py
-    popd
-
-    popd
-}
-
-function bdist_wheel_cmd {
-    # Builds wheel with bdist_wheel, puts into wheelhouse
-    #
-    # It may sometimes be useful to use bdist_wheel for the wheel building
-    # process.  For example, versioneer has problems with versions which are
-    # fixed with bdist_wheel:
-    # https://github.com/warner/python-versioneer/issues/121
-    local abs_wheelhouse=$1
-
-    # Modify build version
-    pwd
-    ls
-    python setup.py build_ext --cpp_implementation -O${LIBPROTOBUF}
-    python setup.py bdist_wheel --cpp_implementation
-    cp dist/*.whl $abs_wheelhouse
-}
-
-function build_wheel {
-    build_wheel_cmd "bdist_wheel_cmd" $@
-}
-
-function run_tests {
-    # Runs tests on installed distribution from an empty directory
-    python --version
-    python -c "from google.protobuf.pyext import _message;"
-}
diff --git a/kokoro/release/python/macos/continuous.cfg b/kokoro/release/python/macos/continuous.cfg
deleted file mode 100644
index 85cf81b50..000000000
--- a/kokoro/release/python/macos/continuous.cfg
+++ /dev/null
@@ -1,8 +0,0 @@
-# Configuration for Mac OSX release builds
-build_file: "protobuf/kokoro/release/python/macos/build_artifacts.sh"
-
-action {
-  define_artifacts {
-    regex: "github/protobuf/artifacts/**"
-  }
-}
diff --git a/kokoro/release/python/macos/presubmit.cfg b/kokoro/release/python/macos/presubmit.cfg
deleted file mode 100644
index 85cf81b50..000000000
--- a/kokoro/release/python/macos/presubmit.cfg
+++ /dev/null
@@ -1,8 +0,0 @@
-# Configuration for Mac OSX release builds
-build_file: "protobuf/kokoro/release/python/macos/build_artifacts.sh"
-
-action {
-  define_artifacts {
-    regex: "github/protobuf/artifacts/**"
-  }
-}
diff --git a/kokoro/release/python/macos/release.cfg b/kokoro/release/python/macos/release.cfg
deleted file mode 100644
index 85cf81b50..000000000
--- a/kokoro/release/python/macos/release.cfg
+++ /dev/null
@@ -1,8 +0,0 @@
-# Configuration for Mac OSX release builds
-build_file: "protobuf/kokoro/release/python/macos/build_artifacts.sh"
-
-action {
-  define_artifacts {
-    regex: "github/protobuf/artifacts/**"
-  }
-}
diff --git a/kokoro/release/python/windows/build_artifacts.bat b/kokoro/release/python/windows/build_artifacts.bat
deleted file mode 100644
index 121283a43..000000000
--- a/kokoro/release/python/windows/build_artifacts.bat
+++ /dev/null
@@ -1,88 +0,0 @@
-REM Move scripts to root
-set REPO_DIR_STAGE=%cd%\github\protobuf-stage
-xcopy /S  github\protobuf "%REPO_DIR_STAGE%\"
-cd github\protobuf
-copy kokoro\release\python\windows\build_single_artifact.bat build_single_artifact.bat
-
-REM Set environment variables
-set PACKAGE_NAME=protobuf
-set REPO_DIR=protobuf
-set BUILD_DLL=OFF
-set UNICODE=ON
-set OTHER_TEST_DEP="setuptools==38.5.1"
-set OLD_PATH=C:\Program Files (x86)\MSBuild\14.0\bin\;%PATH%
-
-REM Fetch multibuild
-git clone https://github.com/matthew-brett/multibuild.git
-REM Pin multibuild scripts at a known commit to avoid potentially unwanted future changes from
-REM silently creeping in (see https://github.com/protocolbuffers/protobuf/issues/9180).
-REM IMPORTANT: always pin multibuild at the same commit for:
-REM - linux/build_artifacts.sh
-REM - linux/build_artifacts.sh
-REM - windows/build_artifacts.bat
-cd multibuild
-git checkout b89bb903e94308be79abefa4f436bf123ebb1313
-cd ..
-
-REM Install zlib
-mkdir zlib
-curl -L -o zlib.zip http://www.winimage.com/zLibDll/zlib123dll.zip
-curl -L -o zlib-src.zip http://www.winimage.com/zLibDll/zlib123.zip
-7z x zlib.zip -ozlib
-7z x zlib-src.zip -ozlib\include
-SET ZLIB_ROOT=%cd%\zlib
-del /Q zlib.zip
-del /Q zlib-src.zip
-
-REM Create directory for artifacts
-SET ARTIFACT_DIR=%cd%\artifacts
-mkdir %ARTIFACT_DIR%
-
-REM Build wheel
-
-SET PYTHON=C:\python37_32bit
-SET PYTHON_VERSION=3.7
-SET PYTHON_ARCH=32
-CALL build_single_artifact.bat || goto :error
-
-SET PYTHON=C:\python37
-SET PYTHON_VERSION=3.7
-SET PYTHON_ARCH=64
-CALL build_single_artifact.bat || goto :error
-
-powershell -File kokoro/release/python/windows/install_python_interpreters.ps1
-
-SET PYTHON=C:\python38_32bit
-SET PYTHON_VERSION=3.8
-SET PYTHON_ARCH=32
-CALL build_single_artifact.bat || goto :error
-
-SET PYTHON=C:\python38
-SET PYTHON_VERSION=3.8
-SET PYTHON_ARCH=64
-CALL build_single_artifact.bat || goto :error
-
-SET PYTHON=C:\python39_32bit
-SET PYTHON_VERSION=3.9
-SET PYTHON_ARCH=32
-CALL build_single_artifact.bat || goto :error
-
-SET PYTHON=C:\python39
-SET PYTHON_VERSION=3.9
-SET PYTHON_ARCH=64
-CALL build_single_artifact.bat || goto :error
-
-SET PYTHON=C:\python310_32bit
-SET PYTHON_VERSION=3.10
-SET PYTHON_ARCH=32
-CALL build_single_artifact.bat || goto :error
-
-SET PYTHON=C:\python310
-SET PYTHON_VERSION=3.10
-SET PYTHON_ARCH=64
-CALL build_single_artifact.bat || goto :error
-
-goto :EOF
-
-:error
-exit /b %errorlevel%
diff --git a/kokoro/release/python/windows/build_single_artifact.bat b/kokoro/release/python/windows/build_single_artifact.bat
deleted file mode 100644
index af2d26526..000000000
--- a/kokoro/release/python/windows/build_single_artifact.bat
+++ /dev/null
@@ -1,78 +0,0 @@
-setlocal
-
-if %PYTHON%==C:\python37_32bit set generator=Visual Studio 14
-if %PYTHON%==C:\python37_32bit set vcplatform=Win32
-
-if %PYTHON%==C:\python37 set generator=Visual Studio 14 Win64
-if %PYTHON%==C:\python37 set vcplatform=x64
-
-if %PYTHON%==C:\python38_32bit set generator=Visual Studio 14
-if %PYTHON%==C:\python38_32bit set vcplatform=Win32
-
-if %PYTHON%==C:\python38 set generator=Visual Studio 14 Win64
-if %PYTHON%==C:\python38 set vcplatform=x64
-
-if %PYTHON%==C:\python39_32bit set generator=Visual Studio 14
-if %PYTHON%==C:\python39_32bit set vcplatform=Win32
-
-if %PYTHON%==C:\python39 set generator=Visual Studio 14 Win64
-if %PYTHON%==C:\python39 set vcplatform=x64
-
-if %PYTHON%==C:\python310_32bit set generator=Visual Studio 14
-if %PYTHON%==C:\python310_32bit set vcplatform=Win32
-
-if %PYTHON%==C:\python310 set generator=Visual Studio 14 Win64
-if %PYTHON%==C:\python310 set vcplatform=x64
-
-REM Prepend newly installed Python to the PATH of this build (this cannot be
-REM done from inside the powershell script as it would require to restart
-REM the parent CMD process).
-SET PATH=C:\Program Files\CMake\bin;%PYTHON%;%PYTHON%\Scripts;%OLD_PATH%
-python -m pip install -U pip
-pip install wheel
-
-REM Check that we have the expected version and architecture for Python
-python --version
-python -c "import struct; print(struct.calcsize('P') * 8)"
-
-rmdir /s/q %REPO_DIR%
-xcopy /s  %REPO_DIR_STAGE% "%REPO_DIR%\"
-
-REM Checkout release commit
-cd %REPO_DIR%
-
-REM ======================
-REM Build Protobuf Library
-REM ======================
-
-mkdir src\.libs
-
-mkdir vcprojects
-pushd vcprojects
-cmake -G "%generator%" -Dprotobuf_BUILD_SHARED_LIBS=%BUILD_DLL% -Dprotobuf_UNICODE=%UNICODE% -Dprotobuf_BUILD_TESTS=OFF ../cmake || goto :error
-msbuild protobuf.sln /p:Platform=%vcplatform% /p:Configuration=Release || goto :error
-dir /s /b
-popd
-copy vcprojects\Release\libprotobuf.lib src\.libs\libprotobuf.a
-copy vcprojects\Release\libprotobuf-lite.lib src\.libs\libprotobuf-lite.a
-SET PATH=%cd%\vcprojects\Release;%PATH%
-dir vcprojects\Release
-
-REM ======================
-REM Build python library
-REM ======================
-
-cd python
-
-REM sed -i 's/\ extra_compile_args\ =\ \[\]/\ extra_compile_args\ =\ \[\'\/MT\'\]/g' setup.py
-
-python setup.py bdist_wheel --cpp_implementation --compile_static_extension
-dir dist
-copy dist\* %ARTIFACT_DIR%
-dir %ARTIFACT_DIR%
-cd ..\..
-
-goto :EOF
-
-:error
-exit /b %errorlevel%
diff --git a/kokoro/release/python/windows/continuous.cfg b/kokoro/release/python/windows/continuous.cfg
deleted file mode 100644
index 526160647..000000000
--- a/kokoro/release/python/windows/continuous.cfg
+++ /dev/null
@@ -1,8 +0,0 @@
-# Configuration for Windows protoc release builds
-build_file: "protobuf/kokoro/release/python/windows/build_artifacts.bat"
-
-action {
-  define_artifacts {
-    regex: "github/protobuf/artifacts/**"
-  }
-}
diff --git a/kokoro/release/python/windows/install_python_interpreters.ps1 b/kokoro/release/python/windows/install_python_interpreters.ps1
deleted file mode 100644
index 3f8db95b7..000000000
--- a/kokoro/release/python/windows/install_python_interpreters.ps1
+++ /dev/null
@@ -1,114 +0,0 @@
-#!/usr/bin/env powershell
-# Install Python 3.8 for x64 and x86 in order to build wheels on Windows.
-# Originally from grpc/tools/internal_ci/helper_scripts/install_python_interpreters.ps1
-
-Set-StrictMode -Version 2
-$ErrorActionPreference = 'Stop'
-
-trap {
-    $ErrorActionPreference = "Continue"
-    Write-Error $_
-    exit 1
-}
-
-# Avoid "Could not create SSL/TLS secure channel"
-[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
-
-function Install-Python {
-    Param(
-        [string]$PythonVersion,
-        [string]$PythonInstaller,
-        [string]$PythonInstallPath,
-        [string]$PythonInstallerHash
-    )
-    $PythonInstallerUrl = "https://www.python.org/ftp/python/$PythonVersion/$PythonInstaller.exe"
-    $PythonInstallerPath = "C:\tools\$PythonInstaller.exe"
-
-    # Downloads installer
-    Write-Host "Downloading the Python installer: $PythonInstallerUrl => $PythonInstallerPath"
-    Invoke-WebRequest -Uri $PythonInstallerUrl -OutFile $PythonInstallerPath
-
-    # Validates checksum
-    $HashFromDownload = Get-FileHash -Path $PythonInstallerPath -Algorithm MD5
-    if ($HashFromDownload.Hash -ne $PythonInstallerHash) {
-        throw "Invalid Python installer: failed checksum!"
-    }
-    Write-Host "Python installer $PythonInstallerPath validated."
-
-    # Installs Python
-    & $PythonInstallerPath /passive InstallAllUsers=1 PrependPath=1 Include_test=0 TargetDir=$PythonInstallPath
-    if (-Not $?) {
-        throw "The Python installation exited with error!"
-    }
-
-    # NOTE(lidiz) Even if the install command finishes in the script, that
-    # doesn't mean the Python installation is finished. If using "ps" to check
-    # for running processes, you might see ongoing installers at this point.
-    # So, we needs this "hack" to reliably validate that the Python binary is
-    # functioning properly.
-
-    # Wait for the installer process
-    Wait-Process -Name $PythonInstaller -Timeout 300
-    Write-Host "Installation process exits normally."
-
-    # Validate Python binary
-    $PythonBinary = "$PythonInstallPath\python.exe"
-    & $PythonBinary -c 'print(42)'
-    Write-Host "Python binary works properly."
-
-    # Installs pip
-    & $PythonBinary -m ensurepip --user
-
-    Write-Host "Python $PythonVersion installed by $PythonInstaller at $PythonInstallPath."
-}
-
-# Python 3.8
-$Python38x86Config = @{
-    PythonVersion = "3.8.0"
-    PythonInstaller = "python-3.8.0"
-    PythonInstallPath = "C:\python38_32bit"
-    PythonInstallerHash = "412a649d36626d33b8ca5593cf18318c"
-}
-Install-Python @Python38x86Config
-
-$Python38x64Config = @{
-    PythonVersion = "3.8.0"
-    PythonInstaller = "python-3.8.0-amd64"
-    PythonInstallPath = "C:\python38"
-    PythonInstallerHash = "29ea87f24c32f5e924b7d63f8a08ee8d"
-}
-Install-Python @Python38x64Config
-
-# Python 3.9
-$Python39x86Config = @{
-    PythonVersion = "3.9.0"
-    PythonInstaller = "python-3.9.0"
-    PythonInstallPath = "C:\python39_32bit"
-    PythonInstallerHash = "4a2812db8ab9f2e522c96c7728cfcccb"
-}
-Install-Python @Python39x86Config
-
-$Python39x64Config = @{
-    PythonVersion = "3.9.0"
-    PythonInstaller = "python-3.9.0-amd64"
-    PythonInstallPath = "C:\python39"
-    PythonInstallerHash = "b61a33dc28f13b561452f3089c87eb63"
-}
-Install-Python @Python39x64Config
-
-# Python 3.10
-$Python310x86Config = @{
-    PythonVersion = "3.10.0"
-    PythonInstaller = "python-3.10.0"
-    PythonInstallPath = "C:\python310_32bit"
-    PythonInstallerHash = "133aa48145032e341ad2a000cd3bff50"
-}
-Install-Python @Python310x86Config
-
-$Python310x64Config = @{
-    PythonVersion = "3.10.0"
-    PythonInstaller = "python-3.10.0-amd64"
-    PythonInstallPath = "C:\python310"
-    PythonInstallerHash = "c3917c08a7fe85db7203da6dcaa99a70"
-}
-Install-Python @Python310x64Config
diff --git a/kokoro/release/python/windows/presubmit.cfg b/kokoro/release/python/windows/presubmit.cfg
deleted file mode 100644
index 526160647..000000000
--- a/kokoro/release/python/windows/presubmit.cfg
+++ /dev/null
@@ -1,8 +0,0 @@
-# Configuration for Windows protoc release builds
-build_file: "protobuf/kokoro/release/python/windows/build_artifacts.bat"
-
-action {
-  define_artifacts {
-    regex: "github/protobuf/artifacts/**"
-  }
-}
diff --git a/kokoro/release/python/windows/release.cfg b/kokoro/release/python/windows/release.cfg
deleted file mode 100644
index 526160647..000000000
--- a/kokoro/release/python/windows/release.cfg
+++ /dev/null
@@ -1,8 +0,0 @@
-# Configuration for Windows protoc release builds
-build_file: "protobuf/kokoro/release/python/windows/build_artifacts.bat"
-
-action {
-  define_artifacts {
-    regex: "github/protobuf/artifacts/**"
-  }
-}
diff --git a/pkg/BUILD.bazel b/pkg/BUILD.bazel
index a2663dc2b..2a310963f 100644
--- a/pkg/BUILD.bazel
+++ b/pkg/BUILD.bazel
@@ -27,7 +27,7 @@ pkg_files(
 pkg_files(
     name = "compiler_plugin_protos_files",
     srcs = [
-      "//src/google/protobuf/compiler:compiler_plugin_protos_files",
+        "//src/google/protobuf/compiler:compiler_plugin_protos_files",
     ],
     prefix = "include/google/protobuf/compiler",
     visibility = ["//visibility:private"],
@@ -304,10 +304,33 @@ gen_file_lists(
     testonly = 1,
     out_stem = "src_file_lists",
     src_libs = {
-        # source rule: name in generated file
+        # {[source rule]: [name in generated file]}
+        # Libraries:
         ":protobuf": "libprotobuf",
-        ":protoc": "libprotoc",
         ":protobuf_lite": "libprotobuf_lite",
+        ":protoc": "libprotoc",
+        # Protos:
+        "//src/google/protobuf:well_known_type_protos": "wkt_protos",
+        "//src/google/protobuf:descriptor_proto": "descriptor_proto",
+        "//src/google/protobuf/compiler:plugin_proto": "plugin_proto",
+        # Test libraries:
+        ":lite_test_util": "lite_test_util",
+        ":test_util": "test_util",
+        # Tests and test-only protos:
+        "//src/google/protobuf:full_test_srcs": "protobuf_test",
+        "//src/google/protobuf:test_protos": "protobuf_test_protos",
+        "//src/google/protobuf:lite_test_srcs": "protobuf_lite_test",
+        "//src/google/protobuf:lite_test_protos": "protobuf_lite_test_protos",
+        "//src/google/protobuf/compiler:test_srcs": "compiler_test",
+        ":compiler_annotation_test_util": "annotation_test_util",
+        ":compiler_mock_code_generator": "mock_code_generator",
+        "//src/google/protobuf/compiler:test_proto_srcs": "compiler_test_protos",
+        "//src/google/protobuf/compiler:test_plugin_srcs": "test_plugin",
+        "//src/google/protobuf/io:test_srcs": "io_test",
+        ":testinglib": "testing",
+        "//src/google/protobuf/util:test_srcs": "util_test",
+        "//src/google/protobuf/util:test_proto_srcs": "util_test_protos",
+        "//src/google/protobuf/stubs:test_srcs": "stubs_test",
     },
 )
 
