diff --git a/CHANGELOG.md b/CHANGELOG.md
index 63bed9bde..5a12370dd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,21 @@
+# 2021-08-29 version 4.0.0 for C++
+  * Improve zone alignment logic (#965)
+  * Fix v1 unpack logic for STR and BIN (#957, #951)
+  * Fix UB on memcmp with size 0 (#954)
+  * Fix `iovec` name conflict (#952)
+  * Add `std::array<std::byte>` `std::span<char>` `std::span<unsigned char>` `std::span<std::byte>` adaptors (#951)
+  * Improve documents (#918, #919, #951)
+  * Improve tests (#916)
+  * Introduce BOOST_ASSERT (#898)
+  * Improve build system (#897, #905, #924, #951)
+  * Improve Boost.Fusion support (#894)
+  * Check nullptr before call memcpy (#891)
+  * Refine and bugfix `std::chrono::time_point` adaptor (#888, #893)
+  * Improve CI (#884, #892, #895, #951, #955)
+## << breaking changes >>
+  * Separate C++ part of the msgpack-c  from C/C++ mixed msgpack-c (#876, #878)
+  * Require boost libraries. See README.md Dependency(#912)
+
 # 2020-06-05 version 3.3.0
   * Add json example for C (#870)
   * Add both header and body packing functions for C (#870)
diff --git a/README.md b/README.md
index 6dbea6b14..c7a9e8143 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 `msgpack` for C++
 ===================
 
-Version 3.3.0 [![Build Status](https://github.com/msgpack/msgpack-c/workflows/CI/badge.svg?branch=cpp_master)](https://github.com/msgpack/msgpack-c/actions) [![Build status](https://ci.appveyor.com/api/projects/status/8kstcgt79qj123mw/branch/cpp_master?svg=true)](https://ci.appveyor.com/project/redboltz/msgpack-c/branch/cpp_master)
+Version 4.0.0 [![Build Status](https://github.com/msgpack/msgpack-c/workflows/CI/badge.svg?branch=cpp_master)](https://github.com/msgpack/msgpack-c/actions) [![Build status](https://ci.appveyor.com/api/projects/status/8kstcgt79qj123mw/branch/cpp_master?svg=true)](https://ci.appveyor.com/project/redboltz/msgpack-c/branch/cpp_master)
 [![codecov](https://codecov.io/gh/msgpack/msgpack-c/branch/cpp_master/graph/badge.svg)](https://codecov.io/gh/msgpack/msgpack-c/branch/cpp_master)
 
 It's like JSON but smaller and faster.
diff --git a/appveyor.yml b/appveyor.yml
index 25d005c1c..d19ae5a78 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -1,4 +1,4 @@
-version: 3.3.0.{build}
+version: 4.0.0.{build}
 
 branches:
   only:
diff --git a/include/msgpack/version_master.hpp b/include/msgpack/version_master.hpp
index 9db6023e7..763c732c7 100644
--- a/include/msgpack/version_master.hpp
+++ b/include/msgpack/version_master.hpp
@@ -1,3 +1,3 @@
-#define MSGPACK_VERSION_MAJOR    3
-#define MSGPACK_VERSION_MINOR    3
+#define MSGPACK_VERSION_MAJOR    4
+#define MSGPACK_VERSION_MINOR    0
 #define MSGPACK_VERSION_REVISION 0