diff --git a/README.md b/README.md
index 64463d41..f901a45c 100644
--- a/README.md
+++ b/README.md
@@ -116,6 +116,7 @@ Lines starting with `,` enter internal command mode (`,help`, `,skill name=my-sk
 | `BUB_API_KEY`               | —                            | Provider key (optional with `bub login openai`)      |
 | `BUB_API_BASE`              | —                            | Custom provider endpoint                             |
 | `BUB_CLIENT_ARGS`           | —                            | JSON object forwarded to the underlying model client |
+| `BUB_COMPLETION_ARGS`       | —                            | JSON object forwarded to each completion call         |
 | `BUB_MAX_STEPS`             | `50`                         | Max tool-use loop iterations                         |
 | `BUB_MAX_TOKENS`            | `16384`                      | Max tokens per model call                            |
 | `BUB_MODEL_TIMEOUT_SECONDS` | —                            | Model call timeout (seconds)                         |
diff --git a/src/bub/builtin/model_runner.py b/src/bub/builtin/model_runner.py
index bd7365a6..fbbb4a71 100644
--- a/src/bub/builtin/model_runner.py
+++ b/src/bub/builtin/model_runner.py
@@ -92,14 +92,16 @@ async def completion_response(
         for index, (candidate, llm) in enumerate(clients):
             try:
                 streaming = llm.SUPPORTS_COMPLETION_STREAMING
-                return await llm.acompletion(
-                    model=candidate.model_id,
-                    messages=completion_messages,
-                    tools=tool_payloads,
-                    max_tokens=max_tokens if max_tokens is not None else self.settings.max_tokens,
-                    stream=streaming,
+                completion_kwargs = {
+                    **self.settings.completion_args,
                     **_extra_options(llm, stream=streaming),
-                )
+                    "model": candidate.model_id,
+                    "messages": completion_messages,
+                    "tools": tool_payloads,
+                    "max_tokens": max_tokens if max_tokens is not None else self.settings.max_tokens,
+                    "stream": streaming,
+                }
+                return cast("CompletionResult", await llm.acompletion(**completion_kwargs))
             except Exception as exc:
                 if completion_error is None:
                     completion_error = exc
diff --git a/src/bub/builtin/settings.py b/src/bub/builtin/settings.py
index 49d88389..b440d864 100644
--- a/src/bub/builtin/settings.py
+++ b/src/bub/builtin/settings.py
@@ -60,6 +60,7 @@ class AgentSettings(Settings):
     max_tokens: int = DEFAULT_MAX_TOKENS
     model_timeout_seconds: int | None = None
     client_args: dict[str, Any] = Field(default_factory=dict)
+    completion_args: dict[str, Any] = Field(default_factory=dict)
     verbose: int = Field(default=0, description="Verbosity level for logging. Higher means more verbose.", ge=0, le=2)
 
     @classmethod
@@ -79,9 +80,9 @@ def settings_customise_sources(
             file_secret_settings,
         )
 
-    @field_validator("client_args", mode="before")
+    @field_validator("client_args", "completion_args", mode="before")
     @classmethod
-    def default_client_args(cls, value: Any) -> Any:
+    def default_dict_args(cls, value: Any) -> Any:
         return {} if value is None else value
 
     def model_candidates(self, model: str) -> list[ModelCandidate]:
diff --git a/tests/test_builtin_model_runner.py b/tests/test_builtin_model_runner.py
index f60e4543..4dc1b4db 100644
--- a/tests/test_builtin_model_runner.py
+++ b/tests/test_builtin_model_runner.py
@@ -136,3 +136,36 @@ async def test_anthropic_prompt_caching_is_requested() -> None:
     assert llm.completion_kwargs["stream"] is True
     assert llm.completion_kwargs["cache_control"] == {"type": "ephemeral"}
     assert "stream_options" not in llm.completion_kwargs
+
+
+@pytest.mark.asyncio
+async def test_completion_args_are_forwarded_without_overriding_managed_args() -> None:
+    llm = _FakeStreamingOpenAIProvider()
+    runner = _FakeOpenAIModelRunner(
+        AgentSettings.model_construct(
+            model="openai:gpt-test",
+            max_tokens=100,
+            completion_args={
+                "reasoning_effort": "high",
+                "model": "ignored-model",
+                "max_tokens": 1,
+                "stream": False,
+                "stream_options": {"include_usage": False},
+            },
+        ),
+        llm,
+    )
+
+    await runner.completion_response(
+        model="gpt-test",
+        messages=[{"role": "user", "content": "hello"}],
+        tools=[],
+        max_tokens=42,
+    )
+
+    assert llm.completion_kwargs is not None
+    assert llm.completion_kwargs["reasoning_effort"] == "high"
+    assert llm.completion_kwargs["model"] == "gpt-test"
+    assert llm.completion_kwargs["max_tokens"] == 42
+    assert llm.completion_kwargs["stream"] is True
+    assert llm.completion_kwargs["stream_options"] == {"include_usage": True}
diff --git a/tests/test_settings.py b/tests/test_settings.py
index 6d3c6f63..02127a43 100644
--- a/tests/test_settings.py
+++ b/tests/test_settings.py
@@ -38,6 +38,7 @@ def test_settings_no_keys_return_none() -> None:
     assert settings.api_key is None
     assert settings.api_base is None
     assert settings.client_args == {}
+    assert settings.completion_args == {}
 
 
 def test_settings_provider_names_are_lowercased() -> None:
@@ -74,6 +75,8 @@ def test_settings_load_values_from_yaml(load_config) -> None:
   extra_headers:
     HTTP-Referer: https://openclaw.ai
     X-Title: OpenClaw
+completion_args:
+  reasoning_effort: high
 """.strip(),
         )
 