@@ -362,15 +385,15 @@ cc_dist_library(
     }),
     tags = ["manual"],
     deps = [
+        "//src/google/protobuf",
         "//src/google/protobuf:arena",
+        "//src/google/protobuf:protobuf_lite",
         "//src/google/protobuf/compiler:importer",
         "//src/google/protobuf/io",
         "//src/google/protobuf/io:gzip_stream",
         "//src/google/protobuf/io:io_win32",
         "//src/google/protobuf/io:printer",
         "//src/google/protobuf/io:tokenizer",
-        "//src/google/protobuf:protobuf",
-        "//src/google/protobuf:protobuf_lite",
         "//src/google/protobuf/stubs",
         "//src/google/protobuf/stubs:lite",
         "//src/google/protobuf/util:delimited_message_util",
@@ -379,6 +402,14 @@ cc_dist_library(
         "//src/google/protobuf/util:json_util",
         "//src/google/protobuf/util:time_util",
         "//src/google/protobuf/util:type_resolver_util",
+        "//src/google/protobuf/util/internal:datapiece",
+        "//src/google/protobuf/util/internal:default_value",
+        "//src/google/protobuf/util/internal:field_mask_utility",
+        "//src/google/protobuf/util/internal:json",
+        "//src/google/protobuf/util/internal:object_writer",
+        "//src/google/protobuf/util/internal:protostream",
+        "//src/google/protobuf/util/internal:type_info",
+        "//src/google/protobuf/util/internal:utility",
     ],
 )
 
@@ -398,6 +429,41 @@ cc_dist_library(
     ],
 )
 
+cc_dist_library(
+    name = "lite_test_util",
+    testonly = 1,
+    tags = ["manual"],
+    deps = ["//src/google/protobuf:lite_test_util"],
+)
+
+cc_dist_library(
+    name = "test_util",
+    testonly = 1,
+    tags = ["manual"],
+    deps = ["//src/google/protobuf:test_util"],
+)
+
+cc_dist_library(
+    name = "compiler_annotation_test_util",
+    deps = ["//src/google/protobuf/compiler:annotation_test_util"],
+    testonly = 1,
+    tags = ["manual"],
+)
+
+cc_dist_library(
+    name = "compiler_mock_code_generator",
+    deps = ["//src/google/protobuf/compiler:mock_code_generator"],
+    testonly = 1,
+    tags = ["manual"],
+)
+
+cc_dist_library(
+    name = "testinglib",
+    deps = ["//src/google/protobuf/testing"],
+    testonly = 1,
+    tags = ["manual"],
+)
+
 ################################################################################
 # Distribution sources
 ################################################################################
diff --git a/python/google/protobuf/__init__.py b/python/google/protobuf/__init__.py
index bd2faa4e5..56781369c 100644
--- a/python/google/protobuf/__init__.py
+++ b/python/google/protobuf/__init__.py
@@ -30,4 +30,4 @@
 
 # Copyright 2007 Google Inc. All Rights Reserved.
 
-__version__ = '4.21.0rc2'
+__version__ = '4.21.1'
diff --git a/src/google/protobuf/BUILD.bazel b/src/google/protobuf/BUILD.bazel
index a8736c337..0f0fd4df6 100644
--- a/src/google/protobuf/BUILD.bazel
+++ b/src/google/protobuf/BUILD.bazel
@@ -87,6 +87,10 @@ proto_library(
     name = "descriptor_proto",
     srcs = ["descriptor.proto"],
     strip_import_prefix = "/src",
+    visibility = [
+        "//:__pkg__",
+        "//pkg:__pkg__",
+    ],
 )
 
 ################################################################################
@@ -146,10 +150,35 @@ cc_library(
         "repeated_ptr_field.cc",
         "wire_format_lite.cc",
     ],
-    hdrs = glob([
-        "**/*.h",
-        "**/*.inc",
-    ]),
+    hdrs = [
+        "any.h",
+        "arena.h",
+        "arena_impl.h",
+        "arenastring.h",
+        "arenaz_sampler.h",
+        "endian.h",
+        "explicitly_constructed.h",
+        "extension_set.h",
+        "extension_set_inl.h",
+        "generated_enum_util.h",
+        "generated_message_tctable_decl.h",
+        "generated_message_tctable_impl.h",
+        "generated_message_util.h",
+        "has_bits.h",
+        "implicit_weak_message.h",
+        "inlined_string_field.h",
+        "map.h",
+        "map_entry_lite.h",
+        "map_field_lite.h",
+        "map_type_handler.h",
+        "message_lite.h",
+        "metadata_lite.h",
+        "parse_context.h",
+        "port.h",
+        "repeated_field.h",
+        "repeated_ptr_field.h",
+        "wire_format_lite.h",
+    ],
     copts = COPTS + select({
         "//build_defs:config_msvc": [],
         "//conditions:default": [
@@ -201,10 +230,38 @@ cc_library(
         "wire_format.cc",
         "wrappers.pb.cc",
     ],
-    hdrs = glob([
-        "**/*.h",
-        "**/*.inc",
-    ]),
+    hdrs = [
+        "any.pb.h",
+        "api.pb.h",
+        "descriptor.h",
+        "descriptor.pb.h",
+        "descriptor_database.h",
+        "duration.pb.h",
+        "dynamic_message.h",
+        "empty.pb.h",
+        "field_access_listener.h",
+        "field_mask.pb.h",
+        "generated_enum_reflection.h",
+        "generated_message_bases.h",
+        "generated_message_reflection.h",
+        "map_entry.h",
+        "map_field.h",
+        "map_field_inl.h",
+        "message.h",
+        "metadata.h",
+        "reflection.h",
+        "reflection_internal.h",
+        "reflection_ops.h",
+        "service.h",
+        "source_context.pb.h",
+        "struct.pb.h",
+        "text_format.h",
+        "timestamp.pb.h",
+        "type.pb.h",
+        "unknown_field_set.h",
+        "wire_format.h",
+        "wrappers.pb.h",
+    ],
     copts = COPTS,
     include_prefix = "google/protobuf",
     linkopts = LINK_OPTS,
@@ -442,24 +499,47 @@ filegroup(
 )
 
 cc_library(
-    name = "test_util",
+    name = "lite_test_util",
     testonly = 1,
     srcs = [
         "arena_test_util.cc",
         "map_lite_test_util.cc",
-        "reflection_tester.cc",
-        "test_util.cc",
         "test_util_lite.cc",
     ],
     hdrs = [
         "arena_test_util.h",
         "map_lite_test_util.h",
-        "map_test_util.h",
         "map_test_util_impl.h",
-        "test_util.h",
-        "test_util2.h",
+        "proto3_lite_unittest.inc",
         "test_util_lite.h",
     ],
+    strip_include_prefix = "/src",
+    visibility = ["//:__subpackages__"],
+    deps = [
+        ":cc_lite_test_protos",
+        ":test_util2",
+        "@com_google_googletest//:gtest",
+    ],
+)
+
+cc_library(
+    name = "test_util",
+    testonly = 1,
+    srcs = [
+        "reflection_tester.cc",
+        "test_util.cc",
+    ],
+    hdrs = [
+        "map_test.inc",
+        "map_test_util.h",
+        "map_test_util.inc",
+        "message_unittest.inc",
+        "reflection_tester.h",
+        "test_util.h",
+        "test_util.inc",
+        "test_util_lite.h",
+        "wire_format_unittest.inc",
+    ],
     copts = COPTS + select({
         "//build_defs:config_msvc": [],
         "//conditions:default": [
@@ -467,76 +547,524 @@ cc_library(
         ],
     }),
     strip_include_prefix = "/src",
-    textual_hdrs = [
-        "map_test_util.inc",
-        "test_util.inc",
-    ],
     visibility = ["//:__subpackages__"],
     deps = [
         ":cc_lite_test_protos",
         ":cc_test_protos",
+        ":lite_test_util",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+    ],
+)
+
+cc_library(
+    name = "test_util2",
+    testonly = 1,
+    hdrs = ["test_util2.h"],
+    strip_include_prefix = "/src",
+    textual_hdrs = ["test_util.inc"],
+    visibility = ["//:__subpackages__"],
+    deps = [
+        "//src/google/protobuf/io",
         "@com_google_googletest//:gtest",
     ],
 )
 
