diff --git a/python/packages/anthropic/agent_framework_anthropic/_chat_client.py b/python/packages/anthropic/agent_framework_anthropic/_chat_client.py
index c1d1ac26c4..5f3dfa83c5 100644
--- a/python/packages/anthropic/agent_framework_anthropic/_chat_client.py
+++ b/python/packages/anthropic/agent_framework_anthropic/_chat_client.py
@@ -455,7 +455,13 @@ def _prepare_options(
             # Add the structured outputs beta flag
             run_options["betas"].add(STRUCTURED_OUTPUTS_BETA_FLAG)
 
-        run_options.update(kwargs)
+        # Filter out framework kwargs that should not be passed to the Anthropic API.
+        # This includes underscore-prefixed internal objects (like _function_middleware_pipeline)
+        # and framework kwargs like 'thread' and 'middleware'.
+        filtered_kwargs = {
+            k: v for k, v in kwargs.items() if not k.startswith("_") and k not in {"thread", "middleware"}
+        }
+        run_options.update(filtered_kwargs)
         return run_options
 
     def _prepare_betas(self, options: Mapping[str, Any]) -> set[str]:
diff --git a/python/packages/anthropic/tests/test_anthropic_client.py b/python/packages/anthropic/tests/test_anthropic_client.py
index 5df7f585f3..75c2144258 100644
--- a/python/packages/anthropic/tests/test_anthropic_client.py
+++ b/python/packages/anthropic/tests/test_anthropic_client.py
@@ -479,6 +479,36 @@ async def test_prepare_options_with_top_p(mock_anthropic_client: MagicMock) -> N
     assert run_options["top_p"] == 0.9
 
 
+async def test_prepare_options_filters_internal_kwargs(mock_anthropic_client: MagicMock) -> None:
+    """Test _prepare_options filters internal framework kwargs.
+
+    Internal kwargs like _function_middleware_pipeline, thread, and middleware
+    should be filtered out before being passed to the Anthropic API.
+    """
+    chat_client = create_test_anthropic_client(mock_anthropic_client)
+
+    messages = [ChatMessage(role="user", text="Hello")]
+    chat_options: ChatOptions = {}
+
+    # Simulate internal kwargs that get passed through the middleware pipeline
+    internal_kwargs = {
+        "_function_middleware_pipeline": object(),
+        "_chat_middleware_pipeline": object(),
+        "_any_underscore_prefixed": object(),
+        "thread": object(),
+        "middleware": [object()],
+    }
+
+    run_options = chat_client._prepare_options(messages, chat_options, **internal_kwargs)
+
+    # Internal kwargs should be filtered out
+    assert "_function_middleware_pipeline" not in run_options
+    assert "_chat_middleware_pipeline" not in run_options
+    assert "_any_underscore_prefixed" not in run_options
+    assert "thread" not in run_options
+    assert "middleware" not in run_options
+
+
 # Response Processing Tests
 
 
diff --git a/python/packages/core/tests/workflow/test_sub_workflow.py b/python/packages/core/tests/workflow/test_sub_workflow.py
index c413190a24..33333d2906 100644
--- a/python/packages/core/tests/workflow/test_sub_workflow.py
+++ b/python/packages/core/tests/workflow/test_sub_workflow.py
@@ -599,7 +599,7 @@ async def test_sub_workflow_checkpoint_restore_no_duplicate_requests() -> None:
 
     # Get checkpoint
     checkpoints = await storage.list_checkpoints(workflow1.id)
-    checkpoint_id = max(checkpoints, key=lambda cp: cp.timestamp).checkpoint_id
+    checkpoint_id = max(checkpoints, key=lambda cp: cp.iteration_count).checkpoint_id
 
     # Step 2: Resume workflow from checkpoint
     workflow2 = _build_checkpoint_test_workflow(storage)