diff --git a/backend/crates/gateway-api/src/openai/models.rs b/backend/crates/gateway-api/src/openai/models.rs
index 448881405..28a79e599 100644
--- a/backend/crates/gateway-api/src/openai/models.rs
+++ b/backend/crates/gateway-api/src/openai/models.rs
@@ -124,6 +124,7 @@ fn codex_model_json(profile: &PublicModelProfile, index: usize) -> Value {
         .iter()
         .any(|effort| effort != "none");
     let context_window = presentation.context_window_tokens();
+    let max_context_window = presentation.max_context_window_tokens();
     let input_modalities = if presentation.image_input() {
         vec!["text", "image"]
     } else {
@@ -173,7 +174,7 @@ fn codex_model_json(profile: &PublicModelProfile, index: usize) -> Value {
         "supports_parallel_tool_calls": presentation.parallel_tool_calls(),
         "supports_image_detail_original": presentation.image_detail_original(),
         "context_window": context_window,
-        "max_context_window": context_window,
+        "max_context_window": max_context_window,
         "effective_context_window_percent": 95,
         "experimental_supported_tools": [],
         "input_modalities": input_modalities,
diff --git a/backend/crates/gateway-api/tests/openai/models.rs b/backend/crates/gateway-api/tests/openai/models.rs
index 1960bc4b2..153b764f2 100644
--- a/backend/crates/gateway-api/tests/openai/models.rs
+++ b/backend/crates/gateway-api/tests/openai/models.rs
@@ -19,28 +19,55 @@ use super::{api_router, authenticated_client, authenticated_client_with_min_vers
 
 pub(super) struct ModelsExecution {
     client: AuthenticatedClient,
-    profiles: bool,
+    presentation: Option<ModelPresentation>,
 }
 
 impl ModelsExecution {
     pub(super) fn new() -> Arc<Self> {
         Arc::new(Self {
             client: authenticated_client("sk_models_test"),
-            profiles: false,
+            presentation: None,
         })
     }
 
     fn with_profiles() -> Arc<Self> {
+        Self::with_presentation(
+            ModelPresentation::new(
+                Some("Grok 4.5".to_owned()),
+                Some("xAI Grok 4.5 frontier model.".to_owned()),
+            )
+            .with_reasoning(
+                Some("medium".to_owned()),
+                ["low", "medium", "high", "xhigh"]
+                    .map(str::to_owned)
+                    .to_vec(),
+            )
+            .with_context_window_tokens(Some(500_000))
+            .with_max_context_window_tokens(Some(900_000))
+            .with_image_input(true)
+            .with_agent_tools(true, true)
+            .with_service_tiers(vec![
+                ModelServiceTier::new(
+                    "priority",
+                    "Fast",
+                    "Route the request through Codex fast mode.",
+                )
+                .with_speed_tier("fast"),
+            ]),
+        )
+    }
+
+    fn with_presentation(presentation: ModelPresentation) -> Arc<Self> {
         Arc::new(Self {
             client: authenticated_client("sk_models_test"),
-            profiles: true,
+            presentation: Some(presentation),
         })
     }
 
     fn with_cli_min() -> Arc<Self> {
         Arc::new(Self {
             client: authenticated_client_with_min_versions("sk_models_test", None, Some("0.40.0")),
-            profiles: false,
+            presentation: None,
         })
     }
 