 cc_test(
-    name = "protobuf_test",
-    srcs = [
-        "any_test.cc",
-        "arena_unittest.cc",
-        "arenastring_unittest.cc",
-        "arenaz_sampler_test.cc",
-        "descriptor_database_unittest.cc",
-        "descriptor_unittest.cc",
-        "drop_unknown_fields_test.cc",
-        "dynamic_message_unittest.cc",
-        "extension_set_unittest.cc",
-        "generated_message_reflection_unittest.cc",
-        "generated_message_tctable_lite_test.cc",
-        "inlined_string_field_unittest.cc",
-        "map_field_test.cc",
-        "map_test.cc",
-        "map_test.inc",
-        "message_unittest.cc",
-        "message_unittest.inc",
-        "no_field_presence_test.cc",
-        "preserve_unknown_enum_test.cc",
-        "proto3_arena_lite_unittest.cc",
-        "proto3_arena_unittest.cc",
-        "proto3_lite_unittest.cc",
-        "proto3_lite_unittest.inc",
-        "reflection_ops_unittest.cc",
-        "repeated_field_reflection_unittest.cc",
-        "repeated_field_unittest.cc",
-        "text_format_unittest.cc",
-        "unknown_field_set_unittest.cc",
-        "well_known_types_unittest.cc",
-        "wire_format_unittest.cc",
-        "wire_format_unittest.inc",
+    name = "any_test",
+    srcs = ["any_test.cc"],
+    deps = [
+        ":protobuf",
+        ":test_util",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
     ],
+)
+
+cc_test(
+    name = "arena_unittest",
+    srcs = ["arena_unittest.cc"],
     copts = COPTS + select({
         "//build_defs:config_msvc": [],
         "//conditions:default": [
-            "-Wno-deprecated-declarations",
             "-Wno-error=sign-compare",
         ],
     }),
-    data = [
-        ":testdata",
-    ] + glob([
-        "**/*",
-    ]),
-    linkopts = LINK_OPTS,
     deps = [
-        ":cc_lite_test_protos",
         ":cc_test_protos",
+        ":lite_test_util",
         ":protobuf",
         ":test_util",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "arenastring_unittest",
+    srcs = ["arenastring_unittest.cc"],
+    deps = [
+        ":protobuf",
+        "//src/google/protobuf/io",
+        "//src/google/protobuf/stubs",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "arenaz_sampler_test",
+    srcs = ["arenaz_sampler_test.cc"],
+    deps = [
+        ":protobuf",
+        "//src/google/protobuf/stubs",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "descriptor_database_unittest",
+    srcs = ["descriptor_database_unittest.cc"],
+    deps = [
+        ":protobuf",
         "//src/google/protobuf/testing",
         "@com_google_googletest//:gtest",
         "@com_google_googletest//:gtest_main",
     ],
 )
+
+cc_test(
+    name = "descriptor_unittest",
+    srcs = ["descriptor_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-error=sign-compare",
+        ],
+    }),
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        "//src/google/protobuf/compiler:importer",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "drop_unknown_fields_test",
+    srcs = ["drop_unknown_fields_test.cc"],
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "dynamic_message_unittest",
+    srcs = ["dynamic_message_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-error=sign-compare",
+        ],
+    }),
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        ":test_util",
+        "//src/google/protobuf/stubs",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "extension_set_unittest",
+    srcs = ["extension_set_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-error=sign-compare",
+        ],
+    }),
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        ":test_util",
+        "//src/google/protobuf/io",
+        "//src/google/protobuf/stubs",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "generated_message_reflection_unittest",
+    srcs = ["generated_message_reflection_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-error=sign-compare",
+        ],
+    }),
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        ":test_util",
+        "//src/google/protobuf/stubs",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "generated_message_tctable_lite_test",
+    srcs = ["generated_message_tctable_lite_test.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-error=sign-compare",
+        ],
+    }),
+    deps = [
+        ":protobuf_lite",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "inlined_string_field_unittest",
+    srcs = ["inlined_string_field_unittest.cc"],
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        "//src/google/protobuf/io",
+        "//src/google/protobuf/stubs",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "lite_arena_unittest",
+    srcs = ["lite_arena_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-error=sign-compare",
+        ],
+    }),
+    deps = [
+        ":lite_test_util",
+        ":protobuf",
+        ":test_util",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "lite_unittest",
+    srcs = ["lite_unittest.cc"],
+    deps = [
+        ":cc_lite_test_protos",
+        ":lite_test_util",
+        ":protobuf",
+        "//src/google/protobuf/io",
+        "//src/google/protobuf/stubs",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "map_field_test",
+    srcs = ["map_field_test.cc"],
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        ":test_util",
+        "//src/google/protobuf/stubs",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "map_test",
+    srcs = [
+        "map_test.cc",
+        "map_test.inc",
+    ],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-deprecated-declarations",
+        ],
+    }),
+    data = [":testdata"],
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        ":test_util",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "message_unittest",
+    srcs = [
+        "message_unittest.cc",
+        "message_unittest.inc",
+    ],
+    data = [":testdata"],
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        ":test_util",
+        "//src/google/protobuf/io",
+        "//src/google/protobuf/stubs",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "no_field_presence_test",
+    srcs = ["no_field_presence_test.cc"],
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "preserve_unknown_enum_test",
+    srcs = ["preserve_unknown_enum_test.cc"],
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "proto3_arena_lite_unittest",
+    srcs = ["proto3_arena_lite_unittest.cc"],
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "proto3_arena_unittest",
+    srcs = ["proto3_arena_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-error=sign-compare",
+        ],
+    }),
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        ":test_util",
+        "//src/google/protobuf/stubs",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "proto3_lite_unittest",
+    srcs = [
+        "proto3_lite_unittest.cc",
+        "proto3_lite_unittest.inc",
+    ],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-deprecated-declarations",
+        ],
+    }),
+    deps = [
+        ":cc_test_protos",
+        ":lite_test_util",
+        ":protobuf",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "reflection_ops_unittest",
+    srcs = ["reflection_ops_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-error=sign-compare",
+        ],
+    }),
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        ":test_util",
+        "//src/google/protobuf/stubs",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "repeated_field_reflection_unittest",
+    srcs = ["repeated_field_reflection_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-deprecated-declarations",
+        ],
+    }),
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        ":test_util",
+        "//src/google/protobuf/stubs",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "repeated_field_unittest",
+    srcs = ["repeated_field_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-deprecated-declarations",
+        ],
+    }),
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        "//src/google/protobuf/stubs",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "text_format_unittest",
+    srcs = ["text_format_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-deprecated-declarations",
+        ],
+    }),
+    data = [":testdata"],
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        ":test_util",
+        "//src/google/protobuf/io",
+        "//src/google/protobuf/stubs",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "unknown_field_set_unittest",
+    srcs = ["unknown_field_set_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-error=sign-compare",
+        ],
+    }),
+    deps = [
+        ":cc_lite_test_protos",
+        ":protobuf",
+        ":test_util",
+        "//src/google/protobuf/io",
+        "//src/google/protobuf/stubs",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "well_known_types_unittest",
+    srcs = ["well_known_types_unittest.cc"],
+    copts = COPTS + select({
+        "//build_defs:config_msvc": [],
+        "//conditions:default": [
+            "-Wno-deprecated-declarations",
+        ],
+    }),
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        "//src/google/protobuf/stubs",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "wire_format_unittest",
+    srcs = [
+        "wire_format_unittest.cc",
+        "wire_format_unittest.inc",
+    ],
+    deps = [
+        ":cc_test_protos",
+        ":protobuf",
+        ":test_util",
+        ":test_util2",
+        "//src/google/protobuf/io",
+        "//src/google/protobuf/stubs",
+        "//src/google/protobuf/testing",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+# Legacy target: all test sources used to be part of this rule. It is
+# still kept around for now.
+cc_test(
+    name = "protobuf_test",
+    srcs = [],
+    deps = [
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 ################################################################################
 # Helper targets for Kotlin tests
 ################################################################################
@@ -577,3 +1105,27 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "full_test_srcs",
+    srcs = glob(
+        include = [
+            "*_test.cc",
+            "*unittest.cc",
+        ],
+        exclude = [
+            "lite_unittest.cc",
+            "lite_arena_unittest.cc",
+        ],
+    ),
+    visibility = ["//pkg:__pkg__"],
+)
+
+filegroup(
+    name = "lite_test_srcs",
+    srcs = [
+        "lite_arena_unittest.cc",
+        "lite_unittest.cc",
+    ],
+    visibility = ["//pkg:__pkg__"],
+)
diff --git a/src/google/protobuf/any.pb.cc b/src/google/protobuf/any.pb.cc
index c02f9eb7f..379991e24 100644
--- a/src/google/protobuf/any.pb.cc
+++ b/src/google/protobuf/any.pb.cc
@@ -52,6 +52,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fany_2eproto::offsets[] PROTOBUF_S
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Any, _impl_.type_url_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Any, _impl_.value_),
 };
diff --git a/src/google/protobuf/any.pb.h b/src/google/protobuf/any.pb.h
index b3b4e6a16..6db2ab3d3 100644
--- a/src/google/protobuf/any.pb.h
+++ b/src/google/protobuf/any.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/api.pb.cc b/src/google/protobuf/api.pb.cc
index 24b60497c..24e118eeb 100644
--- a/src/google/protobuf/api.pb.cc
+++ b/src/google/protobuf/api.pb.cc
@@ -85,6 +85,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fapi_2eproto::offsets[] PROTOBUF_S
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Api, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Api, _impl_.methods_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Api, _impl_.options_),
@@ -98,6 +100,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fapi_2eproto::offsets[] PROTOBUF_S
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Method, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Method, _impl_.request_type_url_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Method, _impl_.request_streaming_),
@@ -111,13 +115,15 @@ const uint32_t TableStruct_google_2fprotobuf_2fapi_2eproto::offsets[] PROTOBUF_S
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Mixin, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Mixin, _impl_.root_),
 };
 static const ::_pbi::MigrationSchema schemas[] PROTOBUF_SECTION_VARIABLE(protodesc_cold) = {
   { 0, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Api)},
-  { 13, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Method)},
-  { 26, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Mixin)},
+  { 15, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Method)},
+  { 30, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Mixin)},
 };
 
 static const ::_pb::Message* const file_default_instances[] = {
diff --git a/src/google/protobuf/api.pb.h b/src/google/protobuf/api.pb.h
index 2f7d90516..a06f93012 100644
--- a/src/google/protobuf/api.pb.h
+++ b/src/google/protobuf/api.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/arenastring.cc b/src/google/protobuf/arenastring.cc
index d886ddad6..4dce6df08 100644
--- a/src/google/protobuf/arenastring.cc
+++ b/src/google/protobuf/arenastring.cc
@@ -86,7 +86,7 @@ const std::string& LazyString::Init() const {
 namespace {
 
 
-#if defined(NDEBUG) || !GOOGLE_PROTOBUF_INTERNAL_DONATE_STEAL
+#if defined(NDEBUG) || !defined(GOOGLE_PROTOBUF_INTERNAL_DONATE_STEAL)
 
 class ScopedCheckPtrInvariants {
  public:
@@ -102,7 +102,7 @@ inline TaggedStringPtr CreateString(ConstStringParam value) {
   return res;
 }
 
-#if !GOOGLE_PROTOBUF_INTERNAL_DONATE_STEAL
+#ifndef GOOGLE_PROTOBUF_INTERNAL_DONATE_STEAL
 
 // Creates an arena allocated std::string value.
 TaggedStringPtr CreateArenaString(Arena& arena, ConstStringParam s) {
@@ -123,7 +123,17 @@ void ArenaStringPtr::Set(ConstStringParam value, Arena* arena) {
     tagged_ptr_ = arena != nullptr ? CreateArenaString(*arena, value)
                                    : CreateString(value);
   } else {
+#ifdef PROTOBUF_FORCE_COPY_DEFAULT_STRING
+    if (arena == nullptr) {
+      Destroy();
+      tagged_ptr_ = CreateString(value);
+    } else {
+      UnsafeMutablePointer()->assign("garbagedata");
+      tagged_ptr_ = CreateArenaString(*arena, value);
+    }
+#else   // PROTOBUF_FORCE_COPY_DEFAULT_STRING
     UnsafeMutablePointer()->assign(value.data(), value.length());
+#endif  // PROTOBUF_FORCE_COPY_DEFAULT_STRING
   }
 }
 
diff --git a/src/google/protobuf/compiler/BUILD.bazel b/src/google/protobuf/compiler/BUILD.bazel
index 8da74f10a..419e8f5a1 100644
--- a/src/google/protobuf/compiler/BUILD.bazel
+++ b/src/google/protobuf/compiler/BUILD.bazel
@@ -16,7 +16,10 @@ load("//build_defs:cpp_opts.bzl", "COPTS")
 proto_library(
     name = "plugin_proto",
     srcs = ["plugin.proto"],
-    visibility = ["//:__pkg__"],
+    visibility = [
+        "//:__pkg__",
+        "//pkg:__pkg__",
+    ],
     deps = ["//:descriptor_proto"],
 )
 
@@ -150,6 +153,11 @@ filegroup(
     ],
 )
 
+exports_files(
+    srcs = ["plugin.proto"],
+    visibility = ["//:__pkg__"],
+)
+
 cc_library(
     name = "mock_code_generator",
     testonly = 1,
@@ -157,6 +165,7 @@ cc_library(
     hdrs = ["mock_code_generator.h"],
     copts = COPTS,
     strip_include_prefix = "/src",
+    visibility = ["//pkg:__pkg__"],
     deps = [
         ":code_generator",
         "//src/google/protobuf/io",
@@ -199,6 +208,7 @@ cc_test(
         ":mock_code_generator",
         "//:protobuf",
         "//src/google/protobuf:cc_test_protos",
+        "//src/google/protobuf:test_util2",
         "//src/google/protobuf/io",
         "//src/google/protobuf/stubs",
         "//src/google/protobuf/testing",
@@ -236,6 +246,7 @@ cc_test(
         ":importer",
         "//:protobuf",
         "//src/google/protobuf:cc_test_protos",
+        "//src/google/protobuf:test_util2",
         "//src/google/protobuf/io",
         "//src/google/protobuf/stubs",
         "//src/google/protobuf/testing",
@@ -293,3 +304,34 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]) + [
+        "//src/google/protobuf/compiler/cpp:test_srcs",
+        "//src/google/protobuf/compiler/csharp:test_srcs",
+        "//src/google/protobuf/compiler/java:test_srcs",
+        "//src/google/protobuf/compiler/objectivec:test_srcs",
+        "//src/google/protobuf/compiler/php:test_srcs",
+        "//src/google/protobuf/compiler/python:test_srcs",
+        "//src/google/protobuf/compiler/ruby:test_srcs",
+    ],
+    visibility = ["//pkg:__pkg__"],
+)
+
+filegroup(
+    name = "test_plugin_srcs",
+    srcs = ["test_plugin.cc"],
+    visibility = ["//pkg:__pkg__"],
+)
+
+filegroup(
+    name = "test_proto_srcs",
+    srcs = [
+        "//src/google/protobuf/compiler/cpp:test_proto_srcs",
+    ],
+    visibility = ["//pkg:__pkg__"],
+)
diff --git a/src/google/protobuf/compiler/cpp/BUILD.bazel b/src/google/protobuf/compiler/cpp/BUILD.bazel
index b14259495..098fd63e8 100644
--- a/src/google/protobuf/compiler/cpp/BUILD.bazel
+++ b/src/google/protobuf/compiler/cpp/BUILD.bazel
@@ -107,6 +107,8 @@ cc_test(
         ":unittest_lib",
         "//:protobuf",
         "//src/google/protobuf:cc_test_protos",
+        "//src/google/protobuf:test_util",
+        "//src/google/protobuf:test_util2",
         "//src/google/protobuf/compiler:importer",
         "//src/google/protobuf/io",
         "//src/google/protobuf/stubs",
@@ -129,6 +131,7 @@ cc_test(
     deps = [
         ":cpp",
         "//:protobuf",
+        "//src/google/protobuf:test_util2",
         "//src/google/protobuf/compiler:importer",
         "//src/google/protobuf/io",
         "//src/google/protobuf/stubs",
@@ -199,3 +202,21 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]),
+    visibility = ["//src/google/protobuf/compiler:__pkg__"],
+)
+
+filegroup(
+    name = "test_proto_srcs",
+    srcs = [
+        "test_bad_identifiers.proto",
+        "test_large_enum_value.proto",
+    ],
+    visibility = ["//src/google/protobuf/compiler:__pkg__"],
+)
diff --git a/src/google/protobuf/compiler/cpp/field.h b/src/google/protobuf/compiler/cpp/field.h
index dd2a51a2f..3fcbda371 100644
--- a/src/google/protobuf/compiler/cpp/field.h
+++ b/src/google/protobuf/compiler/cpp/field.h
@@ -150,9 +150,6 @@ class FieldGenerator {
   // method, invoked by each of the generated constructors.
   virtual void GenerateConstructorCode(io::Printer* printer) const = 0;
 
-  // Generate initialization code for private members in the cold struct.
-  virtual void GenerateCreateSplitMessageCode(io::Printer* printer) const {}
-
   // Generate any code that needs to go in the class's SharedDtor() method,
   // invoked by the destructor.
   // Most field types don't need this, so the default implementation is empty.
diff --git a/src/google/protobuf/compiler/cpp/message.cc b/src/google/protobuf/compiler/cpp/message.cc
index d3190fabc..f4eb744e2 100644
--- a/src/google/protobuf/compiler/cpp/message.cc
+++ b/src/google/protobuf/compiler/cpp/message.cc
@@ -1986,9 +1986,6 @@ void MessageGenerator::GenerateClassDefinition(io::Printer* printer) {
   }
 
   if (ShouldSplit(descriptor_, options_)) {
-    format(
-        "static Impl_::Split* CreateSplitMessage("
-        "::$proto_ns$::Arena* arena);\n");
     format("friend struct $1$;\n",
            DefaultInstanceType(descriptor_, options_, /*split=*/true));
   }
@@ -2036,7 +2033,6 @@ void MessageGenerator::GenerateSchema(io::Printer* printer, int offset,
     GOOGLE_DCHECK(!IsMapEntryMessage(descriptor_));
     inlined_string_indices_offset = has_offset + has_bit_indices_.size();
   }
-
   format("{ $1$, $2$, $3$, sizeof($classtype$)},\n", offset, has_offset,
          inlined_string_indices_offset);
 }
@@ -2199,9 +2195,13 @@ void MessageGenerator::GenerateClassMethods(io::Printer* printer) {
     format(
         "void $classname$::PrepareSplitMessageForWrite() {\n"
         "  if (IsSplitMessageDefault()) {\n"
-        "    $split$ = CreateSplitMessage(GetArenaForAllocation());\n"
+        "    void* chunk = "
+        "::PROTOBUF_NAMESPACE_ID::internal::CreateSplitMessageGeneric("
+        "GetArenaForAllocation(), &$1$, sizeof(Impl_::Split));\n"
+        "    $split$ = reinterpret_cast<Impl_::Split*>(chunk);\n"
         "  }\n"
-        "}\n");
+        "}\n",
+        DefaultInstanceName(descriptor_, options_, /*split=*/true));
   }
 
