diff --git a/astrbot/core/provider/sources/openai_source.py b/astrbot/core/provider/sources/openai_source.py
index 117cfb4922..1585846987 100644
--- a/astrbot/core/provider/sources/openai_source.py
+++ b/astrbot/core/provider/sources/openai_source.py
@@ -550,8 +550,9 @@ def _is_empty(content: Any) -> bool:
 
             content = msg.get("content")
             tool_calls = msg.get("tool_calls")
+            reasoning_content = msg.get("reasoning_content")
 
-            if _is_empty(content) and not tool_calls:
+            if _is_empty(content) and not tool_calls and not reasoning_content:
                 logger.warning(f"过滤第 {idx} 条空 assistant 消息 (无工具调用)")
                 continue
 
@@ -1015,6 +1016,16 @@ def _finally_convert_payload(self, payloads: dict) -> None:
             model in deepseek_reasoning_models
             or "api.deepseek.com" in self.client.base_url.host
         )
+        # MiMo 推理模型（MiMo-V2.5-Pro / MiMo-V2.5 / MiMo-V2-Pro / MiMo-V2-Omni / MiMo-V2-Flash）
+        # 要求 assistant 历史消息必须回传 reasoning_content，否则返回 400
+        mimo_reasoning_models = {
+            "mimo-v2.5-pro",
+            "mimo-v2.5",
+            "mimo-v2-pro",
+            "mimo-v2-omni",
+            "mimo-v2-flash",
+        }
+        is_mimo_reasoning = model in mimo_reasoning_models
         for message in payloads.get("messages", []):
             if message.get("role") == "assistant" and isinstance(
                 message.get("content"), list
@@ -1043,6 +1054,15 @@ def _finally_convert_payload(self, payloads: dict) -> None:
                 # history messages, even when the reasoning content is empty.
                 message["reasoning_content"] = ""
 
+            if (
+                message.get("role") == "assistant"
+                and is_mimo_reasoning
+                and "reasoning_content" not in message
+            ):
+                # MiMo 推理模型要求 assistant 历史消息回传 reasoning_content，
+                # 缺失时 API 返回 400。参见 MiMo 官方文档。
+                message["reasoning_content"] = ""
+
             # Gemini 的 function_response 要求 google.protobuf.Struct（即 JSON 对象），
             # 纯文本会触发 400 Invalid argument，需要包一层 JSON。
             if is_gemini and message.get("role") == "tool":
diff --git a/tests/test_openai_source.py b/tests/test_openai_source.py
index 950e2ea162..a9409bb34d 100644
--- a/tests/test_openai_source.py
+++ b/tests/test_openai_source.py
@@ -1786,3 +1786,126 @@ async def fake_create(**kwargs):
         assert messages[1] == {"role": "user", "content": "again"}
     finally:
         await provider.terminate()
+
+
+# ===== MiMo reasoning_content 回传测试 =====
+
+MIMO_REASONING_MODELS = [
+    "mimo-v2.5-pro",
+    "mimo-v2.5",
+    "mimo-v2-pro",
+    "mimo-v2-omni",
+    "mimo-v2-flash",
+]
+
+MIMO_NON_REASONING_MODELS = [
+    "mimo-v2-tts",
+    "mimo-v2.5-tts",
+    "mimo-v2.5-tts-voicedesign",
+]
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("model", MIMO_REASONING_MODELS)
+async def test_mimo_reasoning_model_adds_empty_reasoning_content(model: str):
+    """MiMo 推理模型：assistant 消息缺少 reasoning_content 时自动补空字符串"""
+    provider = _make_provider()
+    try:
+        payloads = {
+            "model": model,
+            "messages": [
+                {"role": "user", "content": "hello"},
+                {
+                    "role": "assistant",
+                    "content": "I will help with that.",
+                },
+            ],
+        }
+
+        provider._finally_convert_payload(payloads)
+
+        assistant = payloads["messages"][1]
+        assert assistant["reasoning_content"] == ""
+    finally:
+        await provider.terminate()
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("model", MIMO_NON_REASONING_MODELS)
+async def test_mimo_non_reasoning_model_does_not_add_reasoning_content(model: str):
+    """MiMo 非推理模型（TTS 等）：不应自动注入 reasoning_content"""
+    provider = _make_provider()
+    try:
+        payloads = {
+            "model": model,
+            "messages": [
+                {"role": "user", "content": "hello"},
+                {
+                    "role": "assistant",
+                    "content": "speaking...",
+                },
+            ],
+        }
+
+        provider._finally_convert_payload(payloads)
+
+        assistant = payloads["messages"][1]
+        assert "reasoning_content" not in assistant
+    finally:
+        await provider.terminate()
+
+
+@pytest.mark.asyncio
+async def test_mimo_reasoning_preserves_existing_reasoning_content():
+    """已有 reasoning_content 的 assistant 消息不会被覆盖"""
+    provider = _make_provider()
+    try:
+        payloads = {
+            "model": "mimo-v2.5-pro",
+            "messages": [
+                {"role": "user", "content": "hello"},
+                {
+                    "role": "assistant",
+                    "content": [
+                        {"type": "think", "think": "let me think..."},
+                        {"type": "text", "text": "here is the answer"},
+                    ],
+                },
+            ],
+        }
+
+        provider._finally_convert_payload(payloads)
+
+        assistant = payloads["messages"][1]
+        assert assistant["reasoning_content"] == "let me think..."
+        assert assistant["content"] == [{"type": "text", "text": "here is the answer"}]
+    finally:
+        await provider.terminate()
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("model", MIMO_REASONING_MODELS)
+async def test_mimo_filter_preserves_reasoning_only_assistant_message(model: str):
+    """仅有 reasoning_content 的 assistant 消息不会被 _sanitize 过滤掉"""
+    provider = _make_provider()
+    try:
+        payloads = {
+            "model": model,
+            "messages": [
+                {"role": "user", "content": "hello"},
+                {
+                    "role": "assistant",
+                    "content": "",
+                    "reasoning_content": "thinking about the answer...",
+                },
+                {"role": "user", "content": "world"},
+            ],
+        }
+
+        provider._sanitize_assistant_messages(payloads)
+
+        messages = payloads["messages"]
+        assert len(messages) == 3, "含 reasoning_content 的消息不应被过滤"
+        assert messages[1]["reasoning_content"] == "thinking about the answer..."
+    finally:
+        await provider.terminate()