@@ -51,7 +78,7 @@ impl ModelsExecution {
                 Some("26.825.51511"),
                 None,
             ),
-            profiles: false,
+            presentation: None,
         })
     }
 }
@@ -76,32 +103,12 @@ impl ExecutionService for ModelsExecution {
     }
 
     fn public_model_profiles(&self, _: &AuthenticatedClient) -> Vec<PublicModelProfile> {
-        if !self.profiles {
+        let Some(presentation) = &self.presentation else {
             return Vec::new();
-        }
+        };
         vec![PublicModelProfile::new(
             PublicModelId::new("grok-4.5").expect("model"),
-            ModelPresentation::new(
-                Some("Grok 4.5".to_owned()),
-                Some("xAI Grok 4.5 frontier model.".to_owned()),
-            )
-            .with_reasoning(
-                Some("medium".to_owned()),
-                ["low", "medium", "high", "xhigh"]
-                    .map(str::to_owned)
-                    .to_vec(),
-            )
-            .with_context_window_tokens(Some(500_000))
-            .with_image_input(true)
-            .with_agent_tools(true, true)
-            .with_service_tiers(vec![
-                ModelServiceTier::new(
-                    "priority",
-                    "Fast",
-                    "Route the request through Codex fast mode.",
-                )
-                .with_speed_tier("fast"),
-            ]),
+            presentation.clone(),
         )]
     }
 
@@ -289,6 +296,7 @@ async fn models_should_encode_provider_profiles_for_current_codex_clients() {
     assert_eq!(model["slug"], "grok-4.5");
     assert_eq!(model["default_reasoning_level"], "medium");
     assert_eq!(model["context_window"], 500_000);
+    assert_eq!(model["max_context_window"], 900_000);
     assert_eq!(model["apply_patch_tool_type"], "freeform");
     assert_eq!(model["additional_speed_tiers"], serde_json::json!(["fast"]));
     assert_eq!(
@@ -322,6 +330,34 @@ async fn models_should_encode_provider_profiles_for_current_codex_clients() {
     );
 }
 
+#[tokio::test]
+async fn models_should_preserve_unknown_context_windows() {
+    for (context_window, max_context_window) in
+        [(None, None), (Some(272_000), None), (None, Some(872_000))]
+    {
+        let presentation = ModelPresentation::default()
+            .with_context_window_tokens(context_window)
+            .with_max_context_window_tokens(max_context_window);
+        let response = api_router(ModelsExecution::with_presentation(presentation))
+            .await
+            .oneshot(authorized_request("/v1/models?client_version=0.145.0"))
+            .await
+            .expect("list Codex models response");
+        assert_eq!(response.status(), StatusCode::OK);
+        let body = to_bytes(response.into_body(), usize::MAX)
+            .await
+            .expect("read Codex models body");
+        let value: serde_json::Value = serde_json::from_slice(&body).expect("models JSON");
+        let model = &value["models"][0];
+
+        assert_eq!(model["context_window"], serde_json::json!(context_window));
+        assert_eq!(
+            model["max_context_window"],
+            serde_json::json!(max_context_window)
+        );
+    }
+}
+
 #[tokio::test]
 async fn models_should_keep_the_codex_contract_when_profiles_are_empty() {
     let response = api_router(ModelsExecution::new())
diff --git a/backend/crates/gateway-core/src/routing/mod.rs b/backend/crates/gateway-core/src/routing/mod.rs
index a55c341d1..ed57e0534 100644
--- a/backend/crates/gateway-core/src/routing/mod.rs
+++ b/backend/crates/gateway-core/src/routing/mod.rs
@@ -139,6 +139,7 @@ pub struct ModelPresentation {
     default_reasoning_effort: Option<String>,
     supported_reasoning_efforts: Vec<String>,
     context_window_tokens: Option<u64>,
+    max_context_window_tokens: Option<u64>,
     image_input: bool,
     agent_tools: bool,
     parallel_tool_calls: bool,
@@ -227,6 +228,16 @@ impl ModelPresentation {
         self
     }
 
+    /// 目录声明的可覆盖上限；客户端本地 context window 覆盖会被它钳制。
+    #[must_use]
+    pub const fn with_max_context_window_tokens(
+        mut self,
+        max_context_window_tokens: Option<u64>,
+    ) -> Self {
+        self.max_context_window_tokens = max_context_window_tokens;
+        self
+    }
+
     #[must_use]
     pub const fn with_image_input(mut self, image_input: bool) -> Self {
         self.image_input = image_input;
@@ -295,6 +306,11 @@ impl ModelPresentation {
         self.context_window_tokens
     }
 