   GenerateVerify(printer);
@@ -2276,7 +2276,16 @@ std::pair<size_t, size_t> MessageGenerator::GenerateOffsets(
   } else {
     format("~0u,  // no _inlined_string_donated_\n");
   }
-  const int kNumGenericOffsets = 6;  // the number of fixed offsets above
+  if (ShouldSplit(descriptor_, options_)) {
+    format(
+        "PROTOBUF_FIELD_OFFSET($classtype$, $split$),\n"
+        "sizeof($classtype$::Impl_::Split),\n");
+  } else {
+    format(
+        "~0u,  // no _split_\n"
+        "~0u,  // no sizeof(Split)\n");
+  }
+  const int kNumGenericOffsets = 8;  // the number of fixed offsets above
   const size_t offsets = kNumGenericOffsets + descriptor_->field_count() +
                          descriptor_->real_oneof_decl_count();
   size_t entries = offsets;
@@ -2304,12 +2313,17 @@ std::pair<size_t, size_t> MessageGenerator::GenerateOffsets(
     // offset of the field, so that the information is available when
     // reflectively accessing the field at run time.
     //
-    // Embed whether the field is eagerly verified lazy or inlined string to the
-    // LSB of the offset.
+    // We embed whether the field is cold to the MSB of the offset, and whether
+    // the field is eagerly verified lazy or inlined string to the LSB of the
+    // offset.
+
+    if (ShouldSplit(field, options_)) {
+      format(" | ::_pbi::kSplitFieldOffsetMask /*split*/");
+    }
     if (IsEagerlyVerifiedLazy(field, options_, scc_analyzer_)) {
-      format(" | 0x1u  // eagerly verified lazy\n");
+      format(" | 0x1u /*eagerly verified lazy*/");
     } else if (IsStringInlined(field, options_)) {
-      format(" | 0x1u  // inlined\n");
+      format(" | 0x1u /*inlined*/");
     }
     format(",\n");
   }
@@ -2470,45 +2484,6 @@ void MessageGenerator::GenerateSharedConstructorCode(io::Printer* printer) {
   format("}\n\n");
 }
 
-void MessageGenerator::GenerateCreateSplitMessage(io::Printer* printer) {
-  Formatter format(printer, variables_);
-  format(
-      "$classname$::Impl_::Split* "
-      "$classname$::CreateSplitMessage(::$proto_ns$::Arena* arena) {\n");
-  format.Indent();
-  const char* field_sep = " ";
-  const auto put_sep = [&] {
-    format("\n$1$ ", field_sep);
-    field_sep = ",";
-  };
-  format(
-      "const size_t size = sizeof(Impl_::Split);\n"
-      "void* chunk = (arena == nullptr) ?\n"
-      "  ::operator new(size) :\n"
-      "  arena->AllocateAligned(size, alignof(Impl_::Split));\n"
-      "Impl_::Split* ptr = reinterpret_cast<Impl_::Split*>(chunk);\n"
-      "new (ptr) Impl_::Split{");
-  format.Indent();
-  for (const FieldDescriptor* field : optimized_order_) {
-    GOOGLE_DCHECK(!IsFieldStripped(field, options_));
-    if (ShouldSplit(field, options_)) {
-      put_sep();
-      field_generators_.get(field).GenerateAggregateInitializer(printer);
-    }
-  }
-  format.Outdent();
-  format("};\n");
-  for (const FieldDescriptor* field : optimized_order_) {
-    GOOGLE_DCHECK(!IsFieldStripped(field, options_));
-    if (ShouldSplit(field, options_)) {
-      field_generators_.get(field).GenerateCreateSplitMessageCode(printer);
-    }
-  }
-  format("return ptr;\n");
-  format.Outdent();
-  format("}\n");
-}
-
 void MessageGenerator::GenerateInitDefaultSplitInstance(io::Printer* printer) {
   if (!ShouldSplit(descriptor_, options_)) return;
 
@@ -2947,10 +2922,6 @@ void MessageGenerator::GenerateStructors(io::Printer* printer) {
   // Generate the shared constructor code.
   GenerateSharedConstructorCode(printer);
 
-  if (ShouldSplit(descriptor_, options_)) {
-    GenerateCreateSplitMessage(printer);
-  }
-
   // Generate the destructor.
   if (!HasSimpleBaseClass(descriptor_, options_)) {
     format(
diff --git a/src/google/protobuf/compiler/cpp/message.h b/src/google/protobuf/compiler/cpp/message.h
index 5bdfcb35e..998ebdb24 100644
--- a/src/google/protobuf/compiler/cpp/message.h
+++ b/src/google/protobuf/compiler/cpp/message.h
@@ -119,7 +119,6 @@ class MessageGenerator {
   // default instance.
   void GenerateConstexprConstructor(io::Printer* printer);
 
-  void GenerateCreateSplitMessage(io::Printer* printer);
   void GenerateInitDefaultSplitInstance(io::Printer* printer);
 
   // Generate standard Message methods.
diff --git a/src/google/protobuf/compiler/cpp/parse_function_generator.cc b/src/google/protobuf/compiler/cpp/parse_function_generator.cc
index 91ceeeb25..3254b3758 100644
--- a/src/google/protobuf/compiler/cpp/parse_function_generator.cc
+++ b/src/google/protobuf/compiler/cpp/parse_function_generator.cc
@@ -93,7 +93,7 @@ bool IsFieldEligibleForFastParsing(
   if (field->is_map() || field->real_containing_oneof() ||
       field->options().weak() ||
       IsImplicitWeakField(field, options, scc_analyzer) ||
-      IsLazy(field, options, scc_analyzer)) {
+      IsLazy(field, options, scc_analyzer) || ShouldSplit(field, options)) {
     return false;
   }
 
@@ -313,6 +313,16 @@ TailCallTableInfo::TailCallTableInfo(
                      ", _impl_._inlined_string_donated_)}");
   }
 
+  // If this message is split, store the split pointer offset in the third
+  // auxiliary entry.
+  if (ShouldSplit(descriptor, options)) {
+    aux_entries.resize(4);  // pad if necessary
+    aux_entries[2] = StrCat("_fl::Offset{offsetof(",
+                                  ClassName(descriptor), ", _impl_._split_)}");
+    aux_entries[3] = StrCat("_fl::Offset{sizeof(", ClassName(descriptor),
+                                  "::Impl_::Split)}");
+  }
+
   // Fill in mini table entries.
   for (const FieldDescriptor* field : ordered_fields) {
     field_entries.push_back(
@@ -919,14 +929,12 @@ void ParseFunctionGenerator::GenerateFastFieldEntries(Formatter& format) {
     if (info.func_name.empty()) {
       format("{::_pbi::TcParser::MiniParse, {}},\n");
     } else {
-      bool cold = ShouldSplit(info.field, options_);
+      GOOGLE_CHECK(!ShouldSplit(info.field, options_));
       format(
           "{$1$,\n"
-          " {$2$, $3$, $4$, PROTOBUF_FIELD_OFFSET($classname$$5$, $6$)}},\n",
+          " {$2$, $3$, $4$, PROTOBUF_FIELD_OFFSET($classname$, $5$)}},\n",
           info.func_name, info.coded_tag, info.hasbit_idx, info.aux_idx,
-          cold ? "::Impl_::Split" : "",
-          cold ? FieldName(info.field) + "_"
-               : FieldMemberName(info.field, /*cold=*/false));
+          FieldMemberName(info.field, /*split=*/false));
     }
   }
 }
@@ -1067,6 +1075,10 @@ static void FormatFieldKind(Formatter& format,
     }
   }
 
+  if (ShouldSplit(field, options)) {
+    format(" | ::_fl::kSplitTrue");
+  }
+
   format(")");
 }
 
@@ -1081,11 +1093,14 @@ void ParseFunctionGenerator::GenerateFieldEntries(Formatter& format) {
       format("/* weak */ 0, 0, 0, 0");
     } else {
       const OneofDescriptor* oneof = field->real_containing_oneof();
-      bool cold = ShouldSplit(field, options_);
-      format("PROTOBUF_FIELD_OFFSET($classname$$1$, $2$), ",
-             cold ? "::Impl_::Split" : "",
-             cold ? FieldName(field) + "_"
-                  : FieldMemberName(field, /*cold=*/false));
+      bool split = ShouldSplit(field, options_);
+      if (split) {
+        format("PROTOBUF_FIELD_OFFSET($classname$::Impl_::Split, $1$), ",
+               FieldName(field) + "_");
+      } else {
+        format("PROTOBUF_FIELD_OFFSET($classname$, $1$), ",
+               FieldMemberName(field, /*cold=*/false));
+      }
       if (oneof) {
         format("$1$, ", oneof->index());
       } else if (num_hasbits_ > 0 || IsMapEntryMessage(descriptor_)) {
diff --git a/src/google/protobuf/compiler/cpp/string_field.cc b/src/google/protobuf/compiler/cpp/string_field.cc
index 9e7c96d7c..71b9b5412 100644
--- a/src/google/protobuf/compiler/cpp/string_field.cc
+++ b/src/google/protobuf/compiler/cpp/string_field.cc
@@ -445,21 +445,6 @@ void StringFieldGenerator::GenerateConstructorCode(io::Printer* printer) const {
   }
 }
 
-void StringFieldGenerator::GenerateCreateSplitMessageCode(
-    io::Printer* printer) const {
-  GOOGLE_CHECK(ShouldSplit(descriptor_, options_));
-  GOOGLE_CHECK(!inlined_);
-  Formatter format(printer, variables_);
-  format("ptr->$name$_.InitDefault();\n");
-  if (IsString(descriptor_, options_) &&
-      descriptor_->default_value_string().empty()) {
-    format(
-        "#ifdef PROTOBUF_FORCE_COPY_DEFAULT_STRING\n"
-        "  ptr->$name$_.Set(\"\", GetArenaForAllocation());\n"
-        "#endif // PROTOBUF_FORCE_COPY_DEFAULT_STRING\n");
-  }
-}
-
 void StringFieldGenerator::GenerateCopyConstructorCode(
     io::Printer* printer) const {
   Formatter format(printer, variables_);
diff --git a/src/google/protobuf/compiler/cpp/string_field.h b/src/google/protobuf/compiler/cpp/string_field.h
index db5f18bfb..b1865ea67 100644
--- a/src/google/protobuf/compiler/cpp/string_field.h
+++ b/src/google/protobuf/compiler/cpp/string_field.h
@@ -63,7 +63,6 @@ class StringFieldGenerator : public FieldGenerator {
   void GenerateMergingCode(io::Printer* printer) const override;
   void GenerateSwappingCode(io::Printer* printer) const override;
   void GenerateConstructorCode(io::Printer* printer) const override;
-  void GenerateCreateSplitMessageCode(io::Printer* printer) const override;
   void GenerateCopyConstructorCode(io::Printer* printer) const override;
   void GenerateDestructorCode(io::Printer* printer) const override;
   void GenerateArenaDestructorCode(io::Printer* printer) const override;
diff --git a/src/google/protobuf/compiler/csharp/BUILD.bazel b/src/google/protobuf/compiler/csharp/BUILD.bazel
index 819c9dec2..ca9eb350a 100644
--- a/src/google/protobuf/compiler/csharp/BUILD.bazel
+++ b/src/google/protobuf/compiler/csharp/BUILD.bazel
@@ -107,3 +107,12 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]),
+    visibility = ["//src/google/protobuf/compiler:__pkg__"],
+)
diff --git a/src/google/protobuf/compiler/java/BUILD.bazel b/src/google/protobuf/compiler/java/BUILD.bazel
index 66a809ec2..619d71518 100644
--- a/src/google/protobuf/compiler/java/BUILD.bazel
+++ b/src/google/protobuf/compiler/java/BUILD.bazel
@@ -124,3 +124,12 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]),
+    visibility = ["//src/google/protobuf/compiler:__pkg__"],
+)
diff --git a/src/google/protobuf/compiler/objectivec/BUILD.bazel b/src/google/protobuf/compiler/objectivec/BUILD.bazel
index 634dda248..30b6237a4 100644
--- a/src/google/protobuf/compiler/objectivec/BUILD.bazel
+++ b/src/google/protobuf/compiler/objectivec/BUILD.bazel
@@ -70,3 +70,12 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]),
+    visibility = ["//src/google/protobuf/compiler:__pkg__"],
+)
diff --git a/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc b/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc
index 7f7ee34c4..1c497d805 100644
--- a/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc
+++ b/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc
@@ -112,7 +112,7 @@ class PrefixModeStorage {
  public:
   PrefixModeStorage();
 
-  const std::string package_to_prefix_mappings_path() const { return package_to_prefix_mappings_path_; }
+  std::string package_to_prefix_mappings_path() const { return package_to_prefix_mappings_path_; }
   void set_package_to_prefix_mappings_path(const std::string& path) {
     package_to_prefix_mappings_path_ = path;
     package_to_prefix_map_.clear();
@@ -123,7 +123,7 @@ class PrefixModeStorage {
   bool use_package_name() const { return use_package_name_; }
   void set_use_package_name(bool on_or_off) { use_package_name_ = on_or_off; }
 
-  const std::string exception_path() const { return exception_path_; }
+  std::string exception_path() const { return exception_path_; }
   void set_exception_path(const std::string& path) {
     exception_path_ = path;
     exceptions_.clear();
diff --git a/src/google/protobuf/compiler/php/BUILD.bazel b/src/google/protobuf/compiler/php/BUILD.bazel
index 82ba185fd..2ce166b31 100644
--- a/src/google/protobuf/compiler/php/BUILD.bazel
+++ b/src/google/protobuf/compiler/php/BUILD.bazel
@@ -32,3 +32,12 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]),
+    visibility = ["//src/google/protobuf/compiler:__pkg__"],
+)
diff --git a/src/google/protobuf/compiler/plugin.pb.cc b/src/google/protobuf/compiler/plugin.pb.cc
index def353e21..32bfac19a 100644
--- a/src/google/protobuf/compiler/plugin.pb.cc
+++ b/src/google/protobuf/compiler/plugin.pb.cc
@@ -102,6 +102,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fcompiler_2fplugin_2eproto::offset
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::Version, _impl_.major_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::Version, _impl_.minor_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::Version, _impl_.patch_),
@@ -116,6 +118,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fcompiler_2fplugin_2eproto::offset
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorRequest, _impl_.file_to_generate_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorRequest, _impl_.parameter_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorRequest, _impl_.proto_file_),
@@ -130,6 +134,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fcompiler_2fplugin_2eproto::offset
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorResponse_File, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorResponse_File, _impl_.insertion_point_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorResponse_File, _impl_.content_),
@@ -144,6 +150,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fcompiler_2fplugin_2eproto::offset
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorResponse, _impl_.error_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorResponse, _impl_.supported_features_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorResponse, _impl_.file_),
@@ -152,10 +160,10 @@ const uint32_t TableStruct_google_2fprotobuf_2fcompiler_2fplugin_2eproto::offset
   ~0u,
 };
 static const ::_pbi::MigrationSchema schemas[] PROTOBUF_SECTION_VARIABLE(protodesc_cold) = {
-  { 0, 10, -1, sizeof(::PROTOBUF_NAMESPACE_ID::compiler::Version)},
-  { 14, 24, -1, sizeof(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorRequest)},
-  { 28, 38, -1, sizeof(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorResponse_File)},
-  { 42, 51, -1, sizeof(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorResponse)},
+  { 0, 12, -1, sizeof(::PROTOBUF_NAMESPACE_ID::compiler::Version)},
+  { 16, 28, -1, sizeof(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorRequest)},
+  { 32, 44, -1, sizeof(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorResponse_File)},
+  { 48, 59, -1, sizeof(::PROTOBUF_NAMESPACE_ID::compiler::CodeGeneratorResponse)},
 };
 
