diff --git a/tests/test_list_content_compat.py b/tests/test_list_content_compat.py
new file mode 100644
index 00000000..eddca298
--- /dev/null
+++ b/tests/test_list_content_compat.py
@@ -0,0 +1,166 @@
+"""Tests for list-shaped chat-completions content from OpenAI-compatible gateways.
+
+Reasoning models behind some OpenAI-compatible endpoints return assistant
+content as a list of content blocks (``thinking`` + ``text``) instead of a
+plain string. The OpenAI client constructs its models without validating that
+field, and the SDK then crashes on ``ResponseOutputText``/``ResponseTextDeltaEvent``
+validation. ``chat_content_compat.install()`` flattens the text blocks before
+the SDK consumes them; a local gateway that answers with list-shaped content
+proves both the non-streaming and the streaming path work end to end.
+"""
+
+from __future__ import annotations
+
+import json
+import threading
+from http.server import BaseHTTPRequestHandler, HTTPServer
+from typing import TYPE_CHECKING, Any
+
+import pytest
+from agents.model_settings import ModelSettings
+from agents.models.interface import ModelTracing
+from agents.models.openai_chatcompletions import OpenAIChatCompletionsModel
+from openai import AsyncOpenAI
+from openai.types.responses import (
+    ResponseCompletedEvent,
+    ResponseOutputMessage,
+    ResponseOutputText,
+    ResponseTextDeltaEvent,
+)
+
+from strix.llm.chat_content_compat import install as install_content_compat
+
+
+if TYPE_CHECKING:
+    from collections.abc import AsyncIterator, Iterator
+
+install_content_compat()
+
+
+def _list_content_completion() -> dict[str, Any]:
+    return {
+        "id": "chatcmpl-1",
+        "object": "chat.completion",
+        "created": 0,
+        "model": "gw-model",
+        "choices": [
+            {
+                "index": 0,
+                "finish_reason": "stop",
+                "message": {
+                    "role": "assistant",
+                    "content": [
+                        {"type": "thinking", "thinking": "considering the request"},
+                        {"type": "text", "text": "OK"},
+                    ],
+                },
+            }
+        ],
+        "usage": {"prompt_tokens": 5, "completion_tokens": 3, "total_tokens": 8},
+    }
+
+
+def _list_content_chunks() -> list[dict[str, Any]]:
+    def chunk(delta: dict[str, Any], finish_reason: str | None = None) -> dict[str, Any]:
+        return {
+            "id": "chatcmpl-2",
+            "object": "chat.completion.chunk",
+            "created": 0,
+            "model": "gw-model",
+            "choices": [{"index": 0, "delta": delta, "finish_reason": finish_reason}],
+        }
+
+    return [
+        chunk({"role": "assistant"}),
+        chunk({"content": [{"type": "thinking", "thinking": "hmm"}]}),
+        chunk({"content": [{"type": "text", "text": "OK"}]}),
+        chunk({}, "stop"),
+    ]
+
+
+class _Handler(BaseHTTPRequestHandler):
+    """A gateway whose assistant content arrives as a list of content blocks."""
+
+    def log_message(self, *args: Any) -> None:
+        pass
+
+    def do_POST(self) -> None:
+        length = int(self.headers.get("Content-Length", 0))
+        body = json.loads(self.rfile.read(length) or b"{}")
+        if body.get("stream"):
+            payload = "".join(f"data: {json.dumps(c)}\n\n" for c in _list_content_chunks())
+            payload += "data"
+            payload_bytes = payload.encode()
+            self.send_response(200)
+            self.send_header("Content-Type", "text/event-stream")
+        else:
+            payload_bytes = json.dumps(_list_content_completion()).encode()
+            self.send_response(200)
+            self.send_header("Content-Type", "application/json")
+        self.send_header("Content-Length", str(len(payload_bytes)))
+        self.end_headers()
+        self.wfile.write(payload_bytes)
+
+
+@pytest.fixture
+def gateway_url() -> Iterator[str]:
+    server = HTTPServer(("127.0.0.1", 0), _Handler)
+    thread = threading.Thread(target=server.serve_forever, daemon=True)
+    thread.start()
+    try:
+        yield f"http://127.0.0.1:{server.server_address[1]}/v1"
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+def _model(base_url: str) -> OpenAIChatCompletionsModel:
+    client = AsyncOpenAI(api_key="tok", base_url=base_url)
+    return OpenAIChatCompletionsModel(model="gw-model", openai_client=client)
+
+
+def _call_kwargs() -> dict[str, Any]:
+    return {
+        "system_instructions": "s",
+        "input": "hi",
+        "model_settings": ModelSettings(),
+        "tools": [],
+        "output_schema": None,
+        "handoffs": [],
+        "tracing": ModelTracing.DISABLED,
+        "previous_response_id": None,
+        "conversation_id": None,
+        "prompt": None,
+    }
+
+
+async def _drain(gen: AsyncIterator[Any]) -> list[Any]:
+    return [event async for event in gen]
+
+
+async def test_get_response_flattens_list_content(gateway_url: str) -> None:
+    response = await _model(gateway_url).get_response(**_call_kwargs())
+
+    message = response.output[0]
+    assert isinstance(message, ResponseOutputMessage)
+    text = message.content[0]
+    assert isinstance(text, ResponseOutputText)
+    assert text.text == "OK"
+
+    assert response.usage is not None
+    assert response.usage.total_tokens == 8
+
+
+async def test_stream_response_flattens_list_content_deltas(gateway_url: str) -> None:
+    events = await _drain(_model(gateway_url).stream_response(**_call_kwargs()))
+
+    deltas = [e for e in events if isinstance(e, ResponseTextDeltaEvent)]
+    assert [d.delta for d in deltas] == ["OK"]
+
+    completed = events[-1]
+    assert isinstance(completed, ResponseCompletedEvent)
+    message = completed.response.output[0]
+    assert isinstance(message, ResponseOutputMessage)
+    text = message.content[0]
+    assert isinstance(text, ResponseOutputText)
+    assert text.text == "OK"