diff --git a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
index f2a55aff69..0525c96a99 100644
--- a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
+++ b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json
@@ -10218,6 +10218,14 @@
               }
             ],
             "description": "Null if no requirements are configured (e.g. no requirements.toml/MDM entries)."
+          },
+          "supportsIndependentSpeedModes": {
+            "default": null,
+            "description": "Whether Fast and Ultra Fast requirements are enforced independently. Older servers omit this field and use Fast mode as a shared speed gate.",
+            "type": [
+              "boolean",
+              "null"
+            ]
           }
         },
         "title": "ConfigRequirementsReadResponse",
diff --git a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
index 926d0578df..6a6e3dad5d 100644
--- a/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
+++ b/codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json
@@ -6054,6 +6054,14 @@
             }
           ],
           "description": "Null if no requirements are configured (e.g. no requirements.toml/MDM entries)."
+        },
+        "supportsIndependentSpeedModes": {
+          "default": null,
+          "description": "Whether Fast and Ultra Fast requirements are enforced independently. Older servers omit this field and use Fast mode as a shared speed gate.",
+          "type": [
+            "boolean",
+            "null"
+          ]
         }
       },
       "title": "ConfigRequirementsReadResponse",
diff --git a/codex-rs/app-server-protocol/schema/json/v2/ConfigRequirementsReadResponse.json b/codex-rs/app-server-protocol/schema/json/v2/ConfigRequirementsReadResponse.json
index 8dbca4e59b..f2faa53496 100644
--- a/codex-rs/app-server-protocol/schema/json/v2/ConfigRequirementsReadResponse.json
+++ b/codex-rs/app-server-protocol/schema/json/v2/ConfigRequirementsReadResponse.json
@@ -1138,6 +1138,14 @@
         }
       ],
       "description": "Null if no requirements are configured (e.g. no requirements.toml/MDM entries)."
+    },
+    "supportsIndependentSpeedModes": {
+      "default": null,
+      "description": "Whether Fast and Ultra Fast requirements are enforced independently. Older servers omit this field and use Fast mode as a shared speed gate.",
+      "type": [
+        "boolean",
+        "null"
+      ]
     }
   },
   "title": "ConfigRequirementsReadResponse",
diff --git a/codex-rs/app-server-protocol/schema/precomputed/app-server-exports-experimental.json.zst b/codex-rs/app-server-protocol/schema/precomputed/app-server-exports-experimental.json.zst
index 4e3aa5a77f..aa9d93c0a8 100644
Binary files a/codex-rs/app-server-protocol/schema/precomputed/app-server-exports-experimental.json.zst and b/codex-rs/app-server-protocol/schema/precomputed/app-server-exports-experimental.json.zst differ
diff --git a/codex-rs/app-server-protocol/schema/precomputed/app-server-exports-stable.json.zst b/codex-rs/app-server-protocol/schema/precomputed/app-server-exports-stable.json.zst
index 3f816c600c..f64e9f9227 100644
Binary files a/codex-rs/app-server-protocol/schema/precomputed/app-server-exports-stable.json.zst and b/codex-rs/app-server-protocol/schema/precomputed/app-server-exports-stable.json.zst differ
diff --git a/codex-rs/app-server-protocol/schema/typescript/v2/ConfigRequirementsReadResponse.ts b/codex-rs/app-server-protocol/schema/typescript/v2/ConfigRequirementsReadResponse.ts
index f2de11d98e..0a452dd282 100644
--- a/codex-rs/app-server-protocol/schema/typescript/v2/ConfigRequirementsReadResponse.ts
+++ b/codex-rs/app-server-protocol/schema/typescript/v2/ConfigRequirementsReadResponse.ts
@@ -4,6 +4,11 @@
 import type { ConfigRequirements } from "./ConfigRequirements";
 
 export type ConfigRequirementsReadResponse = {
+/**
+ * Whether Fast and Ultra Fast requirements are enforced independently.
+ * Older servers omit this field and use Fast mode as a shared speed gate.
+ */
+supportsIndependentSpeedModes: boolean | null,
 /**
  * Null if no requirements are configured (e.g. no requirements.toml/MDM entries).
