diff --git a/README.md b/README.md
index b775ab0..9e2915d 100644
--- a/README.md
+++ b/README.md
@@ -17,8 +17,8 @@ C++17 and meson are required.
 Download the latest source package from the [GitHub Releases](https://github.com/serpapi/serpapi-cpp/releases) page, then run:
 
 ```bash
-tar xf serpapi-0.3.0.tar.xz
-cd serpapi-0.3.0
+tar xf serpapi-0.4.0.tar.xz
+cd serpapi-0.4.0
 meson setup build
 meson compile -C build
 sudo meson install -C build
@@ -194,6 +194,7 @@ C++ versions validated by Github Actions:
  - C++20
 
 ## Change logs
+ * [2026-06-08] 0.4.0 Add unit tests and improve error handling.
  * [2026-02-12] 0.3.0 Refactor and cleanup.
  * [2026-01-06] 0.2.0 Release package with meson build system.
  * [2023-02-20] 0.1.0 Full API support
diff --git a/meson.build b/meson.build
index 373b222..7e41c93 100644
--- a/meson.build
+++ b/meson.build
@@ -1,5 +1,5 @@
 project('serpapi', 'cpp',
-  version : '0.3.0',
+  version : '0.4.0',
   default_options : ['warning_level=3', 'cpp_std=c++17'])
 
 compiler = meson.get_compiler('cpp')
diff --git a/src/serpapi.cpp b/src/serpapi.cpp
index fd74b5a..7aee513 100644
--- a/src/serpapi.cpp
+++ b/src/serpapi.cpp
@@ -11,7 +11,7 @@ namespace serpapi {
 
 const static std::string HOST = "https://serpapi.com";
 const static std::string NAME = "serpapi-cpp";
-const static std::string VERSION = "0.3.0";
+const static std::string VERSION = "0.4.0";
 
 static std::once_flag curl_init_flag;