 static const ::_pb::Message* const file_default_instances[] = {
diff --git a/src/google/protobuf/compiler/plugin.pb.h b/src/google/protobuf/compiler/plugin.pb.h
index b8829b495..1c4b0f6c0 100644
--- a/src/google/protobuf/compiler/plugin.pb.h
+++ b/src/google/protobuf/compiler/plugin.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/compiler/python/BUILD.bazel b/src/google/protobuf/compiler/python/BUILD.bazel
index 1924a9ac5..d2d0ce12f 100644
--- a/src/google/protobuf/compiler/python/BUILD.bazel
+++ b/src/google/protobuf/compiler/python/BUILD.bazel
@@ -54,3 +54,12 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]),
+    visibility = ["//src/google/protobuf/compiler:__pkg__"],
+)
diff --git a/src/google/protobuf/compiler/ruby/BUILD.bazel b/src/google/protobuf/compiler/ruby/BUILD.bazel
index 455865322..73b0fcf96 100644
--- a/src/google/protobuf/compiler/ruby/BUILD.bazel
+++ b/src/google/protobuf/compiler/ruby/BUILD.bazel
@@ -59,3 +59,12 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]),
+    visibility = ["//src/google/protobuf/compiler:__pkg__"],
+)
diff --git a/src/google/protobuf/descriptor.pb.cc b/src/google/protobuf/descriptor.pb.cc
index 645096686..257798e4a 100644
--- a/src/google/protobuf/descriptor.pb.cc
+++ b/src/google/protobuf/descriptor.pb.cc
@@ -517,6 +517,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FileDescriptorSet, _impl_.file_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FileDescriptorProto, _impl_._has_bits_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FileDescriptorProto, _internal_metadata_),
@@ -524,6 +526,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FileDescriptorProto, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FileDescriptorProto, _impl_.package_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FileDescriptorProto, _impl_.dependency_),
@@ -554,6 +558,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::DescriptorProto_ExtensionRange, _impl_.start_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::DescriptorProto_ExtensionRange, _impl_.end_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::DescriptorProto_ExtensionRange, _impl_.options_),
@@ -566,6 +572,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::DescriptorProto_ReservedRange, _impl_.start_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::DescriptorProto_ReservedRange, _impl_.end_),
   0,
@@ -576,6 +584,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::DescriptorProto, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::DescriptorProto, _impl_.field_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::DescriptorProto, _impl_.extension_),
@@ -602,6 +612,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::ExtensionRangeOptions, _impl_.uninterpreted_option_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FieldDescriptorProto, _impl_._has_bits_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FieldDescriptorProto, _internal_metadata_),
@@ -609,6 +621,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FieldDescriptorProto, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FieldDescriptorProto, _impl_.number_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FieldDescriptorProto, _impl_.label_),
@@ -637,6 +651,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::OneofDescriptorProto, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::OneofDescriptorProto, _impl_.options_),
   0,
@@ -647,6 +663,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumDescriptorProto_EnumReservedRange, _impl_.start_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumDescriptorProto_EnumReservedRange, _impl_.end_),
   0,
@@ -657,6 +675,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumDescriptorProto, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumDescriptorProto, _impl_.value_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumDescriptorProto, _impl_.options_),
@@ -673,6 +693,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumValueDescriptorProto, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumValueDescriptorProto, _impl_.number_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumValueDescriptorProto, _impl_.options_),
@@ -685,6 +707,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::ServiceDescriptorProto, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::ServiceDescriptorProto, _impl_.method_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::ServiceDescriptorProto, _impl_.options_),
@@ -697,6 +721,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::MethodDescriptorProto, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::MethodDescriptorProto, _impl_.input_type_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::MethodDescriptorProto, _impl_.output_type_),
@@ -715,6 +741,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FileOptions, _impl_.java_package_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FileOptions, _impl_.java_outer_classname_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FileOptions, _impl_.java_multiple_files_),
@@ -763,6 +791,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::MessageOptions, _impl_.message_set_wire_format_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::MessageOptions, _impl_.no_standard_descriptor_accessor_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::MessageOptions, _impl_.deprecated_),
@@ -779,6 +809,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FieldOptions, _impl_.ctype_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FieldOptions, _impl_.packed_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FieldOptions, _impl_.jstype_),
@@ -801,6 +833,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::OneofOptions, _impl_.uninterpreted_option_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumOptions, _impl_._has_bits_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumOptions, _internal_metadata_),
@@ -808,6 +842,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumOptions, _impl_.allow_alias_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumOptions, _impl_.deprecated_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumOptions, _impl_.uninterpreted_option_),
@@ -820,6 +856,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumValueOptions, _impl_.deprecated_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumValueOptions, _impl_.uninterpreted_option_),
   0,
@@ -830,6 +868,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::ServiceOptions, _impl_.deprecated_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::ServiceOptions, _impl_.uninterpreted_option_),
   0,
@@ -840,6 +880,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::MethodOptions, _impl_.deprecated_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::MethodOptions, _impl_.idempotency_level_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::MethodOptions, _impl_.uninterpreted_option_),
@@ -852,6 +894,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::UninterpretedOption_NamePart, _impl_.name_part_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::UninterpretedOption_NamePart, _impl_.is_extension_),
   0,
@@ -862,6 +906,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::UninterpretedOption, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::UninterpretedOption, _impl_.identifier_value_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::UninterpretedOption, _impl_.positive_int_value_),
@@ -882,6 +928,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::SourceCodeInfo_Location, _impl_.path_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::SourceCodeInfo_Location, _impl_.span_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::SourceCodeInfo_Location, _impl_.leading_comments_),
@@ -898,6 +946,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::SourceCodeInfo, _impl_.location_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo_Annotation, _impl_._has_bits_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo_Annotation, _internal_metadata_),
@@ -905,6 +955,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo_Annotation, _impl_.path_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo_Annotation, _impl_.source_file_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo_Annotation, _impl_.begin_),
@@ -919,36 +971,38 @@ const uint32_t TableStruct_google_2fprotobuf_2fdescriptor_2eproto::offsets[] PRO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo, _impl_.annotation_),
 };
 static const ::_pbi::MigrationSchema schemas[] PROTOBUF_SECTION_VARIABLE(protodesc_cold) = {
   { 0, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::FileDescriptorSet)},
-  { 7, 25, -1, sizeof(::PROTOBUF_NAMESPACE_ID::FileDescriptorProto)},
-  { 37, 46, -1, sizeof(::PROTOBUF_NAMESPACE_ID::DescriptorProto_ExtensionRange)},
-  { 49, 57, -1, sizeof(::PROTOBUF_NAMESPACE_ID::DescriptorProto_ReservedRange)},
-  { 59, 75, -1, sizeof(::PROTOBUF_NAMESPACE_ID::DescriptorProto)},
-  { 85, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::ExtensionRangeOptions)},
-  { 92, 109, -1, sizeof(::PROTOBUF_NAMESPACE_ID::FieldDescriptorProto)},
-  { 120, 128, -1, sizeof(::PROTOBUF_NAMESPACE_ID::OneofDescriptorProto)},
-  { 130, 138, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumDescriptorProto_EnumReservedRange)},
-  { 140, 151, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumDescriptorProto)},
-  { 156, 165, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumValueDescriptorProto)},
-  { 168, 177, -1, sizeof(::PROTOBUF_NAMESPACE_ID::ServiceDescriptorProto)},
-  { 180, 192, -1, sizeof(::PROTOBUF_NAMESPACE_ID::MethodDescriptorProto)},
-  { 198, 225, -1, sizeof(::PROTOBUF_NAMESPACE_ID::FileOptions)},
-  { 246, 257, -1, sizeof(::PROTOBUF_NAMESPACE_ID::MessageOptions)},
-  { 262, 276, -1, sizeof(::PROTOBUF_NAMESPACE_ID::FieldOptions)},
-  { 284, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::OneofOptions)},
-  { 291, 300, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumOptions)},
-  { 303, 311, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumValueOptions)},
-  { 313, 321, -1, sizeof(::PROTOBUF_NAMESPACE_ID::ServiceOptions)},
-  { 323, 332, -1, sizeof(::PROTOBUF_NAMESPACE_ID::MethodOptions)},
-  { 335, 343, -1, sizeof(::PROTOBUF_NAMESPACE_ID::UninterpretedOption_NamePart)},
-  { 345, 358, -1, sizeof(::PROTOBUF_NAMESPACE_ID::UninterpretedOption)},
-  { 365, 376, -1, sizeof(::PROTOBUF_NAMESPACE_ID::SourceCodeInfo_Location)},
-  { 381, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::SourceCodeInfo)},
-  { 388, 398, -1, sizeof(::PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo_Annotation)},
-  { 402, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo)},
+  { 9, 29, -1, sizeof(::PROTOBUF_NAMESPACE_ID::FileDescriptorProto)},
+  { 41, 52, -1, sizeof(::PROTOBUF_NAMESPACE_ID::DescriptorProto_ExtensionRange)},
+  { 55, 65, -1, sizeof(::PROTOBUF_NAMESPACE_ID::DescriptorProto_ReservedRange)},
+  { 67, 85, -1, sizeof(::PROTOBUF_NAMESPACE_ID::DescriptorProto)},
+  { 95, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::ExtensionRangeOptions)},
+  { 104, 123, -1, sizeof(::PROTOBUF_NAMESPACE_ID::FieldDescriptorProto)},
+  { 134, 144, -1, sizeof(::PROTOBUF_NAMESPACE_ID::OneofDescriptorProto)},
+  { 146, 156, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumDescriptorProto_EnumReservedRange)},
+  { 158, 171, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumDescriptorProto)},
+  { 176, 187, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumValueDescriptorProto)},
+  { 190, 201, -1, sizeof(::PROTOBUF_NAMESPACE_ID::ServiceDescriptorProto)},
+  { 204, 218, -1, sizeof(::PROTOBUF_NAMESPACE_ID::MethodDescriptorProto)},
+  { 224, 253, -1, sizeof(::PROTOBUF_NAMESPACE_ID::FileOptions)},
+  { 274, 287, -1, sizeof(::PROTOBUF_NAMESPACE_ID::MessageOptions)},
+  { 292, 308, -1, sizeof(::PROTOBUF_NAMESPACE_ID::FieldOptions)},
+  { 316, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::OneofOptions)},
+  { 325, 336, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumOptions)},
+  { 339, 349, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumValueOptions)},
+  { 351, 361, -1, sizeof(::PROTOBUF_NAMESPACE_ID::ServiceOptions)},
+  { 363, 374, -1, sizeof(::PROTOBUF_NAMESPACE_ID::MethodOptions)},
+  { 377, 387, -1, sizeof(::PROTOBUF_NAMESPACE_ID::UninterpretedOption_NamePart)},
+  { 389, 404, -1, sizeof(::PROTOBUF_NAMESPACE_ID::UninterpretedOption)},
+  { 411, 424, -1, sizeof(::PROTOBUF_NAMESPACE_ID::SourceCodeInfo_Location)},
+  { 429, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::SourceCodeInfo)},
+  { 438, 450, -1, sizeof(::PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo_Annotation)},
+  { 454, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::GeneratedCodeInfo)},
 };
 
 static const ::_pb::Message* const file_default_instances[] = {
diff --git a/src/google/protobuf/descriptor.pb.h b/src/google/protobuf/descriptor.pb.h
index 0a51ba353..78df1d512 100644
--- a/src/google/protobuf/descriptor.pb.h
+++ b/src/google/protobuf/descriptor.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/duration.pb.cc b/src/google/protobuf/duration.pb.cc
index 72766bd3b..94671ee6c 100644
--- a/src/google/protobuf/duration.pb.cc
+++ b/src/google/protobuf/duration.pb.cc
@@ -47,6 +47,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fduration_2eproto::offsets[] PROTO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Duration, _impl_.seconds_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Duration, _impl_.nanos_),
 };
diff --git a/src/google/protobuf/duration.pb.h b/src/google/protobuf/duration.pb.h
index 7bdff41c5..73193eb11 100644
--- a/src/google/protobuf/duration.pb.h
+++ b/src/google/protobuf/duration.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/dynamic_message.cc b/src/google/protobuf/dynamic_message.cc
index 1c96ca208..394056458 100644
--- a/src/google/protobuf/dynamic_message.cc
+++ b/src/google/protobuf/dynamic_message.cc
@@ -808,8 +808,11 @@ const Message* DynamicMessageFactory::GetPrototypeNoLock(
       type_info->oneof_case_offset,
       type_info->size,
       type_info->weak_field_map_offset,
-      nullptr /* inlined_string_indices_ */,
-      0 /* inlined_string_donated_offset_ */};
+      nullptr,  // inlined_string_indices_
+      0,        // inlined_string_donated_offset_
+      -1,       // split_offset_
+      -1,       // sizeof_split_
+  };
 
   type_info->reflection.reset(
       new Reflection(type_info->type, schema, type_info->pool, this));
diff --git a/src/google/protobuf/dynamic_message.h b/src/google/protobuf/dynamic_message.h
index 6fa64259e..e318259e0 100644
--- a/src/google/protobuf/dynamic_message.h
+++ b/src/google/protobuf/dynamic_message.h
@@ -81,6 +81,9 @@ class DescriptorPool;  // descriptor.h
 // encapsulates this "cache".  All DynamicMessages of the same type created
 // from the same factory will share the same support data.  Any Descriptors
 // used with a particular factory must outlive the factory.
+//
+// The thread safety for this class is subtle, see comments around GetPrototype
+// for details
 class PROTOBUF_EXPORT DynamicMessageFactory : public MessageFactory {
  public:
   // Construct a DynamicMessageFactory that will search for extensions in
diff --git a/src/google/protobuf/empty.pb.cc b/src/google/protobuf/empty.pb.cc
index 3a3077638..8af459dbf 100644
--- a/src/google/protobuf/empty.pb.cc
+++ b/src/google/protobuf/empty.pb.cc
@@ -44,6 +44,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fempty_2eproto::offsets[] PROTOBUF
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
 };
 static const ::_pbi::MigrationSchema schemas[] PROTOBUF_SECTION_VARIABLE(protodesc_cold) = {
   { 0, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Empty)},
diff --git a/src/google/protobuf/empty.pb.h b/src/google/protobuf/empty.pb.h
index 70fd45e60..f5c44b831 100644
--- a/src/google/protobuf/empty.pb.h
+++ b/src/google/protobuf/empty.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/field_mask.pb.cc b/src/google/protobuf/field_mask.pb.cc
index 7860bfbfe..8448013e6 100644
--- a/src/google/protobuf/field_mask.pb.cc
+++ b/src/google/protobuf/field_mask.pb.cc
@@ -46,6 +46,8 @@ const uint32_t TableStruct_google_2fprotobuf_2ffield_5fmask_2eproto::offsets[] P
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FieldMask, _impl_.paths_),
 };
 static const ::_pbi::MigrationSchema schemas[] PROTOBUF_SECTION_VARIABLE(protodesc_cold) = {
diff --git a/src/google/protobuf/field_mask.pb.h b/src/google/protobuf/field_mask.pb.h
index 9022e1f31..f4f77070d 100644
--- a/src/google/protobuf/field_mask.pb.h
+++ b/src/google/protobuf/field_mask.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/generated_message_reflection.cc b/src/google/protobuf/generated_message_reflection.cc
index 53ca9acd3..aefec9908 100644
--- a/src/google/protobuf/generated_message_reflection.cc
+++ b/src/google/protobuf/generated_message_reflection.cc
@@ -35,6 +35,7 @@
 #include <google/protobuf/generated_message_reflection.h>
 