  */
diff --git a/codex-rs/app-server-protocol/src/protocol/v2/config.rs b/codex-rs/app-server-protocol/src/protocol/v2/config.rs
index 3689fffd92..2953911602 100644
--- a/codex-rs/app-server-protocol/src/protocol/v2/config.rs
+++ b/codex-rs/app-server-protocol/src/protocol/v2/config.rs
@@ -760,6 +760,10 @@ pub enum ResidencyRequirement {
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]
 pub struct ConfigRequirementsReadResponse {
+    /// Whether Fast and Ultra Fast requirements are enforced independently.
+    /// Older servers omit this field and use Fast mode as a shared speed gate.
+    #[serde(default)]
+    pub supports_independent_speed_modes: Option<bool>,
     /// Null if no requirements are configured (e.g. no requirements.toml/MDM entries).
     #[experimental(nested)]
     pub requirements: Option<ConfigRequirements>,
diff --git a/codex-rs/app-server/README.md b/codex-rs/app-server/README.md
index b4f29ab453..a40c0c9d25 100644
--- a/codex-rs/app-server/README.md
+++ b/codex-rs/app-server/README.md
@@ -211,6 +211,12 @@ Codex home must support compressed rollout files, including shared histories.
 
 ## Managed model provider requirements
 
+`configRequirements/read` reports `supportsIndependentSpeedModes: true` when
+`features.fast_mode` and `features.ultrafast_mode` independently control Fast and
+Ultra Fast. Older servers omit this field and use Fast mode as a shared speed
+gate. Missing individual feature requirements impose no additional restriction;
+the model catalog still determines which service tiers a model supports.
+
 Existing threads retain their provider configuration. Input RPCs reject requests when managed
 `model_provider` or `model_providers` requirements no longer match that configuration, or cannot
 be loaded. This covers turn start/steer, review, compaction, manual queue start, and active goal
diff --git a/codex-rs/app-server/src/request_processors/config_processor.rs b/codex-rs/app-server/src/request_processors/config_processor.rs
index e03f96685a..914abf4fd8 100644
--- a/codex-rs/app-server/src/request_processors/config_processor.rs
+++ b/codex-rs/app-server/src/request_processors/config_processor.rs
@@ -143,7 +143,10 @@ impl ConfigRequestProcessor {
             self.thread_manager.auth_manager().allowed_login_methods(),
         );
 
-        Ok(ConfigRequirementsReadResponse { requirements })
+        Ok(ConfigRequirementsReadResponse {
+            supports_independent_speed_modes: Some(true),
+            requirements,
+        })
     }
 
     pub(crate) async fn value_write(
diff --git a/codex-rs/app-server/tests/suite/v2/config_requirements_application.rs b/codex-rs/app-server/tests/suite/v2/config_requirements_application.rs
index 635bc2066b..ed4692bcc7 100644
--- a/codex-rs/app-server/tests/suite/v2/config_requirements_application.rs
+++ b/codex-rs/app-server/tests/suite/v2/config_requirements_application.rs
@@ -60,7 +60,7 @@ async fn application_network_defaults_and_null_base_url_are_exposed() -> Result<
     let mut server = start_server(&home).await?;
     assert_eq!(
         read_requirements(&mut server).await?,
-        json!({"requirements": null})
+        json!({"requirements": null, "supportsIndependentSpeedModes": true})
     );
     Ok(())
 }
diff --git a/codex-rs/app-server/tests/suite/v2/config_requirements_browser_use_tests.rs b/codex-rs/app-server/tests/suite/v2/config_requirements_browser_use_tests.rs
index a690d72ae9..6476079b65 100644
--- a/codex-rs/app-server/tests/suite/v2/config_requirements_browser_use_tests.rs
+++ b/codex-rs/app-server/tests/suite/v2/config_requirements_browser_use_tests.rs
@@ -66,7 +66,11 @@ async fn config_requirements_read_preserves_webmcp_policy() -> Result<()> {
                 "{contents}",
             );
         } else {
-            assert_eq!(wire, json!({ "requirements": null }), "{contents}");
+            assert_eq!(
+                wire,
+                json!({ "requirements": null, "supportsIndependentSpeedModes": true }),
+                "{contents}"
+            );
         }
     }
     Ok(())
diff --git a/codex-rs/app-server/tests/suite/v2/config_requirements_in_app_browser.rs b/codex-rs/app-server/tests/suite/v2/config_requirements_in_app_browser.rs
index 44f5d2fb35..76a80d2f07 100644
--- a/codex-rs/app-server/tests/suite/v2/config_requirements_in_app_browser.rs
+++ b/codex-rs/app-server/tests/suite/v2/config_requirements_in_app_browser.rs
@@ -63,7 +63,10 @@ async fn config_requirements_read_preserves_import_policy() -> Result<()> {
