diff --git a/run_agent.py b/run_agent.py
index f2f3379e0d78e..1d3464ab90f47 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -9980,13 +9980,14 @@ def _build_assistant_message(self, assistant_message, finish_reason: str) -> dic
     def _needs_thinking_reasoning_pad(self) -> bool:
         """Return True when the active provider enforces reasoning_content echo-back.
 
-        DeepSeek v4 thinking and Kimi / Moonshot thinking both reject replays
-        of assistant tool-call messages that omit ``reasoning_content`` (refs
-        #15250, #17400).
+        DeepSeek v4 thinking, Kimi / Moonshot thinking, and Xiaomi MiMo
+        thinking all reject replays of assistant tool-call messages that
+        omit ``reasoning_content`` (refs #15250, #17400, xiaomi).
         """
         return (
             self._needs_deepseek_tool_reasoning()
             or self._needs_kimi_tool_reasoning()
+            or self._needs_xiaomi_tool_reasoning()
         )
 
     def _needs_kimi_tool_reasoning(self) -> bool:
@@ -10018,6 +10019,20 @@ def _needs_deepseek_tool_reasoning(self) -> bool:
             or base_url_host_matches(self.base_url, "api.deepseek.com")
         )
 
+    def _needs_xiaomi_tool_reasoning(self) -> bool:
+        """Return True when the current provider is Xiaomi MiMo thinking mode.
+
+        Xiaomi MiMo thinking mode requires ``reasoning_content`` on every
+        assistant tool-call message; omitting it causes the next replay to
+        fail with HTTP 400 ("The reasoning_content in the thinking mode
+        must be passed back to the API").
+        """
+        provider = (self.provider or "").lower()
+        return (
+            provider == "xiaomi"
+            or base_url_host_matches(self.base_url, "xiaomimimo.com")
+        )
+
     def _copy_reasoning_content_for_api(self, source_msg: dict, api_msg: dict) -> None:
         """Copy provider-facing reasoning fields onto an API replay message."""
         if source_msg.get("role") != "assistant":