 #include <algorithm>
+#include <cstring>
 #include <set>
 
 #include <google/protobuf/stubs/logging.h>
@@ -1114,8 +1115,14 @@ void Reflection::InternalSwap(Message* lhs, Message* rhs) const {
     const FieldDescriptor* field = descriptor_->field(i);
     if (schema_.InRealOneof(field)) continue;
     if (schema_.IsFieldStripped(field)) continue;
+    if (schema_.IsSplit(field)) {
+      continue;
+    }
     UnsafeShallowSwapField(lhs, rhs, field);
   }
+  if (schema_.IsSplit()) {
+    std::swap(*MutableSplitField(lhs), *MutableSplitField(rhs));
+  }
   const int oneof_decl_count = descriptor_->oneof_decl_count();
   for (int i = 0; i < oneof_decl_count; i++) {
     const OneofDescriptor* oneof = descriptor_->oneof_decl(i);
@@ -2437,13 +2444,34 @@ bool Reflection::SupportsUnknownEnumValues() const {
 template <class Type>
 const Type& Reflection::GetRawNonOneof(const Message& message,
                                        const FieldDescriptor* field) const {
+  if (schema_.IsSplit(field)) {
+    return *GetConstPointerAtOffset<Type>(
+        GetSplitField(&message), schema_.GetFieldOffsetNonOneof(field));
+  }
   return GetConstRefAtOffset<Type>(message,
                                    schema_.GetFieldOffsetNonOneof(field));
 }
 
+void Reflection::PrepareSplitMessageForWrite(Message* message) const {
+  void** split = MutableSplitField(message);
+  const void* default_split = GetSplitField(schema_.default_instance_);
+  if (*split == default_split) {
+    uint32_t size = schema_.SizeofSplit();
+    Arena* arena = message->GetArenaForAllocation();
+    *split = (arena == nullptr) ? ::operator new(size)
+                                : arena->AllocateAligned(size);
+    memcpy(*split, default_split, size);
+  }
+}
+
 template <class Type>
 Type* Reflection::MutableRawNonOneof(Message* message,
                                      const FieldDescriptor* field) const {
+  if (schema_.IsSplit(field)) {
+    PrepareSplitMessageForWrite(message);
+    return GetPointerAtOffset<Type>(*MutableSplitField(message),
+                                    schema_.GetFieldOffsetNonOneof(field));
+  }
   return GetPointerAtOffset<Type>(message,
                                   schema_.GetFieldOffsetNonOneof(field));
 }
@@ -2451,6 +2479,11 @@ Type* Reflection::MutableRawNonOneof(Message* message,
 template <typename Type>
 Type* Reflection::MutableRaw(Message* message,
                              const FieldDescriptor* field) const {
+  if (schema_.IsSplit(field)) {
+    PrepareSplitMessageForWrite(message);
+    return GetPointerAtOffset<Type>(*MutableSplitField(message),
+                                    schema_.GetFieldOffset(field));
+  }
   return GetPointerAtOffset<Type>(message, schema_.GetFieldOffset(field));
 }
 
@@ -2875,9 +2908,11 @@ ReflectionSchema MigrationToReflectionSchema(
     MigrationSchema migration_schema) {
   ReflectionSchema result;
   result.default_instance_ = *default_instance;
-  // First 7 offsets are offsets to the special fields. The following offsets
+  // First 9 offsets are offsets to the special fields. The following offsets
   // are the proto fields.
-  result.offsets_ = offsets + migration_schema.offsets_index + 6;
+  //
+  // TODO(congliu): Find a way to not encode sizeof_split_ in offsets.
+  result.offsets_ = offsets + migration_schema.offsets_index + 8;
   result.has_bit_indices_ = offsets + migration_schema.has_bit_indices_index;
   result.has_bits_offset_ = offsets[migration_schema.offsets_index + 0];
   result.metadata_offset_ = offsets[migration_schema.offsets_index + 1];
@@ -2887,6 +2922,8 @@ ReflectionSchema MigrationToReflectionSchema(
   result.weak_field_map_offset_ = offsets[migration_schema.offsets_index + 4];
   result.inlined_string_donated_offset_ =
       offsets[migration_schema.offsets_index + 5];
+  result.split_offset_ = offsets[migration_schema.offsets_index + 6];
+  result.sizeof_split_ = offsets[migration_schema.offsets_index + 7];
   result.inlined_string_indices_ =
       offsets + migration_schema.inlined_string_indices_index;
   return result;
diff --git a/src/google/protobuf/generated_message_reflection.h b/src/google/protobuf/generated_message_reflection.h
index 334b2ccf1..7d1b699d4 100644
--- a/src/google/protobuf/generated_message_reflection.h
+++ b/src/google/protobuf/generated_message_reflection.h
@@ -72,6 +72,19 @@ class DefaultEmptyOneof;
 class ExtensionSet;  // extension_set.h
 class WeakFieldMap;  // weak_field_map.h
 
+enum {
+  // Tag used on offsets for fields that don't have a real offset.
+  // For example, weak message fields go into the WeakFieldMap and not in an
+  // actual field.
+  kInvalidFieldOffsetTag = 0x40000000u,
+
+  // Mask used on offsets for split fields.
+  kSplitFieldOffsetMask = 0x80000000u,
+
+  kLazyMask = 0x1u,
+  kInlinedMask = 0x1u,
+};
+
 // This struct describes the internal layout of the message, hence this is
 // used to act on the message reflectively.
 //   default_instance:  The default instance of the message.  This is only
@@ -234,6 +247,24 @@ struct ReflectionSchema {
     return false;
   }
 
+  bool IsSplit() const { return split_offset_ != -1; }
+
+  bool IsSplit(const FieldDescriptor* field) const {
+    return split_offset_ != -1 &&
+           (offsets_[field->index()] & kSplitFieldOffsetMask) != 0;
+  }
+
+  // Byte offset of _split_.
+  uint32_t SplitOffset() const {
+    GOOGLE_DCHECK(IsSplit());
+    return static_cast<uint32_t>(split_offset_);
+  }
+
+  uint32_t SizeofSplit() const {
+    GOOGLE_DCHECK(IsSplit());
+    return static_cast<uint32_t>(sizeof_split_);
+  }
+
 
   bool HasWeakFields() const { return weak_field_map_offset_ > 0; }
 
@@ -254,6 +285,8 @@ struct ReflectionSchema {
   int weak_field_map_offset_;
   const uint32_t* inlined_string_indices_;
   int inlined_string_donated_offset_;
+  int split_offset_;
+  int sizeof_split_;
 
   // We tag offset values to provide additional data about fields (such as
   // "unused" or "lazy" or "inlined").
@@ -261,15 +294,15 @@ struct ReflectionSchema {
     if (type == FieldDescriptor::TYPE_MESSAGE ||
         type == FieldDescriptor::TYPE_STRING ||
         type == FieldDescriptor::TYPE_BYTES) {
-      return v & 0xFFFFFFFEu;
+      return v & (~kSplitFieldOffsetMask) & (~kInlinedMask) & (~kLazyMask);
     }
-    return v;
+    return v & (~kSplitFieldOffsetMask);
   }
 
   static bool Inlined(uint32_t v, FieldDescriptor::Type type) {
     if (type == FieldDescriptor::TYPE_STRING ||
         type == FieldDescriptor::TYPE_BYTES) {
-      return (v & 1u) != 0u;
+      return (v & kInlinedMask) != 0u;
     } else {
       // Non string/byte fields are not inlined.
       return false;
@@ -312,13 +345,6 @@ struct PROTOBUF_EXPORT DescriptorTable {
   const ServiceDescriptor** file_level_service_descriptors;
 };
 
-enum {
-  // Tag used on offsets for fields that don't have a real offset.
-  // For example, weak message fields go into the WeakFieldMap and not in an
-  // actual field.
-  kInvalidFieldOffsetTag = 0x40000000u,
-};
-
 // AssignDescriptors() pulls the compiled FileDescriptor from the DescriptorPool
 // and uses it to populate all of the global variables which store pointers to
 // the descriptor objects.  It also constructs the reflection objects.  It is
diff --git a/src/google/protobuf/generated_message_tctable_impl.h b/src/google/protobuf/generated_message_tctable_impl.h
index 53bdc76da..1ea1250f8 100644
--- a/src/google/protobuf/generated_message_tctable_impl.h
+++ b/src/google/protobuf/generated_message_tctable_impl.h
@@ -64,10 +64,11 @@ namespace internal {
 //     |15        ..          8|7         ..          0|
 //     +-----------------------+-----------------------+
 //     :  .  :  .  :  .  :  .  :  .  :  .  : 3|========| [3] FieldType
-//     :     :     :     :     :     : 5|=====|  :     : [2] FieldCardinality
-//     :  .  :  .  :  .  :  . 8|========|  :  .  :  .  : [3] FieldRep
-//     :     :     :   10|=====|     :     :     :     : [2] TransformValidation
-//     :  .  :  .12|=====|  .  :  .  :  .  :  .  :  .  : [2] FormatDiscriminator
+//     :     :     :     :     :     :  . 4|==|  :     : [1] FieldSplit
+//     :     :     :     :     :    6|=====|  .  :     : [2] FieldCardinality
+//     :  .  :  .  :  .  : 9|========|  .  :  .  :  .  : [3] FieldRep
+//     :     :     :11|=====|  :     :     :     :     : [2] TransformValidation
+//     :  .  :13|=====|  :  .  :  .  :  .  :  .  :  .  : [2] FormatDiscriminator
 //     +-----------------------+-----------------------+
 //     |15        ..          8|7         ..          0|
 //     +-----------------------+-----------------------+
@@ -95,11 +96,21 @@ enum FieldKind : uint16_t {
 
 static_assert(kFkMap < (1 << kFkBits), "too many types");
 
+// Split (1 bit):
+enum FieldSplit : uint16_t {
+  kSplitShift = kFkShift+ kFkBits,
+  kSplitBits  = 1,
+  kSplitMask  = ((1 << kSplitBits) - 1) << kSplitShift,
+
+  kSplitFalse = 0,
+  kSplitTrue  = 1 << kSplitShift,
+};
+
 // Cardinality (2 bits):
 // These values determine how many values a field can have and its presence.
 // Packed fields are represented in FieldType.
 enum Cardinality : uint16_t {
-  kFcShift    = kFkShift + kFkBits,
+  kFcShift    = kSplitShift+ kSplitBits,
   kFcBits     = 2,
   kFcMask     = ((1 << kFcBits) - 1) << kFcShift,
 
@@ -179,7 +190,7 @@ enum FormatDiscriminator : uint16_t {
 };
 
 // Update this assertion (and comments above) when adding or removing bits:
-static_assert(kFmtShift + kFmtBits == 12, "number of bits changed");
+static_assert(kFmtShift + kFmtBits == 13, "number of bits changed");
 
 // This assertion should not change unless the storage width changes:
 static_assert(kFmtShift + kFmtBits <= 16, "too many bits");
@@ -549,14 +560,18 @@ class PROTOBUF_EXPORT TcParser final {
   static constexpr const uint32_t kMtSmallScanSize = 4;
 
   // Mini parsing:
+  template <bool is_split>
   static const char* MpVarint(PROTOBUF_TC_PARAM_DECL);
   static const char* MpRepeatedVarint(PROTOBUF_TC_PARAM_DECL);
   static const char* MpPackedVarint(PROTOBUF_TC_PARAM_DECL);
+  template <bool is_split>
   static const char* MpFixed(PROTOBUF_TC_PARAM_DECL);
   static const char* MpRepeatedFixed(PROTOBUF_TC_PARAM_DECL);
   static const char* MpPackedFixed(PROTOBUF_TC_PARAM_DECL);
+  template <bool is_split>
   static const char* MpString(PROTOBUF_TC_PARAM_DECL);
   static const char* MpRepeatedString(PROTOBUF_TC_PARAM_DECL);
+  template <bool is_split>
   static const char* MpMessage(PROTOBUF_TC_PARAM_DECL);
   static const char* MpRepeatedMessage(PROTOBUF_TC_PARAM_DECL);
   static const char* MpMap(PROTOBUF_TC_PARAM_DECL);
diff --git a/src/google/protobuf/generated_message_tctable_lite.cc b/src/google/protobuf/generated_message_tctable_lite.cc
index 519b10776..1f13e83cc 100644
--- a/src/google/protobuf/generated_message_tctable_lite.cc
+++ b/src/google/protobuf/generated_message_tctable_lite.cc
@@ -315,24 +315,43 @@ const char* TcParser::MiniParse(PROTOBUF_TC_PARAM_DECL) {
   data.data = entry_offset << 32 | tag;
 
   using field_layout::FieldKind;
-  auto field_type = entry->type_card & FieldKind::kFkMask;
+  auto field_type =
+      entry->type_card & (+field_layout::kSplitMask | FieldKind::kFkMask);
   switch (field_type) {
     case FieldKind::kFkNone:
       PROTOBUF_MUSTTAIL return table->fallback(PROTOBUF_TC_PARAM_PASS);
     case FieldKind::kFkVarint:
-      PROTOBUF_MUSTTAIL return MpVarint(PROTOBUF_TC_PARAM_PASS);
+      PROTOBUF_MUSTTAIL return MpVarint<false>(PROTOBUF_TC_PARAM_PASS);
     case FieldKind::kFkPackedVarint:
       PROTOBUF_MUSTTAIL return MpPackedVarint(PROTOBUF_TC_PARAM_PASS);
     case FieldKind::kFkFixed:
-      PROTOBUF_MUSTTAIL return MpFixed(PROTOBUF_TC_PARAM_PASS);
+      PROTOBUF_MUSTTAIL return MpFixed<false>(PROTOBUF_TC_PARAM_PASS);
     case FieldKind::kFkPackedFixed:
       PROTOBUF_MUSTTAIL return MpPackedFixed(PROTOBUF_TC_PARAM_PASS);
     case FieldKind::kFkString:
-      PROTOBUF_MUSTTAIL return MpString(PROTOBUF_TC_PARAM_PASS);
+      PROTOBUF_MUSTTAIL return MpString<false>(PROTOBUF_TC_PARAM_PASS);
     case FieldKind::kFkMessage:
-      PROTOBUF_MUSTTAIL return MpMessage(PROTOBUF_TC_PARAM_PASS);
+      PROTOBUF_MUSTTAIL return MpMessage<false>(PROTOBUF_TC_PARAM_PASS);
     case FieldKind::kFkMap:
       PROTOBUF_MUSTTAIL return MpMap(PROTOBUF_TC_PARAM_PASS);
+
+    case +field_layout::kSplitMask | FieldKind::kFkNone:
+      PROTOBUF_FALLTHROUGH_INTENDED;
+    case +field_layout::kSplitMask | FieldKind::kFkPackedVarint:
+      PROTOBUF_FALLTHROUGH_INTENDED;
+    case +field_layout::kSplitMask | FieldKind::kFkPackedFixed:
+      PROTOBUF_FALLTHROUGH_INTENDED;
+    case +field_layout::kSplitMask | FieldKind::kFkMap:
+      return Error(PROTOBUF_TC_PARAM_PASS);
+
+    case +field_layout::kSplitMask | FieldKind::kFkVarint:
+      PROTOBUF_MUSTTAIL return MpVarint<true>(PROTOBUF_TC_PARAM_PASS);
+    case +field_layout::kSplitMask | FieldKind::kFkFixed:
+      PROTOBUF_MUSTTAIL return MpFixed<true>(PROTOBUF_TC_PARAM_PASS);
+    case +field_layout::kSplitMask | FieldKind::kFkString:
+      PROTOBUF_MUSTTAIL return MpString<true>(PROTOBUF_TC_PARAM_PASS);
+    case +field_layout::kSplitMask | FieldKind::kFkMessage:
+      PROTOBUF_MUSTTAIL return MpMessage<true>(PROTOBUF_TC_PARAM_PASS);
     default:
       return Error(PROTOBUF_TC_PARAM_PASS);
   }
@@ -1392,6 +1411,43 @@ bool TcParser::ChangeOneof(const TcParseTableBase* table,
   return true;
 }
 