         if let Some(requirements) = wire["requirements"].as_object() {
             assert_eq!(requirements.get("inAppBrowser"), Some(&expected_wire));
         } else {
-            assert_eq!(wire, json!({ "requirements": null }));
+            assert_eq!(
+                wire,
+                json!({ "requirements": null, "supportsIndependentSpeedModes": true })
+            );
         }
         let response: ConfigRequirementsReadResponse = serde_json::from_value(wire)?;
         let actual = response
diff --git a/codex-rs/app-server/tests/suite/v2/config_requirements_login.rs b/codex-rs/app-server/tests/suite/v2/config_requirements_login.rs
index 679271935a..a3e2c487aa 100644
--- a/codex-rs/app-server/tests/suite/v2/config_requirements_login.rs
+++ b/codex-rs/app-server/tests/suite/v2/config_requirements_login.rs
@@ -47,7 +47,7 @@ async fn config_requirements_read_preserves_unrestricted_default(config: &str) -
     let (_home, mut server) = start_server(config, /*requirements*/ None).await?;
     assert_eq!(
         read_requirements(&mut server).await?,
-        json!({"requirements": null})
+        json!({"requirements": null, "supportsIndependentSpeedModes": true})
     );
     Ok(())
 }
diff --git a/codex-rs/app-server/tests/suite/v2/config_rpc.rs b/codex-rs/app-server/tests/suite/v2/config_rpc.rs
index 751324a173..c4ba5937d1 100644
--- a/codex-rs/app-server/tests/suite/v2/config_rpc.rs
+++ b/codex-rs/app-server/tests/suite/v2/config_rpc.rs
@@ -66,6 +66,46 @@ fn write_config(codex_home: &TempDir, contents: &str) -> Result<()> {
     )?)
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn config_requirements_read_exposes_independent_speed_policy() -> Result<()> {
+    for (fast_enabled, ultrafast_enabled) in
+        [(false, false), (false, true), (true, false), (true, true)]
+    {
+        let codex_home = TempDir::new()?;
+        std::fs::write(
+            codex_home.path().join("requirements.toml"),
+            format!(
+                "[features]\nfast_mode = {fast_enabled}\nultrafast_mode = {ultrafast_enabled}\n"
+            ),
+        )?;
+        let mut app_server = TestAppServer::builder()
+            .with_codex_home(codex_home.path())
+            .without_auto_env()
+            .build_initialized_with_timeout(DEFAULT_READ_TIMEOUT)
+            .await?;
+        let request_id = app_server.send_config_requirements_read_request().await?;
+        let response: ConfigRequirementsReadResponse =
+            timeout(DEFAULT_READ_TIMEOUT, app_server.read_response(request_id)).await??;
+        assert_eq!(
+            (
+                response.supports_independent_speed_modes,
+                response
+                    .requirements
+                    .expect("speed requirements")
+                    .feature_requirements
+            ),
+            (
+                Some(true),
+                Some(std::collections::BTreeMap::from([
+                    ("fast_mode".to_string(), fast_enabled),
+                    ("ultrafast_mode".to_string(), ultrafast_enabled),
+                ]))
+            ),
+        );
+    }
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn managed_auth_settings_are_exposed_enforced_and_read_only() -> Result<()> {
     let codex_home = TempDir::new()?;
diff --git a/codex-rs/app-server/tests/suite/v2/skills_list.rs b/codex-rs/app-server/tests/suite/v2/skills_list.rs
index 1b3d2948e0..a0a08c257c 100644
--- a/codex-rs/app-server/tests/suite/v2/skills_list.rs
+++ b/codex-rs/app-server/tests/suite/v2/skills_list.rs
@@ -713,7 +713,10 @@ async fn config_reads_complete_alongside_skills_list_request() -> Result<()> {
     assert!(config.layers.is_none());
     assert_eq!(
         requirements,
-        ConfigRequirementsReadResponse { requirements: None }
+        ConfigRequirementsReadResponse {
+            supports_independent_speed_modes: Some(true),
+            requirements: None,
+        }
     );
     assert!(!permission_profiles.data.is_empty());
 
diff --git a/codex-rs/config/src/cloud_config_bundle.rs b/codex-rs/config/src/cloud_config_bundle.rs
index 3a8898dd4f..62b65ecb20 100644
--- a/codex-rs/config/src/cloud_config_bundle.rs
+++ b/codex-rs/config/src/cloud_config_bundle.rs
@@ -62,6 +62,24 @@ impl CloudRequirementsTomlBundle {
             .into_iter()
             .rev()
             .map(|fragment| {
+                // Older backends used this fragment to deny every accelerated tier.
