diff --git a/src/agents/models/chatcmpl_converter.py b/src/agents/models/chatcmpl_converter.py
index 0ece1664b..f17e8f126 100644
--- a/src/agents/models/chatcmpl_converter.py
+++ b/src/agents/models/chatcmpl_converter.py
@@ -480,7 +480,20 @@ def ensure_assistant_message() -> ChatCompletionAssistantMessageParam:
                 # If we have pending thinking blocks, use them as the content
                 # This is required for Anthropic API tool calls with interleaved thinking
                 if pending_thinking_blocks:
-                    asst["content"] = pending_thinking_blocks  # type: ignore
+                    # If there is a text content, save it to append after thinking blocks
+                    # content type is Union[str, Iterable[ContentArrayOfContentPart], None]
+                    if "content" in asst and isinstance(asst["content"], str):
+                        text_content = ChatCompletionContentPartTextParam(
+                            text=asst["content"], type="text"
+                        )
+                        asst["content"] = [text_content]
+
+                    if "content" not in asst or asst["content"] is None:
+                        asst["content"] = []
+
+                    # Thinking blocks MUST come before any other content
+                    # We ignore type errors because pending_thinking_blocks is not openai standard
+                    asst["content"] = pending_thinking_blocks + asst["content"]  # type: ignore
                     pending_thinking_blocks = None  # Clear after using
 
                 tool_calls = list(asst.get("tool_calls", []))
diff --git a/tests/test_anthropic_thinking_blocks.py b/tests/test_anthropic_thinking_blocks.py
index 35446efe4..8fbc59833 100644
--- a/tests/test_anthropic_thinking_blocks.py
+++ b/tests/test_anthropic_thinking_blocks.py
@@ -217,20 +217,27 @@ def test_anthropic_thinking_blocks_with_tool_calls():
         "Signature should be preserved in thinking block"
     )
 
-    first_content = content[1]
-    assert first_content.get("type") == "thinking", (
+    second_content = content[1]
+    assert second_content.get("type") == "thinking", (
         f"Second content must be 'thinking' type for Anthropic compatibility, "
-        f"but got '{first_content.get('type')}'"
+        f"but got '{second_content.get('type')}'"
     )
     expected_thinking = "We should use the city Tokyo as the city."
-    assert first_content.get("thinking") == expected_thinking, (
+    assert second_content.get("thinking") == expected_thinking, (
         "Thinking content should be preserved"
     )
     # Signature should also be preserved
-    assert first_content.get("signature") == "TestSignature456", (
+    assert second_content.get("signature") == "TestSignature456", (
         "Signature should be preserved in thinking block"
     )
 
+    last_content = content[2]
+    assert last_content.get("type") == "text", (
+        f"First content must be 'text' type but got '{last_content.get('type')}'"
+    )
+    expected_text = "I'll check the weather for you."
+    assert last_content.get("text") == expected_text, "Content text should be preserved"
+
     # Verify tool calls are preserved
     tool_calls = assistant_msg.get("tool_calls", [])
     assert len(cast(list[Any], tool_calls)) == 1, "Tool calls should be preserved"