+namespace {
+enum {
+  kSplitOffsetIdx = 2,
+  kSplitSizeIdx = 3,
+};
+uint32_t GetSplitOffset(const TcParseTableBase* table) {
+  return table->field_aux(kSplitOffsetIdx)->offset;
+}
+
+uint32_t GetSizeofSplit(const TcParseTableBase* table) {
+  return table->field_aux(kSplitSizeIdx)->offset;
+}
+
+void* MaybeGetSplitBase(MessageLite* msg, const bool is_split,
+                        const TcParseTableBase* table,
+                        ::google::protobuf::internal::ParseContext* ctx) {
+  void* out = msg;
+  if (is_split) {
+    const uint32_t split_offset = GetSplitOffset(table);
+    void* default_split =
+        TcParser::RefAt<void*>(table->default_instance, split_offset);
+    void*& split = TcParser::RefAt<void*>(msg, split_offset);
+    if (split == default_split) {
+      // Allocate split instance when needed.
+      uint32_t size = GetSizeofSplit(table);
+      Arena* arena = ctx->data().arena;
+      split = (arena == nullptr) ? ::operator new(size)
+                                 : arena->AllocateAligned(size);
+      memcpy(split, default_split, size);
+    }
+    out = split;
+  }
+  return out;
+}
+}  // namespace
+
+template <bool is_split>
 const char* TcParser::MpFixed(PROTOBUF_TC_PARAM_DECL) {
   const auto& entry = RefAt<FieldEntry>(table, data.entry_offset());
   const uint16_t type_card = entry.type_card;
@@ -1420,12 +1476,13 @@ const char* TcParser::MpFixed(PROTOBUF_TC_PARAM_DECL) {
   } else if (card == field_layout::kFcOneof) {
     ChangeOneof(table, entry, data.tag() >> 3, ctx, msg);
   }
+  void* const base = MaybeGetSplitBase(msg, is_split, table, ctx);
   // Copy the value:
   if (rep == field_layout::kRep64Bits) {
-    RefAt<uint64_t>(msg, entry.offset) = UnalignedLoad<uint64_t>(ptr);
+    RefAt<uint64_t>(base, entry.offset) = UnalignedLoad<uint64_t>(ptr);
     ptr += sizeof(uint64_t);
   } else {
-    RefAt<uint32_t>(msg, entry.offset) = UnalignedLoad<uint32_t>(ptr);
+    RefAt<uint32_t>(base, entry.offset) = UnalignedLoad<uint32_t>(ptr);
     ptr += sizeof(uint32_t);
   }
   PROTOBUF_MUSTTAIL return ToTagDispatch(PROTOBUF_TC_PARAM_PASS);
@@ -1510,6 +1567,7 @@ const char* TcParser::MpPackedFixed(PROTOBUF_TC_PARAM_DECL) {
   PROTOBUF_MUSTTAIL return ToTagDispatch(PROTOBUF_TC_PARAM_PASS);
 }
 
+template <bool is_split>
 const char* TcParser::MpVarint(PROTOBUF_TC_PARAM_DECL) {
   const auto& entry = RefAt<FieldEntry>(table, data.entry_offset());
   const uint16_t type_card = entry.type_card;
@@ -1558,13 +1616,14 @@ const char* TcParser::MpVarint(PROTOBUF_TC_PARAM_DECL) {
     ChangeOneof(table, entry, data.tag() >> 3, ctx, msg);
   }
 
+  void* const base = MaybeGetSplitBase(msg, is_split, table, ctx);
   if (rep == field_layout::kRep64Bits) {
-    RefAt<uint64_t>(msg, entry.offset) = tmp;
+    RefAt<uint64_t>(base, entry.offset) = tmp;
   } else if (rep == field_layout::kRep32Bits) {
-    RefAt<uint32_t>(msg, entry.offset) = static_cast<uint32_t>(tmp);
+    RefAt<uint32_t>(base, entry.offset) = static_cast<uint32_t>(tmp);
   } else {
     GOOGLE_DCHECK_EQ(rep, static_cast<uint16_t>(field_layout::kRep8Bits));
-    RefAt<bool>(msg, entry.offset) = static_cast<bool>(tmp);
+    RefAt<bool>(base, entry.offset) = static_cast<bool>(tmp);
   }
 
   PROTOBUF_MUSTTAIL return ToTagDispatch(PROTOBUF_TC_PARAM_PASS);
@@ -1705,6 +1764,7 @@ bool TcParser::MpVerifyUtf8(StringPiece wire_bytes,
   return true;
 }
 
+template <bool is_split>
 const char* TcParser::MpString(PROTOBUF_TC_PARAM_DECL) {
   const auto& entry = RefAt<FieldEntry>(table, data.entry_offset());
   const uint16_t type_card = entry.type_card;
@@ -1735,9 +1795,10 @@ const char* TcParser::MpString(PROTOBUF_TC_PARAM_DECL) {
 
   bool is_valid = false;
   Arena* arena = ctx->data().arena;
+  void* const base = MaybeGetSplitBase(msg, is_split, table, ctx);
   switch (rep) {
     case field_layout::kRepAString: {
-      auto& field = RefAt<ArenaStringPtr>(msg, entry.offset);
+      auto& field = RefAt<ArenaStringPtr>(base, entry.offset);
       if (need_init) field.InitDefault();
       if (arena) {
         ptr = ctx->ReadArenaString(ptr, &field, arena);
@@ -1803,6 +1864,7 @@ const char* TcParser::MpRepeatedString(PROTOBUF_TC_PARAM_DECL) {
   return ToParseLoop(PROTOBUF_TC_PARAM_PASS);
 }
 
+template <bool is_split>
 const char* TcParser::MpMessage(PROTOBUF_TC_PARAM_DECL) {
   const auto& entry = RefAt<FieldEntry>(table, data.entry_offset());
   const uint16_t type_card = entry.type_card;
@@ -1845,8 +1907,10 @@ const char* TcParser::MpMessage(PROTOBUF_TC_PARAM_DECL) {
   } else if (is_oneof) {
     need_init = ChangeOneof(table, entry, data.tag() >> 3, ctx, msg);
   }
+
+  void* const base = MaybeGetSplitBase(msg, is_split, table, ctx);
   SyncHasbits(msg, hasbits, table);
-  MessageLite*& field = RefAt<MessageLite*>(msg, entry.offset);
+  MessageLite*& field = RefAt<MessageLite*>(base, entry.offset);
   if ((type_card & field_layout::kTvMask) == field_layout::kTvTable) {
     auto* inner_table = table->field_aux(&entry)->table;
     if (need_init || field == nullptr) {
diff --git a/src/google/protobuf/inlined_string_field.h b/src/google/protobuf/inlined_string_field.h
index 79e37d414..71bd6a7eb 100644
--- a/src/google/protobuf/inlined_string_field.h
+++ b/src/google/protobuf/inlined_string_field.h
@@ -427,7 +427,7 @@ inline PROTOBUF_NDEBUG_INLINE void InlinedStringField::InternalSwap(
     MessageLite* lhs_msg,  //
     InlinedStringField* rhs, Arena* rhs_arena, bool rhs_arena_dtor_registered,
     MessageLite* rhs_msg) {
-#if GOOGLE_PROTOBUF_INTERNAL_DONATE_STEAL_INLINE
+#ifdef GOOGLE_PROTOBUF_INTERNAL_DONATE_STEAL_INLINE
   lhs->get_mutable()->swap(*rhs->get_mutable());
   if (!lhs_arena_dtor_registered && rhs_arena_dtor_registered) {
     lhs_msg->OnDemandRegisterArenaDtor(lhs_arena);
diff --git a/src/google/protobuf/io/BUILD.bazel b/src/google/protobuf/io/BUILD.bazel
index 7582f78bc..bf0d87cbd 100644
--- a/src/google/protobuf/io/BUILD.bazel
+++ b/src/google/protobuf/io/BUILD.bazel
@@ -114,6 +114,7 @@ cc_test(
         ":gzip_stream",
         ":io",
         "//:protobuf",
+        "//src/google/protobuf:test_util2",
         "//src/google/protobuf/testing",
         "@com_google_googletest//:gtest",
         "@com_google_googletest//:gtest_main",
@@ -144,3 +145,12 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]),
+    visibility = ["//pkg:__pkg__"],
+)
diff --git a/src/google/protobuf/message.cc b/src/google/protobuf/message.cc
index 6cdc6c839..3e044f742 100644
--- a/src/google/protobuf/message.cc
+++ b/src/google/protobuf/message.cc
@@ -213,6 +213,16 @@ uint64_t Message::GetInvariantPerBuild(uint64_t salt) {
   return salt;
 }
 
+namespace internal {
+void* CreateSplitMessageGeneric(Arena* arena, void* default_split,
+                                size_t size) {
+  void* split =
+      (arena == nullptr) ? ::operator new(size) : arena->AllocateAligned(size);
+  memcpy(split, default_split, size);
+  return split;
+}
+}  // namespace internal
+
 // =============================================================================
 // MessageFactory
 
diff --git a/src/google/protobuf/message.h b/src/google/protobuf/message.h
index d20963bc6..82873885b 100644
--- a/src/google/protobuf/message.h
+++ b/src/google/protobuf/message.h
@@ -203,12 +203,12 @@ struct Metadata {
 
 namespace internal {
 template <class To>
-inline To* GetPointerAtOffset(Message* message, uint32_t offset) {
+inline To* GetPointerAtOffset(void* message, uint32_t offset) {
   return reinterpret_cast<To*>(reinterpret_cast<char*>(message) + offset);
 }
 
 template <class To>
-const To* GetConstPointerAtOffset(const Message* message, uint32_t offset) {
+const To* GetConstPointerAtOffset(const void* message, uint32_t offset) {
   return reinterpret_cast<const To*>(reinterpret_cast<const char*>(message) +
                                      offset);
 }
@@ -406,6 +406,9 @@ class PROTOBUF_EXPORT Message : public MessageLite {
 };
 
 namespace internal {
+// Creates and returns an allocation for a split message.
+void* CreateSplitMessageGeneric(Arena* arena, void* default_split, size_t size);
+
 // Forward-declare interfaces used to implement RepeatedFieldRef.
 // These are protobuf internals that users shouldn't care about.
 class RepeatedFieldAccessor;
@@ -1029,6 +1032,10 @@ class PROTOBUF_EXPORT Reflection final {
   bool IsLazilyVerifiedLazyField(const FieldDescriptor* field) const;
   bool IsEagerlyVerifiedLazyField(const FieldDescriptor* field) const;
 
+  bool IsSplit(const FieldDescriptor* field) const {
+    return schema_.IsSplit(field);
+  }
+
   friend class FastReflectionMessageMutator;
   friend bool internal::IsDescendant(Message& root, const Message& message);
 
@@ -1174,6 +1181,14 @@ class PROTOBUF_EXPORT Reflection final {
   inline void SwapInlinedStringDonated(Message* lhs, Message* rhs,
                                        const FieldDescriptor* field) const;
 
+  // Returns the `_split_` pointer. Requires: IsSplit() == true.
+  inline const void* GetSplitField(const Message* message) const;
+  // Returns the address of the `_split_` pointer. Requires: IsSplit() == true.
+  inline void** MutableSplitField(Message* message) const;
+
+  // Allocate the split instance if needed.
+  void PrepareSplitMessageForWrite(Message* message) const;
+
   // Shallow-swap fields listed in fields vector of two messages. It is the
   // caller's responsibility to make sure shallow swap is safe.
   void UnsafeShallowSwapFields(
@@ -1267,6 +1282,9 @@ class PROTOBUF_EXPORT Reflection final {
 };
 
 // Abstract interface for a factory for message objects.
+//
+// The thread safety for this class is implementation dependent, see comments
+// around GetPrototype for details
 class PROTOBUF_EXPORT MessageFactory {
  public:
   inline MessageFactory() {}
@@ -1483,11 +1501,26 @@ bool Reflection::HasOneofField(const Message& message,
           static_cast<uint32_t>(field->number()));
 }
 
+const void* Reflection::GetSplitField(const Message* message) const {
+  GOOGLE_DCHECK(schema_.IsSplit());
+  return *internal::GetConstPointerAtOffset<void*>(message,
+                                                   schema_.SplitOffset());
+}
+
+void** Reflection::MutableSplitField(Message* message) const {
+  GOOGLE_DCHECK(schema_.IsSplit());
+  return internal::GetPointerAtOffset<void*>(message, schema_.SplitOffset());
+}
+
 template <typename Type>
 const Type& Reflection::GetRaw(const Message& message,
                                const FieldDescriptor* field) const {
   GOOGLE_DCHECK(!schema_.InRealOneof(field) || HasOneofField(message, field))
       << "Field = " << field->full_name();
+  if (schema_.IsSplit(field)) {
+    return *internal::GetConstPointerAtOffset<Type>(
+        GetSplitField(&message), schema_.GetFieldOffset(field));
+  }
   return internal::GetConstRefAtOffset<Type>(message,
                                              schema_.GetFieldOffset(field));
 }
diff --git a/src/google/protobuf/port_def.inc b/src/google/protobuf/port_def.inc
index 38779a347..0b463b8c6 100644
--- a/src/google/protobuf/port_def.inc
+++ b/src/google/protobuf/port_def.inc
@@ -178,7 +178,7 @@
 #ifdef PROTOBUF_VERSION
 #error PROTOBUF_VERSION was previously defined
 #endif
-#define PROTOBUF_VERSION 3021000
+#define PROTOBUF_VERSION 3021001
 
 #ifdef PROTOBUF_MIN_HEADER_VERSION_FOR_PROTOC
 #error PROTOBUF_MIN_HEADER_VERSION_FOR_PROTOC was previously defined
@@ -193,7 +193,7 @@
 #ifdef PROTOBUF_VERSION_SUFFIX
 #error PROTOBUF_VERSION_SUFFIX was previously defined
 #endif
-#define PROTOBUF_VERSION_SUFFIX "-rc2"
+#define PROTOBUF_VERSION_SUFFIX ""
 
 #if defined(PROTOBUF_NAMESPACE) || defined(PROTOBUF_NAMESPACE_ID)
 #error PROTOBUF_NAMESPACE or PROTOBUF_NAMESPACE_ID was previously defined
@@ -798,7 +798,7 @@
 
 // Windows declares several inconvenient macro names.  We #undef them and then
 // restore them in port_undef.inc.
-#ifdef _MSC_VER
+#ifdef _WIN32
 #pragma push_macro("CREATE_NEW")
 #undef CREATE_NEW
 #pragma push_macro("DELETE")
@@ -851,7 +851,7 @@
 #undef STRICT
 #pragma push_macro("timezone")
 #undef timezone
-#endif  // _MSC_VER
+#endif  // _WIN32
 
 #ifdef __APPLE__
 // Inconvenient macro names from usr/include/math.h in some macOS SDKs.
diff --git a/src/google/protobuf/port_undef.inc b/src/google/protobuf/port_undef.inc
index f8968d9a8..44663219f 100644
--- a/src/google/protobuf/port_undef.inc
+++ b/src/google/protobuf/port_undef.inc
@@ -110,7 +110,7 @@
 #endif
 
 // Restore macro that may have been #undef'd in port_def.inc.
-#ifdef _MSC_VER
+#ifdef _WIN32
 #pragma pop_macro("CREATE_NEW")
 #pragma pop_macro("DELETE")
 #pragma pop_macro("DOUBLE_CLICK")
diff --git a/src/google/protobuf/repeated_field.h b/src/google/protobuf/repeated_field.h
index a74832f78..06b3353cc 100644
--- a/src/google/protobuf/repeated_field.h
+++ b/src/google/protobuf/repeated_field.h
@@ -94,23 +94,6 @@ constexpr int RepeatedFieldLowerClampLimit() {
 constexpr int kRepeatedFieldUpperClampLimit =
     (std::numeric_limits<int>::max() / 2) + 1;
 