+                // Preserve that meaning through mixed deployments and rollbacks.
+                if fragment.id == "rbac-fast-mode"
+                    && let Ok(mut contents) = toml::from_str::<toml::Value>(&fragment.contents)
+                    && let Some(features) = contents
+                        .get_mut("features")
+                        .and_then(toml::Value::as_table_mut)
+                    && features.get("fast_mode").and_then(toml::Value::as_bool) == Some(false)
+                {
+                    features.insert("ultrafast_mode".to_string(), toml::Value::Boolean(false));
+                    return RequirementsLayerEntry::from_toml_value(
+                        RequirementSource::EnterpriseManaged {
+                            id: fragment.id,
+                            name: fragment.name,
+                        },
+                        contents,
+                    );
+                }
                 RequirementsLayerEntry::from_toml(
                     RequirementSource::EnterpriseManaged {
                         id: fragment.id,
diff --git a/codex-rs/config/src/cloud_config_bundle_tests.rs b/codex-rs/config/src/cloud_config_bundle_tests.rs
index 2871c2bfc3..7fafb64654 100644
--- a/codex-rs/config/src/cloud_config_bundle_tests.rs
+++ b/codex-rs/config/src/cloud_config_bundle_tests.rs
@@ -18,6 +18,77 @@ use std::sync::atomic::AtomicUsize;
 use std::sync::atomic::Ordering;
 use tempfile::tempdir;
 
+#[test]
+fn legacy_speed_denial_is_normalized_without_changing_other_fragments() {
+    for (id, contents, expected_ultrafast) in [
+        (
+            "rbac-fast-mode",
+            "[features]\nfast_mode = false",
+            Some(false),
+        ),
+        ("rbac-fast-mode", "[features]\nfast_mode = true", None),
+        ("admin-layer", "[features]\nfast_mode = false", None),
+    ] {
+        let requirements = compose_requirements(
+            CloudRequirementsTomlBundle {
+                enterprise_managed: vec![CloudRequirementsFragment {
+                    id: id.to_string(),
+                    name: id.to_string(),
+                    contents: contents.to_string(),
+                }],
+            }
+            .into_layers(),
+        )
+        .expect("valid cloud requirements")
+        .expect("requirements layer")
+        .into_toml();
+        assert_eq!(
+            requirements
+                .feature_requirements
+                .expect("feature requirements")
+                .entries
+                .get("ultrafast_mode")
+                .copied(),
+            expected_ultrafast,
+            "fragment={id}",
+        );
+    }
+}
+
+#[test]
+fn enterprise_speed_override_still_takes_precedence_over_legacy_baseline() {
+    let requirements = compose_requirements(
+        CloudRequirementsTomlBundle {
+            enterprise_managed: vec![
+                CloudRequirementsFragment {
+                    id: "admin-layer".to_string(),
+                    name: "Admin".to_string(),
+                    contents: "[features]\nultrafast_mode = true".to_string(),
+                },
+                CloudRequirementsFragment {
+                    id: "rbac-fast-mode".to_string(),
+                    name: "Legacy RBAC".to_string(),
+                    contents: "[features]\nfast_mode = false".to_string(),
+                },
+            ],
+        }
+        .into_layers(),
+    )
+    .expect("valid cloud requirements")
+    .expect("requirements layers")
+    .into_toml();
+    assert_eq!(
+        requirements
+            .feature_requirements
+            .expect("feature requirements")
+            .entries,
+        std::collections::BTreeMap::from([
+            ("fast_mode".to_string(), false),
+            ("ultrafast_mode".to_string(), true),
+        ]),
+    );
+}
+
 #[tokio::test]
 async fn shared_future_runs_once() {
     let counter = Arc::new(AtomicUsize::new(0));
diff --git a/codex-rs/core/config.schema.json b/codex-rs/core/config.schema.json
index 8931d9c789..f22c202af0 100644
--- a/codex-rs/core/config.schema.json
+++ b/codex-rs/core/config.schema.json
@@ -1205,6 +1205,9 @@
             "tui_app_server": {
