diff --git a/strix/config/models.py b/strix/config/models.py
index 27e47a37..60ea0eb1 100644
--- a/strix/config/models.py
+++ b/strix/config/models.py
@@ -40,7 +40,7 @@ from strix.config import codex
 from strix.config.loader import load_settings
 from strix.config.tool_call_ids import TurnCallIdRewriter, dedupe_input
 from strix.config.tool_call_limits import TurnToolCallLimiter
-from strix.llm import request_log
+from strix.llm import chat_content_compat, request_log
 
 
 if TYPE_CHECKING:
@@ -664,6 +664,7 @@ def configure_sdk_model_defaults(settings: Settings) -> None:
     llm = settings.llm
     set_tracing_disabled(True)
     request_log.install()
+    chat_content_compat.install()
     if codex.subscription_model(llm.model):
         return
     _configure_litellm_compatibility()
diff --git a/strix/llm/chat_content_compat.py b/strix/llm/chat_content_compat.py
new file mode 100644
index 00000000..68e9fe56
--- /dev/null
+++ b/strix/llm/chat_content_compat.py
@@ -0,0 +1,96 @@
+"""Flatten list-shaped chat-completions content from OpenAI-compatible providers.
+
+Reasoning models behind OpenAI-compatible endpoints sometimes return the
+assistant content as a list of content blocks (for example
+``[{"type": "thinking", ...}, {"type": "text", "text": "OK"}]``) instead of a
+plain string.
+
+``install()`` wraps the two SDK entry points that consume chat-completions
+content, flattening list-shaped ``message.content`` and ``delta.content`` into
+the concatenated ``text`` blocks before the SDK sees them. Non-text blocks
+(e.g. ``thinking``) and unknown block types are ignored.
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import TYPE_CHECKING, Any, cast
+
+
+logger = logging.getLogger(__name__)
+
+if TYPE_CHECKING:
+    from collections.abc import AsyncIterator
+
+
+def _flatten_list_content(content: object) -> Any:
+    """Concatenate the ``text`` blocks of list-shaped content; pass anything else through."""
+    if not isinstance(content, list):
+        return content
+    texts: list[str] = []
+    blocks = cast("list[Any]", content)  # type: ignore[redundant-cast]
+    for part in blocks:
+        if not isinstance(part, dict):
+            continue
+        block = cast("dict[str, Any]", part)
+        if block.get("type") == "text":
+            text = block.get("text")
+            if isinstance(text, str):
+                texts.append(text)
+    return "".join(texts)
+
+
+async def _flatten_chunk_stream(stream: AsyncIterator[Any]) -> AsyncIterator[Any]:
+    async for chunk in stream:
+        choices: list[Any] = getattr(chunk, "choices", None) or []
+        for choice in choices:
+            delta: Any = getattr(choice, "delta", None)
+            content = getattr(delta, "content", None)
+            if delta is not None and isinstance(content, list):
+                blocks = cast("list[Any]", content)  # type: ignore[redundant-cast]
+                choice.delta = delta.model_copy(update={"content": _flatten_list_content(blocks)})
+        yield chunk
+
+
+_installed = False
+
+
+def install() -> None:
+    """Wrap the SDK chat-completions content entry points (idempotent)."""
+    global _installed  # noqa: PLW0603
+    if _installed:
+        return
+    _installed = True
+    try:
+        _install_wrappers()
+    except Exception:  # noqa: BLE001 - an SDK layout change degrades to the stock behavior
+        logger.warning("could not wrap the SDK chat-completions content handling", exc_info=True)
+
+
+def _install_wrappers() -> None:
+    from agents.models import chatcmpl_converter
+    from agents.models.chatcmpl_stream_handler import ChatCmplStreamHandler
+
+    # 0.19.0 names it Converter; later 0.19.x releases renamed it ChatCmplConverter.
+    converter_cls = getattr(chatcmpl_converter, "ChatCmplConverter", None) or (
+        chatcmpl_converter.Converter
+    )
+
+    convert = converter_cls.__dict__["message_to_output_items"].__func__
+    handle_stream = ChatCmplStreamHandler.__dict__["handle_stream"].__func__
+
+    def message_to_output_items(cls: Any, message: Any, *args: Any, **kwargs: Any) -> Any:
+        content = getattr(message, "content", None)
+        if isinstance(content, list):
+            blocks = cast("list[Any]", content)  # type: ignore[redundant-cast]
+            message = message.model_copy(update={"content": _flatten_list_content(blocks)})
+        return convert(cls, message, *args, **kwargs)
+
+    def handle_list_content_stream(
+        cls: Any, response: Any, stream: AsyncIterator[Any], *args: Any, **kwargs: Any
+    ) -> Any:
+        return handle_stream(cls, response, _flatten_chunk_stream(stream), *args, **kwargs)
+
+    converter_cls.message_to_output_items = classmethod(message_to_output_items)  # type: ignore[method-assign]
+    ChatCmplStreamHandler.handle_stream = classmethod(handle_list_content_stream)  # type: ignore[assignment]
+    _installed = True