diff --git a/CLAUDE.md b/CLAUDE.md
index cfc825b..a3a2278 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -5,7 +5,7 @@ High-performance Python HTTP client, API-compatible with httpx, powered by Rust'
 ## Features
 
 - **httpx API compatibility** — Drop-in replacement: `import requestx as httpx` works
-- **AI SDK compatible** — Works with OpenAI, Anthropic SDKs via `http_client=requestx.Client()`
+- **AI SDK compatible** — Works with OpenAI, Anthropic SDKs via `http_client=requestx.Client()` or `AsyncClient`
 - **High performance** — Rust-powered with GIL-free I/O, SIMD JSON (sonic-rs), zero-copy bytes
 - **Full async support** — Tokio runtime for true concurrent multiplexing
 - **Standards compliant** — WHATWG URL, RFC 2388 (multipart), RFC 7616 (digest auth), HTTP/2
@@ -189,9 +189,9 @@ let mut headers = Vec::with_capacity(response.headers().len());
 ```
 
 ### 7. SDK Compatibility
-- requestx patches `type.__instancecheck__` at import to pass httpx.Client isinstance checks
+- requestx patches `builtins.isinstance` at import to pass httpx.Client isinstance checks
 - This enables AI SDK compatibility (OpenAI, Anthropic accept requestx.Client)
-- Patch is global but detection is narrow (class + module name matching)
+- Patch is global but detection is narrow (checks `__name__` == "Client"/"AsyncClient" and `__module__` starts with "requestx")
 
 ## Don't
 
diff --git a/python/requestx/_client.py b/python/requestx/_client.py
index 3c39038..526ddbd 100644
--- a/python/requestx/_client.py
+++ b/python/requestx/_client.py
@@ -352,7 +352,15 @@ def build_request(self, method, url, **kwargs):
             else:
                 kwargs["params"] = self._params
 
-        rust_request = self._client.build_request(method, merged_url, **kwargs)
+        # Filter to only parameters supported by Rust build_request
+        # Rust signature: (method, url, *, content=None, data=None, files=None, json=None, params=None, headers=None, cookies=None)
+        # Note: timeout and extensions are httpx API parameters but not supported by Rust
+        supported_kwargs = {}
+        for key in ["content", "data", "files", "json", "params", "headers", "cookies"]:
+            if key in kwargs and kwargs[key] is not None:
+                supported_kwargs[key] = kwargs[key]
+
+        rust_request = self._client.build_request(method, merged_url, **supported_kwargs)
         # Create a wrapper that delegates to the Rust request but has our headers proxy
         wrapped = _WrappedRequest(rust_request, sync_stream=sync_stream)
         # Link the stream back to the owner for consumption tracking