+    #[must_use]
+    pub const fn max_context_window_tokens(&self) -> Option<u64> {
+        self.max_context_window_tokens
+    }
+
     #[must_use]
     pub const fn image_input(&self) -> bool {
         self.image_input
diff --git a/backend/crates/providers/openai/src/provider/observation.rs b/backend/crates/providers/openai/src/provider/observation.rs
index 1eff055f7..8f821107b 100644
--- a/backend/crates/providers/openai/src/provider/observation.rs
+++ b/backend/crates/providers/openai/src/provider/observation.rs
@@ -562,6 +562,12 @@ pub(super) fn codex_model_presentation(model: &CodexCatalogModel) -> ModelPresen
             .context_window_tokens()
             .map(std::num::NonZeroU64::get),
     )
+    .with_max_context_window_tokens(
+        model
+            .limits()
+            .max_context_window_tokens()
+            .map(std::num::NonZeroU64::get),
+    )
     .with_image_input(capabilities.image_input() == CodexCatalogCapabilityEvidence::DeclaredNative)
     // Codex Responses 工具协议随 API 支持一并可用；只有明确不支持才关闭。
     .with_agent_tools(
diff --git a/backend/crates/providers/openai/tests/provider/contract.rs b/backend/crates/providers/openai/tests/provider/contract.rs
index 783c72d8c..83fc0965f 100644
--- a/backend/crates/providers/openai/tests/provider/contract.rs
+++ b/backend/crates/providers/openai/tests/provider/contract.rs
@@ -6249,6 +6249,7 @@ async fn provider_compiles_catalog_presentation_for_codex_models() {
     assert_eq!(presentation.supported_reasoning_efforts(), ["low", "high"]);
     assert_eq!(presentation.default_reasoning_effort(), Some("low"));
     assert_eq!(presentation.context_window_tokens(), Some(272_000));
+    assert_eq!(presentation.max_context_window_tokens(), Some(272_000));
     assert!(presentation.image_input());
     assert!(presentation.agent_tools());
     assert!(presentation.parallel_tool_calls());
@@ -6258,6 +6259,48 @@ async fn provider_compiles_catalog_presentation_for_codex_models() {
     assert!(!presentation.hidden());
 }
 
