diff --git a/CMakeLists.txt b/CMakeLists.txt
index 02b4bfd..7aba108 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.20)
-project(claude_sdk VERSION 0.1.15 LANGUAGES CXX)
+project(claude_sdk VERSION 0.1.18 LANGUAGES CXX)
 
 # Enable folder organization in IDEs (Visual Studio, Xcode, etc.)
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
diff --git a/README.md b/README.md
index f19f818..e1bd64d 100644
--- a/README.md
+++ b/README.md
@@ -164,12 +164,14 @@ See `include/claude/types.hpp` and `docs/api-reference.md` for full details.
 
 ## Status & Parity
 
-- **Current version:** 0.1.15 (see `include/claude/version.hpp`).
+- **Current version:** 0.1.18 (see `include/claude/version.hpp`).
 - **Status:** Production ready.
-- **Parity:** Designed to match the Python Claude Agent SDK 0.1.15 API, behavior, and ergonomics, including MCP template APIs and control protocol.
+- **Parity:** Designed to match the Python Claude Agent SDK 0.1.18 API, behavior, and ergonomics, including MCP template APIs and control protocol.
 - **Tests:** See `kb/status.md` in the management repo for up-to-date test counts and parity details.
 
-**Canonical rule:** The Python `claude-agent-sdk` is the canonical reference. This C++ port is expected to track its behavior and API (currently aligned with Python v0.1.15).
+**Canonical rule:** The Python `claude-agent-sdk` is the canonical reference. This C++ port is expected to track its behavior and API (currently aligned with Python v0.1.18).
+
+Upstream sync checkpoints: `docs/upstream-sync.md`.
 
 ## License
 
diff --git a/docs/upstream-sync.md b/docs/upstream-sync.md
new file mode 100644
index 0000000..bacb7f3
--- /dev/null
+++ b/docs/upstream-sync.md
@@ -0,0 +1,11 @@
+# Upstream sync checkpoints
+
+This repo tracks the Python reference implementation:
+https://github.com/anthropics/claude-agent-sdk-python
+
+## 2026-01-07
+
+- Verified upstream commit: `51b5431`
+- Upstream change: bump packaged/bundled Claude Code CLI version constant from `2.0.73` to `2.1.1`
+- Porting impact: no C++ code changes required
+