@@ -87,6 +90,7 @@ def test_settings_load_values_from_yaml(load_config) -> None:
     assert settings.client_args == {
         "extra_headers": {"HTTP-Referer": "https://openclaw.ai", "X-Title": "OpenClaw"},
     }
+    assert settings.completion_args == {"reasoning_effort": "high"}
 
 
 def test_env_settings_override_yaml(load_config) -> None:
@@ -106,6 +110,7 @@ def test_env_settings_override_yaml(load_config) -> None:
             "BUB_MODEL": "anthropic:claude-3-7-sonnet",
             "BUB_API_KEY": "sk-env",
             "BUB_CLIENT_ARGS": '{"extra_headers":{"HTTP-Referer":"https://env.example","X-Title":"Env App"}}',
+            "BUB_COMPLETION_ARGS": '{"reasoning_effort":"medium"}',
             "BUB_MAX_STEPS": "12",
         },
         clear=True,
@@ -119,12 +124,14 @@ def test_env_settings_override_yaml(load_config) -> None:
     assert settings.client_args == {
         "extra_headers": {"HTTP-Referer": "https://env.example", "X-Title": "Env App"},
     }
+    assert settings.completion_args == {"reasoning_effort": "medium"}
 
 
 def test_settings_client_args_can_be_disabled() -> None:
-    settings = _settings_with_env({"BUB_CLIENT_ARGS": "null"})
+    settings = _settings_with_env({"BUB_CLIENT_ARGS": "null", "BUB_COMPLETION_ARGS": "null"})
 
     assert settings.client_args == {}
+    assert settings.completion_args == {}
 
 
 def test_load_settings_returns_defaults_without_loaded_config() -> None:
diff --git a/website/src/content/docs/docs/reference/settings.mdx b/website/src/content/docs/docs/reference/settings.mdx
index cd5c9ef7..ce6a471c 100644
--- a/website/src/content/docs/docs/reference/settings.mdx
+++ b/website/src/content/docs/docs/reference/settings.mdx
@@ -48,6 +48,7 @@ class AgentSettings(Settings):
     max_tokens: int = DEFAULT_MAX_TOKENS  # 16384
     model_timeout_seconds: int | None = None
     client_args: dict[str, Any] = Field(default_factory=dict)
+    completion_args: dict[str, Any] = Field(default_factory=dict)
     verbose: int = Field(default=0, ge=0, le=2)
 ```
 
@@ -65,6 +66,7 @@ Loaded under the YAML root section.
 | `BUB_MAX_TOKENS` | `16384` | `max_tokens` | Maximum tokens per model call. |
 | `BUB_MODEL_TIMEOUT_SECONDS` | `null` | `model_timeout_seconds` | Per-call timeout in seconds. |
 | `BUB_CLIENT_ARGS` | `{}` | `client_args` | Extra kwargs passed to the underlying model client (JSON / dict). |
+| `BUB_COMPLETION_ARGS` | `{}` | `completion_args` | Extra kwargs passed to each completion call, e.g. `{"reasoning_effort":"high"}`. Bub-managed arguments take precedence. |
 | `BUB_VERBOSE` | `0` | `verbose` | Logging verbosity level (`0`–`2`). |
 
 Provider-specific defaults are gathered at startup by scanning `os.environ` for `^BUB_(.+)_(API_KEY|API_BASE)$` and lowercasing the captured provider name.
diff --git a/website/src/content/docs/zh-cn/docs/reference/settings.mdx b/website/src/content/docs/zh-cn/docs/reference/settings.mdx
index bef7297a..674a7a3b 100644
--- a/website/src/content/docs/zh-cn/docs/reference/settings.mdx
+++ b/website/src/content/docs/zh-cn/docs/reference/settings.mdx
@@ -48,6 +48,7 @@ class AgentSettings(Settings):
     max_tokens: int = DEFAULT_MAX_TOKENS  # 16384
     model_timeout_seconds: int | None = None
     client_args: dict[str, Any] = Field(default_factory=dict)
+    completion_args: dict[str, Any] = Field(default_factory=dict)
     verbose: int = Field(default=0, ge=0, le=2)
 ```
 
@@ -65,6 +66,7 @@ class AgentSettings(Settings):
 | `BUB_MAX_TOKENS` | `16384` | `max_tokens` | 单次模型调用的最大 token 数。 |
 | `BUB_MODEL_TIMEOUT_SECONDS` | `null` | `model_timeout_seconds` | 单次调用的超时秒数。 |
 | `BUB_CLIENT_ARGS` | `{}` | `client_args` | 传递给底层模型 client 的额外 kwargs(JSON / dict)。 |
+| `BUB_COMPLETION_ARGS` | `{}` | `completion_args` | 传递给每次 completion 调用的额外 kwargs,例如 `{"reasoning_effort":"high"}`;Bub 管理的参数优先。 |
 | `BUB_VERBOSE` | `0` | `verbose` | 日志详细级别(`0`–`2`)。 |
 
 启动时 `ProviderSpecificEnvSource` 会扫描 `os.environ` 中匹配 `^BUB_(.+)_(API_KEY|API_BASE)$` 的变量,把捕获到的 provider 名称小写后作为 key 收集。