--- agent/anthropic_adapter.py.orig	2026-09-24 10:08:47 UTC
+++ agent/anthropic_adapter.py
@@ -338,9 +338,37 @@ def _attribution_headers() -> Dict[str, str]:
     }
 
 
+_SDK_HTTPX_MOD = None
+
+
+def _sdk_httpx():
+    """The httpx module the installed anthropic SDK is built against.
+
+    anthropic 1.x moved its HTTP stack to ``httpx2``; objects crossing the SDK boundary
+    (``Timeout``, ``http_client``) must come from the same module or the SDK rejects them at
+    request time. Same split ``tools/mcp_tool.py:sdk_httpx()`` handles for mcp 1.x/2.x.
+    """
+    global _SDK_HTTPX_MOD
+    if _SDK_HTTPX_MOD is not None:
+        return _SDK_HTTPX_MOD
+    try:
+        from anthropic import _base_client as _bc
+        _SDK_HTTPX_MOD = getattr(_bc, "httpx2", None) or getattr(_bc, "httpx", None)
+    except ImportError:
+        _SDK_HTTPX_MOD = None
+    if _SDK_HTTPX_MOD is None:
+        try:
+            import httpx2 as _fallback
+        except ImportError:
+            import httpx as _fallback  # type: ignore[no-redef]
+        _SDK_HTTPX_MOD = _fallback
+    return _SDK_HTTPX_MOD
+
+
 def _client_timeout(timeout):
-    """httpx.Timeout with the caller's read timeout (default 900s) and a 10s connect."""
-    from httpx import Timeout
+    """httpx.Timeout with the caller's read timeout (default 900s) and a 10s connect.
+    Timeout comes from the SDK's own httpx flavour (see ``_sdk_httpx``)."""
+    Timeout = _sdk_httpx().Timeout
     read = timeout if (isinstance(timeout, (int, float)) and timeout > 0) else 900.0
     return Timeout(timeout=float(read), connect=10.0)
 
@@ -372,7 +400,9 @@ def _build_anthropic_client_with_bearer_hook(
     normalize_proxy_env_vars()
     from agent.azure_identity_adapter import build_bearer_http_client
     normalized_base_url, kwargs = _base_client_kwargs(base_url, timeout)
-    kwargs["http_client"] = build_bearer_http_client(token_provider, timeout=kwargs["timeout"])
+    kwargs["http_client"] = build_bearer_http_client(
+        token_provider, httpx_mod=_sdk_httpx(), timeout=kwargs["timeout"]
+    )
     kwargs["auth_token"] = "entra-id-bearer-via-http-hook"
     betas = _common_betas_for_base_url(normalized_base_url, drop_context_1m_beta=drop_context_1m_beta)
     from agent.anthropic_credentials import anthropic_route_is_oauth