               "type": "boolean"
             },
+            "ultrafast_mode": {
+              "type": "boolean"
+            },
             "unavailable_dummy_tools": {
               "type": "boolean"
             },
@@ -7381,6 +7384,9 @@
         "tui_app_server": {
           "type": "boolean"
         },
+        "ultrafast_mode": {
+          "type": "boolean"
+        },
         "unavailable_dummy_tools": {
           "type": "boolean"
         },
diff --git a/codex-rs/core/src/agent/role.rs b/codex-rs/core/src/agent/role.rs
index 494ec0d30c..cf43be3b40 100644
--- a/codex-rs/core/src/agent/role.rs
+++ b/codex-rs/core/src/agent/role.rs
@@ -206,6 +206,10 @@ mod role_overrides {
                     .enabled(Feature::FastMode)
                     .then(|| ServiceTier::Fast.request_value().to_string()),
                 Some(ServiceTier::Flex) => Some(ServiceTier::Flex.request_value().to_string()),
+                None if service_tier == "ultrafast" => next_config
+                    .features
+                    .enabled(Feature::UltrafastMode)
+                    .then(|| service_tier.clone()),
                 None => Some(service_tier.clone()),
             };
         }
diff --git a/codex-rs/core/src/config/mod.rs b/codex-rs/core/src/config/mod.rs
index edca5d2f2e..f00e09f612 100644
--- a/codex-rs/core/src/config/mod.rs
+++ b/codex-rs/core/src/config/mod.rs
@@ -3989,6 +3989,9 @@ impl Config {
                     .enabled(Feature::FastMode)
                     .then(|| ServiceTier::Fast.request_value().to_string()),
                 Some(ServiceTier::Flex) => Some(ServiceTier::Flex.request_value().to_string()),
+                None if service_tier == "ultrafast" => features
+                    .enabled(Feature::UltrafastMode)
+                    .then_some(service_tier),
                 None => Some(service_tier),
             }
         });
diff --git a/codex-rs/core/src/session/mod.rs b/codex-rs/core/src/session/mod.rs
index d343409813..427dfdcbd6 100644
--- a/codex-rs/core/src/session/mod.rs
+++ b/codex-rs/core/src/session/mod.rs
@@ -82,6 +82,7 @@ use codex_extension_api::PromptSlot;
 use codex_extension_api::TurnContextContributionInput;
 use codex_features::FEATURES;
 use codex_features::Feature;
+use codex_features::Features;
 use codex_features::unstable_features_warning_event;
 use codex_history::RolloutItem;
 use codex_hooks::Hooks;
@@ -834,14 +835,13 @@ impl Session {
                 /*developer_instructions*/ None,
             )
         });
-        let fast_mode_enabled = config.features.enabled(Feature::FastMode);
         let initial_service_tier_warning = unsupported_service_tier_warning(
             config.service_tier.as_deref(),
-            fast_mode_enabled,
+            &config.features,
             &model_info,
         );
         let service_tier =
-            get_service_tier(config.service_tier.clone(), fast_mode_enabled, &model_info);
+            get_service_tier(config.service_tier.clone(), &config.features, &model_info);
         let storage_originator = AuthStorageOriginator::from_client_name(&originator);
         let session_configuration = SessionConfiguration {
             turn_extension_init,
@@ -1124,14 +1124,14 @@ pub(crate) fn new_submission_id() -> String {
 
 pub(crate) fn get_service_tier(
     configured_service_tier: Option<String>,
-    fast_mode_enabled: bool,
+    features: &Features,
     model_info: &ModelInfo,
 ) -> Option<String> {
     let service_tier = configured_service_tier?;
     if service_tier == ServiceTier::Flex.request_value() {
         return Some(service_tier);
     }
-    if fast_mode_enabled
+    if features.service_tier_enabled(&service_tier)
         && (service_tier == SERVICE_TIER_DEFAULT_REQUEST_VALUE
             || model_info.supports_service_tier(&service_tier))
     {
@@ -1142,11 +1142,11 @@ pub(crate) fn get_service_tier(
 
 fn unsupported_service_tier_warning(
     configured_service_tier: Option<&str>,
-    fast_mode_enabled: bool,
+    features: &Features,
     model_info: &ModelInfo,
 ) -> Option<String> {
     let service_tier = configured_service_tier.filter(|service_tier| {
-        fast_mode_enabled
