diff --git a/app-instance/backend/beaver/engine/providers/litellm.py b/app-instance/backend/beaver/engine/providers/litellm.py
index fab3ded..7fe2e7f 100644
--- a/app-instance/backend/beaver/engine/providers/litellm.py
+++ b/app-instance/backend/beaver/engine/providers/litellm.py
@@ -3,9 +3,11 @@
 from __future__ import annotations
 
 from contextlib import contextmanager
+from ipaddress import ip_address
 import json
 import os
 from typing import Any
+from urllib.parse import urlsplit
 
 from .base import LLMProvider, LLMResponse, ToolCallRequest
 from .registry import find_by_model, find_by_name, find_gateway
@@ -26,6 +28,23 @@ except ModuleNotFoundError:  # pragma: no cover
 _ALLOWED_MSG_KEYS = frozenset({"role", "content", "tool_calls", "tool_call_id", "name", "reasoning_content"})
 
 
+def _looks_like_local_vllm_api_base(api_base: str | None) -> bool:
+    if not api_base:
+        return False
+    lowered = api_base.lower()
+    if "vllm" in lowered or "localhost" in lowered:
+        return True
+
+    host = urlsplit(lowered).hostname or ""
+    if host in {"127.0.0.1", "::1", "0.0.0.0"}:
+        return True
+    try:
+        parsed_host = ip_address(host)
+    except ValueError:
+        return False
+    return parsed_host.is_private or parsed_host.is_loopback
+
+
 class LiteLLMProvider(LLMProvider):
     """通过 LiteLLM 统一访问大多数 provider。"""
 
@@ -200,10 +219,12 @@ class LiteLLMProvider(LLMProvider):
         kwargs["extra_body"] = extra_body
 
     def _uses_mistral_reasoning_parser(self, original_model: str, resolved_model: str) -> bool:
-        if self.provider_name != "vllm":
-            return False
         model_names = f"{original_model} {resolved_model}".lower()
-        return "mistral" in model_names
+        if "mistral" not in model_names:
+            return False
+        if self.provider_name == "vllm":
+            return True
+        return self.provider_name in {"openai", "custom"} and _looks_like_local_vllm_api_base(self.api_base)
 
     async def chat(
         self,
diff --git a/app-instance/backend/tests/unit/test_litellm_thinking_mode.py b/app-instance/backend/tests/unit/test_litellm_thinking_mode.py
index 1700d87..8a701ea 100644
--- a/app-instance/backend/tests/unit/test_litellm_thinking_mode.py
+++ b/app-instance/backend/tests/unit/test_litellm_thinking_mode.py
@@ -253,6 +253,91 @@ def test_mistral_vllm_omits_reasoning_body_when_thinking_mode_is_unspecified(
     assert "extra_body" not in captured
 
 
+def test_mistral_openai_compatible_private_vllm_uses_reasoning_effort(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    captured: dict = {}
+
+    class Message:
+        content = "ok"
+        reasoning_content = None
+        tool_calls = []
+
+    class Choice:
+        message = Message()
+        finish_reason = "stop"
+
+    class Response:
+        choices = [Choice()]
+        usage = None
+
+    async def fake_acompletion(**kwargs):
+        captured.update(kwargs)
+        return Response()
+
+    monkeypatch.setattr("beaver.engine.providers.litellm.acompletion", fake_acompletion)
+    monkeypatch.setattr("beaver.engine.providers.litellm.litellm", SimpleNamespace())
+
+    provider = LiteLLMProvider(
+        api_key="EMPTY",
+        api_base="http://172.19.207.103/v1",
+        default_model="Mistral-Medium-3.5-128B",
+        provider_name="openai",
+    )
+    asyncio.run(
+        provider.chat(
+            [{"role": "user", "content": "reply ok"}],
+            model="Mistral-Medium-3.5-128B",
+            thinking_enabled=False,
+        )
+    )
+
+    assert captured["extra_body"] == {"reasoning_effort": "none"}
+    assert "chat_template_kwargs" not in captured["extra_body"]
+    assert "thinking" not in captured["extra_body"]
+
+
+def test_mistral_openai_compatible_private_vllm_omits_body_when_unspecified(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    captured: dict = {}
+
+    class Message:
+        content = "ok"
+        reasoning_content = None
+        tool_calls = []
+
+    class Choice:
+        message = Message()
+        finish_reason = "stop"
+
+    class Response:
+        choices = [Choice()]
+        usage = None
+
+    async def fake_acompletion(**kwargs):
+        captured.update(kwargs)
+        return Response()
+
+    monkeypatch.setattr("beaver.engine.providers.litellm.acompletion", fake_acompletion)
+    monkeypatch.setattr("beaver.engine.providers.litellm.litellm", SimpleNamespace())
+
+    provider = LiteLLMProvider(
+        api_key="EMPTY",
+        api_base="http://172.19.207.103/v1",
+        default_model="Mistral-Medium-3.5-128B",
+        provider_name="openai",
+    )
+    asyncio.run(
+        provider.chat(
+            [{"role": "user", "content": "reply ok"}],
+            model="Mistral-Medium-3.5-128B",
+        )
+    )
+
+    assert "extra_body" not in captured
+
+
 def test_litellm_provider_sanitizes_tool_call_arguments(monkeypatch: pytest.MonkeyPatch) -> None:
     captured: dict = {}