+#[tokio::test]
+async fn provider_preserves_independent_catalog_context_windows() {
+    for (context_window, max_context_window) in [
+        (Some(272_000), Some(872_000)),
+        (Some(272_000), None),
+        (None, Some(872_000)),
+        (None, None),
+    ] {
+        let store = Arc::new(MemoryAccountStore::default());
+        create_account(&store, "acct_context_windows").await;
+        let server = MockServer::start().await;
+        let mut model = json!({"slug": "gpt-5.6-terra", "display_name": "GPT-5.6-Terra"});
+        if let Some(context_window) = context_window {
+            model["context_window"] = json!(context_window);
+        }
+        if let Some(max_context_window) = max_context_window {
+            model["max_context_window"] = json!(max_context_window);
+        }
+        Mock::given(method("GET"))
+            .and(path("/codex/models"))
+            .respond_with(ResponseTemplate::new(200).set_body_json(json!({"models": [model]})))
+            .expect(1)
+            .mount(&server)
+            .await;
+        let provider = provider_with_base_url(&store, server.uri());
+
+        let capabilities = provider
+            .query_model_capabilities()
+            .await
+            .expect("catalog model capabilities");
+        let presentation = capabilities[0].presentation().expect("model presentation");
+
+        assert_eq!(
+            (
+                presentation.context_window_tokens(),
+                presentation.max_context_window_tokens(),
+            ),
+            (context_window, max_context_window),
+        );
+    }
+}
+
 #[tokio::test]
 async fn provider_routes_catalog_model_when_supported_in_api_is_false() {
     let store = Arc::new(MemoryAccountStore::default());
diff --git a/backend/crates/providers/xai/src/provider/mod.rs b/backend/crates/providers/xai/src/provider/mod.rs
index feff8fbf1..241fd1511 100644
--- a/backend/crates/providers/xai/src/provider/mod.rs
+++ b/backend/crates/providers/xai/src/provider/mod.rs
@@ -563,6 +563,7 @@ fn default_grok_model_presentation() -> ModelPresentation {
         Some("xAI Grok 4.5 frontier model with reasoning and vision.".to_owned()),
     )
     .with_context_window_tokens(Some(500_000))
+    .with_max_context_window_tokens(Some(500_000))
     .with_image_input(true)
     .with_agent_tools(true, true)
 }
@@ -621,6 +622,8 @@ fn grok_model_presentation(model: &GrokCatalogModel) -> ModelPresentation {
     )
     .with_reasoning(default_reasoning, reasoning_efforts)
     .with_context_window_tokens(context_window_tokens)
+    // Grok 目录只声明一个窗口，继续将它作为客户端可覆盖上限。
+    .with_max_context_window_tokens(context_window_tokens)
     .with_image_input(known_grok_4_5)
     .with_agent_tools(
         tool_evidence != GrokCatalogCapabilityEvidence::DeclaredUnsupported,
diff --git a/backend/crates/providers/xai/tests/provider/contract.rs b/backend/crates/providers/xai/tests/provider/contract.rs
index 87d340dfa..1fbcb2e63 100644
--- a/backend/crates/providers/xai/tests/provider/contract.rs
+++ b/backend/crates/providers/xai/tests/provider/contract.rs
@@ -3183,6 +3183,7 @@ async fn provider_compiles_realtime_catalog_capabilities() {
         ["low", "medium", "high", "xhigh"]
     );
     assert_eq!(presentation.context_window_tokens(), Some(1_000_000));
+    assert_eq!(presentation.max_context_window_tokens(), Some(1_000_000));
     assert!(presentation.agent_tools());
 }
 
@@ -3209,6 +3210,7 @@ async fn provider_publishes_default_codex_profile_when_catalog_is_unavailable()
     assert_eq!(presentation.default_reasoning_effort(), None);
     assert!(presentation.supported_reasoning_efforts().is_empty());
     assert_eq!(presentation.context_window_tokens(), Some(500_000));
+    assert_eq!(presentation.max_context_window_tokens(), Some(500_000));
     assert!(presentation.agent_tools());
     assert!(presentation.parallel_tool_calls());
 }
diff --git a/docs/api.md b/docs/api.md
index 980426ab5..4f4e247b0 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -155,6 +155,11 @@ Responses WebSocket 仅接受文本 `response.create`，同一连接串行执行
 `GET /v1/models` 默认返回 OpenAI 兼容列表 `{"object": "list", "data": [...]}`；请求携带非空
 `client_version` query 参数（Codex 客户端）时改为返回 Codex 专用目录合同 `{"models": [...]}`。
 
+Codex 专用目录中的 `context_window` 与 `max_context_window` 分别表示默认上下文窗口和客户端本地
+覆盖的上限。OpenAI Provider 分别传递上游目录中的对应字段，缺失时保留 `null`；网关不通过部署配置
+覆盖这些值。Codex 客户端配置 `model_context_window` 后，按该值与非空 `max_context_window` 的较小值
+使用窗口；上限为空时保留客户端本地值。xAI 目录只声明一个窗口，其 Provider 继续以该值作为客户端覆盖上限。
+
 OpenAI 路径保留客户端 Responses wire 语义：请求 body 的未知字段和字段顺序保持不变（受控模型
 映射除外），HTTP SSE 与 WebSocket 的上游业务事件字节原样转发，response ID 按 opaque 值处理而不
 假设 UUID 或固定长度；OpenAI 上游错误 envelope 和允许下发的 opaque header 值也不由 canonical