+        features.service_tier_enabled(service_tier)
             && *service_tier != SERVICE_TIER_DEFAULT_REQUEST_VALUE
             && !model_info.supports_service_tier(service_tier)
     })?;
@@ -3733,7 +3733,7 @@ impl Session {
                 let mut inherited_settings = ResolvedStepSettings::new(
                     Arc::new(selected),
                     Arc::clone(&settings.model_info),
-                    self.features.enabled(Feature::FastMode),
+                    &self.features,
                 );
                 inherited_settings.mcp_approvals_reviewer_override =
                     settings.mcp_approvals_reviewer_override;
diff --git a/codex-rs/core/src/session/reasoning_effort_tests.rs b/codex-rs/core/src/session/reasoning_effort_tests.rs
index d9ff4ba24e..2eb91a075c 100644
--- a/codex-rs/core/src/session/reasoning_effort_tests.rs
+++ b/codex-rs/core/src/session/reasoning_effort_tests.rs
@@ -40,7 +40,7 @@ async fn initial_replay_preserves_prewarmed_effort(history: InitialHistory) {
     let prewarm_settings = ResolvedStepSettings::new(
         Arc::new(selected.clone()),
         Arc::clone(&model_info),
-        /*fast_mode_enabled*/ false,
+        &codex_features::Features::default(),
     );
     // Force the ordering where prewarm pins its request before initial replay finishes.
     assert_eq!(
@@ -55,7 +55,7 @@ async fn initial_replay_preserves_prewarmed_effort(history: InitialHistory) {
     let turn_settings = ResolvedStepSettings::new(
         Arc::new(selected),
         model_info,
-        /*fast_mode_enabled*/ false,
+        &codex_features::Features::default(),
     );
     assert_eq!(
         session
diff --git a/codex-rs/core/src/session/review.rs b/codex-rs/core/src/session/review.rs
index d1080745c2..44ec95ff60 100644
--- a/codex-rs/core/src/session/review.rs
+++ b/codex-rs/core/src/session/review.rs
@@ -99,7 +99,7 @@ pub(super) async fn spawn_review_thread(
     let step_settings = Arc::new(ResolvedStepSettings::new(
         Arc::new(selected),
         Arc::new(model_info.clone()),
-        review_features.enabled(Feature::FastMode),
+        &review_features,
     ));
     per_turn_config.model = Some(model);
     per_turn_config.model_reasoning_effort = reasoning_effort;
diff --git a/codex-rs/core/src/session/startup_prewarm.rs b/codex-rs/core/src/session/startup_prewarm.rs
index b59308436d..e74e4668af 100644
--- a/codex-rs/core/src/session/startup_prewarm.rs
+++ b/codex-rs/core/src/session/startup_prewarm.rs
@@ -347,7 +347,7 @@ async fn schedule_startup_prewarm_inner(
     ) {
         crate::session::get_service_tier(
             session.services.agent_control.service_tier(),
-            session.features().enabled(Feature::FastMode),
+            &session.features(),
             &preconnect_model_info,
         )
     } else {
diff --git a/codex-rs/core/src/session/step_activation.rs b/codex-rs/core/src/session/step_activation.rs
index 8070b08ec6..6a972b8ba7 100644
--- a/codex-rs/core/src/session/step_activation.rs
+++ b/codex-rs/core/src/session/step_activation.rs
@@ -412,7 +412,7 @@ impl Session {
                 &constraints,
                 self.services.models_manager.as_ref(),
                 &overrides,
-                self.features.enabled(Feature::FastMode),
+                &self.features,
             )
             .await
             .map_err(|error| error.to_string())
diff --git a/codex-rs/core/src/session/step_activation_tests.rs b/codex-rs/core/src/session/step_activation_tests.rs
index 0202c02075..8d5647a4a7 100644
--- a/codex-rs/core/src/session/step_activation_tests.rs
+++ b/codex-rs/core/src/session/step_activation_tests.rs
@@ -1062,11 +1062,8 @@ async fn activation_must_match_the_retained_turn_authority(change: ManagedPolicy
     model_info.slug = "step-settings-policy-destination".to_string();
     let mut selected = current.selected().clone();
     selected.collaboration_mode.settings.model = model_info.slug.clone();
-    let destination = ResolvedStepSettings::new(
-        Arc::new(selected),
-        Arc::new(model_info),
-        session.features.enabled(Feature::FastMode),
-    );
+    let destination =