-template <typename Iter>
-inline int CalculateReserve(Iter begin, Iter end, std::forward_iterator_tag) {
-  return static_cast<int>(std::distance(begin, end));
-}
-
-template <typename Iter>
-inline int CalculateReserve(Iter /*begin*/, Iter /*end*/,
-                            std::input_iterator_tag /*unused*/) {
-  return -1;
-}
-
-template <typename Iter>
-inline int CalculateReserve(Iter begin, Iter end) {
-  typedef typename std::iterator_traits<Iter>::iterator_category Category;
-  return CalculateReserve(begin, end, Category());
-}
-
 // Swaps two blocks of memory of size sizeof(T).
 template <typename T>
 inline void SwapBlock(char* p, char* q) {
@@ -722,13 +705,13 @@ inline Element* RepeatedField<Element>::Add() {
 template <typename Element>
 template <typename Iter>
 inline void RepeatedField<Element>::Add(Iter begin, Iter end) {
-  int reserve = internal::CalculateReserve(begin, end);
-  if (reserve != -1) {
-    if (reserve == 0) {
-      return;
-    }
+  if (std::is_base_of<
+          std::forward_iterator_tag,
+          typename std::iterator_traits<Iter>::iterator_category>::value) {
+    int additional = std::distance(begin, end);
+    if (additional == 0) return;
 
-    Reserve(reserve + size());
+    Reserve(size() + additional);
     // TODO(ckennelly):  The compiler loses track of the buffer freshly
     // allocated by Reserve() by the time we call elements, so it cannot
     // guarantee that elements does not alias [begin(), end()).
@@ -736,7 +719,7 @@ inline void RepeatedField<Element>::Add(Iter begin, Iter end) {
     // If restrict is available, annotating the pointer obtained from elements()
     // causes this to lower to memcpy instead of memmove.
     std::copy(begin, end, elements() + size());
-    current_size_ = reserve + size();
+    current_size_ = size() + additional;
   } else {
     FastAdder fast_adder(this);
     for (; begin != end; ++begin) fast_adder.Add(*begin);
diff --git a/src/google/protobuf/source_context.pb.cc b/src/google/protobuf/source_context.pb.cc
index e7525e99c..89118797b 100644
--- a/src/google/protobuf/source_context.pb.cc
+++ b/src/google/protobuf/source_context.pb.cc
@@ -46,6 +46,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fsource_5fcontext_2eproto::offsets
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::SourceContext, _impl_.file_name_),
 };
 static const ::_pbi::MigrationSchema schemas[] PROTOBUF_SECTION_VARIABLE(protodesc_cold) = {
diff --git a/src/google/protobuf/source_context.pb.h b/src/google/protobuf/source_context.pb.h
index 3625ece1f..63204f789 100644
--- a/src/google/protobuf/source_context.pb.h
+++ b/src/google/protobuf/source_context.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/struct.pb.cc b/src/google/protobuf/struct.pb.cc
index 87c72d4aa..43c1eae0a 100644
--- a/src/google/protobuf/struct.pb.cc
+++ b/src/google/protobuf/struct.pb.cc
@@ -84,6 +84,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fstruct_2eproto::offsets[] PROTOBU
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Struct_FieldsEntry_DoNotUse, key_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Struct_FieldsEntry_DoNotUse, value_),
   0,
@@ -94,6 +96,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fstruct_2eproto::offsets[] PROTOBU
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Struct, _impl_.fields_),
   ~0u,  // no _has_bits_
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Value, _internal_metadata_),
@@ -101,6 +105,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fstruct_2eproto::offsets[] PROTOBU
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Value, _impl_._oneof_case_[0]),
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   ::_pbi::kInvalidFieldOffsetTag,
   ::_pbi::kInvalidFieldOffsetTag,
   ::_pbi::kInvalidFieldOffsetTag,
@@ -114,13 +120,15 @@ const uint32_t TableStruct_google_2fprotobuf_2fstruct_2eproto::offsets[] PROTOBU
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::ListValue, _impl_.values_),
 };
 static const ::_pbi::MigrationSchema schemas[] PROTOBUF_SECTION_VARIABLE(protodesc_cold) = {
-  { 0, 8, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Struct_FieldsEntry_DoNotUse)},
-  { 10, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Struct)},
-  { 17, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Value)},
-  { 30, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::ListValue)},
+  { 0, 10, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Struct_FieldsEntry_DoNotUse)},
+  { 12, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Struct)},
+  { 21, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Value)},
+  { 36, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::ListValue)},
 };
 
 static const ::_pb::Message* const file_default_instances[] = {
diff --git a/src/google/protobuf/struct.pb.h b/src/google/protobuf/struct.pb.h
index a8019f86b..137227176 100644
--- a/src/google/protobuf/struct.pb.h
+++ b/src/google/protobuf/struct.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/stubs/BUILD.bazel b/src/google/protobuf/stubs/BUILD.bazel
index 2446352ec..73def31f5 100644
--- a/src/google/protobuf/stubs/BUILD.bazel
+++ b/src/google/protobuf/stubs/BUILD.bazel
@@ -136,3 +136,12 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]),
+    visibility = ["//pkg:__pkg__"],
+)
diff --git a/src/google/protobuf/stubs/common.h b/src/google/protobuf/stubs/common.h
index 36a4b08e4..81fb42718 100644
--- a/src/google/protobuf/stubs/common.h
+++ b/src/google/protobuf/stubs/common.h
@@ -82,10 +82,10 @@ namespace internal {
 
 // The current version, represented as a single integer to make comparison
 // easier:  major * 10^6 + minor * 10^3 + micro
-#define GOOGLE_PROTOBUF_VERSION 3021000
+#define GOOGLE_PROTOBUF_VERSION 3021001
 
 // A suffix string for alpha, beta or rc releases. Empty for stable releases.
-#define GOOGLE_PROTOBUF_VERSION_SUFFIX "-rc2"
+#define GOOGLE_PROTOBUF_VERSION_SUFFIX ""
 
 // The minimum header version which works with the current version of
 // the library.  This constant should only be used by protoc's C++ code
diff --git a/src/google/protobuf/timestamp.pb.cc b/src/google/protobuf/timestamp.pb.cc
index 728a00438..09b1b176d 100644
--- a/src/google/protobuf/timestamp.pb.cc
+++ b/src/google/protobuf/timestamp.pb.cc
@@ -47,6 +47,8 @@ const uint32_t TableStruct_google_2fprotobuf_2ftimestamp_2eproto::offsets[] PROT
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Timestamp, _impl_.seconds_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Timestamp, _impl_.nanos_),
 };
diff --git a/src/google/protobuf/timestamp.pb.h b/src/google/protobuf/timestamp.pb.h
index 01c8c8500..7c074c4f0 100644
--- a/src/google/protobuf/timestamp.pb.h
+++ b/src/google/protobuf/timestamp.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/type.pb.cc b/src/google/protobuf/type.pb.cc
index e29bbb83a..4f76508f7 100644
--- a/src/google/protobuf/type.pb.cc
+++ b/src/google/protobuf/type.pb.cc
@@ -119,6 +119,8 @@ const uint32_t TableStruct_google_2fprotobuf_2ftype_2eproto::offsets[] PROTOBUF_
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Type, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Type, _impl_.fields_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Type, _impl_.oneofs_),
@@ -131,6 +133,8 @@ const uint32_t TableStruct_google_2fprotobuf_2ftype_2eproto::offsets[] PROTOBUF_
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Field, _impl_.kind_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Field, _impl_.cardinality_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Field, _impl_.number_),
@@ -147,6 +151,8 @@ const uint32_t TableStruct_google_2fprotobuf_2ftype_2eproto::offsets[] PROTOBUF_
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Enum, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Enum, _impl_.enumvalue_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Enum, _impl_.options_),
@@ -158,6 +164,8 @@ const uint32_t TableStruct_google_2fprotobuf_2ftype_2eproto::offsets[] PROTOBUF_
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumValue, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumValue, _impl_.number_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::EnumValue, _impl_.options_),
@@ -167,15 +175,17 @@ const uint32_t TableStruct_google_2fprotobuf_2ftype_2eproto::offsets[] PROTOBUF_
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Option, _impl_.name_),
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Option, _impl_.value_),
 };
 static const ::_pbi::MigrationSchema schemas[] PROTOBUF_SECTION_VARIABLE(protodesc_cold) = {
   { 0, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Type)},
-  { 12, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Field)},
-  { 28, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Enum)},
-  { 39, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumValue)},
-  { 48, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Option)},
+  { 14, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Field)},
+  { 32, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Enum)},
+  { 45, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::EnumValue)},
+  { 56, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Option)},
 };
 
 static const ::_pb::Message* const file_default_instances[] = {
diff --git a/src/google/protobuf/type.pb.h b/src/google/protobuf/type.pb.h
index ecdb9d9ed..83439e999 100644
--- a/src/google/protobuf/type.pb.h
+++ b/src/google/protobuf/type.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/util/BUILD.bazel b/src/google/protobuf/util/BUILD.bazel
index 4fb8319d2..0443c52f6 100644
--- a/src/google/protobuf/util/BUILD.bazel
+++ b/src/google/protobuf/util/BUILD.bazel
@@ -27,6 +27,7 @@ cc_test(
     deps = [
         ":delimited_message_util",
         "//src/google/protobuf:cc_test_protos",
+        "//src/google/protobuf:test_util",
         "//src/google/protobuf/testing",
         "@com_google_googletest//:gtest",
         "@com_google_googletest//:gtest_main",
@@ -217,8 +218,13 @@ filegroup(
     srcs = [
         "json_format.proto",
         "json_format_proto3.proto",
+        "message_differencer_unittest.proto",
+        "//src/google/protobuf/util/internal:test_proto_srcs",
+    ],
+    visibility = [
+        "//pkg:__pkg__",
+        "//python:__pkg__",
     ],
-    visibility = ["//python:__pkg__"],
 )
 
 proto_library(
@@ -280,3 +286,14 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]) + [
+        "//src/google/protobuf/util/internal:test_srcs",
+    ],
+    visibility = ["//pkg:__pkg__"],
+)
diff --git a/src/google/protobuf/util/internal/BUILD.bazel b/src/google/protobuf/util/internal/BUILD.bazel
index d42ecad51..b1cdc6990 100644
--- a/src/google/protobuf/util/internal/BUILD.bazel
+++ b/src/google/protobuf/util/internal/BUILD.bazel
@@ -8,7 +8,10 @@ load("@rules_proto//proto:defs.bzl", "proto_library")
 load("//build_defs:cpp_opts.bzl", "COPTS")
 
 package(
-    default_visibility = ["//src/google/protobuf/util:__pkg__"],
+    default_visibility = [
+        "//src/google/protobuf/util:__pkg__",
+        "//pkg:__pkg__",
+    ],
 )
 
 cc_library(
@@ -448,3 +451,18 @@ pkg_files(
     strip_prefix = strip_prefix.from_root(""),
     visibility = ["//src:__pkg__"],
 )
+
+filegroup(
+    name = "test_srcs",
+    srcs = glob([
+        "*_test.cc",
+        "*unittest.cc",
+    ]) + [
+        "type_info_test_helper.cc",
+    ],
+)
+
+filegroup(
+    name = "test_proto_srcs",
+    srcs = glob(["testdata/*.proto"]),
+)
diff --git a/src/google/protobuf/wrappers.pb.cc b/src/google/protobuf/wrappers.pb.cc
index 40ba60a49..7f78690e6 100644
--- a/src/google/protobuf/wrappers.pb.cc
+++ b/src/google/protobuf/wrappers.pb.cc
@@ -150,6 +150,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fwrappers_2eproto::offsets[] PROTO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::DoubleValue, _impl_.value_),
   ~0u,  // no _has_bits_
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FloatValue, _internal_metadata_),
@@ -157,6 +159,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fwrappers_2eproto::offsets[] PROTO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::FloatValue, _impl_.value_),
   ~0u,  // no _has_bits_
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Int64Value, _internal_metadata_),
@@ -164,6 +168,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fwrappers_2eproto::offsets[] PROTO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Int64Value, _impl_.value_),
   ~0u,  // no _has_bits_
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::UInt64Value, _internal_metadata_),
@@ -171,6 +177,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fwrappers_2eproto::offsets[] PROTO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::UInt64Value, _impl_.value_),
   ~0u,  // no _has_bits_
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Int32Value, _internal_metadata_),
@@ -178,6 +186,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fwrappers_2eproto::offsets[] PROTO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::Int32Value, _impl_.value_),
   ~0u,  // no _has_bits_
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::UInt32Value, _internal_metadata_),
@@ -185,6 +195,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fwrappers_2eproto::offsets[] PROTO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::UInt32Value, _impl_.value_),
   ~0u,  // no _has_bits_
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::BoolValue, _internal_metadata_),
@@ -192,6 +204,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fwrappers_2eproto::offsets[] PROTO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::BoolValue, _impl_.value_),
   ~0u,  // no _has_bits_
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::StringValue, _internal_metadata_),
@@ -199,6 +213,8 @@ const uint32_t TableStruct_google_2fprotobuf_2fwrappers_2eproto::offsets[] PROTO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::StringValue, _impl_.value_),
   ~0u,  // no _has_bits_
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::BytesValue, _internal_metadata_),
@@ -206,18 +222,20 @@ const uint32_t TableStruct_google_2fprotobuf_2fwrappers_2eproto::offsets[] PROTO
   ~0u,  // no _oneof_case_
   ~0u,  // no _weak_field_map_
   ~0u,  // no _inlined_string_donated_
+  ~0u,  // no _split_
+  ~0u,  // no sizeof(Split)
   PROTOBUF_FIELD_OFFSET(::PROTOBUF_NAMESPACE_ID::BytesValue, _impl_.value_),
 };
 static const ::_pbi::MigrationSchema schemas[] PROTOBUF_SECTION_VARIABLE(protodesc_cold) = {
   { 0, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::DoubleValue)},
-  { 7, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::FloatValue)},
-  { 14, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Int64Value)},
-  { 21, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::UInt64Value)},
-  { 28, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Int32Value)},
-  { 35, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::UInt32Value)},
-  { 42, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::BoolValue)},
-  { 49, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::StringValue)},
-  { 56, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::BytesValue)},
+  { 9, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::FloatValue)},
+  { 18, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Int64Value)},
+  { 27, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::UInt64Value)},
+  { 36, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::Int32Value)},
+  { 45, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::UInt32Value)},
+  { 54, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::BoolValue)},
+  { 63, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::StringValue)},
+  { 72, -1, -1, sizeof(::PROTOBUF_NAMESPACE_ID::BytesValue)},
 };
 
 static const ::_pb::Message* const file_default_instances[] = {
diff --git a/src/google/protobuf/wrappers.pb.h b/src/google/protobuf/wrappers.pb.h
index 538dba60e..6f549dd97 100644
--- a/src/google/protobuf/wrappers.pb.h
+++ b/src/google/protobuf/wrappers.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3021000 < PROTOBUF_MIN_PROTOC_VERSION
+#if 3021001 < PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/third_party/benchmark b/third_party/benchmark
index 0baacde36..5b7683f49 160000
--- a/third_party/benchmark
+++ b/third_party/benchmark
@@ -1 +1 @@
-Subproject commit 0baacde3618ca617da95375e0af13ce1baadea47
+Subproject commit 5b7683f49e1e9223cf9927b24f6fd3d6bd82e3f8