+        ResolvedStepSettings::new(Arc::new(selected), Arc::new(model_info), &session.features);
     let mut live = session.state.lock().await.session_configuration.clone();
     live.original_config_do_not_use = Arc::clone(&prepared.config);
     assert_eq!(
diff --git a/codex-rs/core/src/session/step_settings.rs b/codex-rs/core/src/session/step_settings.rs
index 701d480d4a..83b1edd04c 100644
--- a/codex-rs/core/src/session/step_settings.rs
+++ b/codex-rs/core/src/session/step_settings.rs
@@ -4,6 +4,7 @@ use crate::config::Constrained;
 use crate::config::ConstraintError;
 use crate::config::ConstraintResult;
 use codex_config::ConfigRequirements;
+use codex_features::Features;
 use codex_models_manager::ModelsManagerConfig;
 use codex_models_manager::manager::ModelsManager;
 use codex_otel::SessionTelemetry;
@@ -57,16 +58,13 @@ impl ResolvedStepSettings {
     pub(super) fn new(
         selected: Arc<StepSettings>,
         model_info: Arc<ModelInfo>,
-        fast_mode_enabled: bool,
+        features: &Features,
     ) -> Self {
         let reasoning_summary = selected
             .reasoning_summary
             .unwrap_or(model_info.default_reasoning_summary);
-        let service_tier = super::get_service_tier(
-            selected.service_tier.clone(),
-            fast_mode_enabled,
-            &model_info,
-        );
+        let service_tier =
+            super::get_service_tier(selected.service_tier.clone(), features, &model_info);
         Self {
             selected,
             model_info,
@@ -129,7 +127,7 @@ impl ResolvedStepSettings {
         constraints: &StepSettingsConstraints<'_>,
         models_manager: &dyn ModelsManager,
         overrides: &ModelInfoOverrides,
-        fast_mode_enabled: bool,
+        features: &Features,
     ) -> ConstraintResult<Self> {
         let selected = self.selected.apply(update, constraints)?;
         let model_info =
@@ -138,7 +136,7 @@ impl ResolvedStepSettings {
             } else {
                 Arc::new(selected.resolve_model_info(models_manager, overrides).await)
             };
-        let mut next = Self::new(Arc::new(selected), model_info, fast_mode_enabled);
+        let mut next = Self::new(Arc::new(selected), model_info, features);
         next.mcp_approvals_reviewer_override = update
             .approvals_reviewer
             .or(self.mcp_approvals_reviewer_override);
diff --git a/codex-rs/core/src/session/tests.rs b/codex-rs/core/src/session/tests.rs
index d5f52a97e2..a9bcb0477d 100644
--- a/codex-rs/core/src/session/tests.rs
+++ b/codex-rs/core/src/session/tests.rs
@@ -4703,7 +4703,7 @@ async fn turn_context_with_model_updates_model_fields() {
         *settings = ResolvedStepSettings::new(
             Arc::new(selected),
             Arc::clone(&settings.model_info),
-            /*fast_mode_enabled*/ true,
+            &codex_features::Features::with_defaults(),
         );
     });
     Arc::make_mut(&mut turn_context.config).service_tier =
@@ -4719,7 +4719,7 @@ async fn turn_context_with_model_updates_model_fields() {
     let current = Arc::new(ResolvedStepSettings::new(
         Arc::new(current_selection),
         Arc::clone(turn_context.model_info()),
-        /*fast_mode_enabled*/ true,
+        &codex_features::Features::with_defaults(),
     ));
     turn_context.next_step_settings.store(Arc::clone(&current));
     let updated = turn_context
@@ -4968,7 +4968,7 @@ fn get_service_tier_does_not_use_model_default_when_absent_and_fast_mode_enabled
     assert_eq!(
         get_service_tier(
             /*configured_service_tier*/ None,
-            /*fast_mode_enabled*/ true,
+            &codex_features::Features::with_defaults(),
             &model_info,
         ),
         None
@@ -4982,7 +4982,7 @@ fn get_service_tier_does_not_use_model_default_when_fast_mode_disabled() {
     assert_eq!(
         get_service_tier(
             /*configured_service_tier*/ None,
-            /*fast_mode_enabled*/ false,
+            &codex_features::Features::default(),
             &model_info,
         ),
         None
@@ -4996,7 +4996,7 @@ fn get_service_tier_keeps_supported_explicit_tier() {
     assert_eq!(
         get_service_tier(
             Some(ServiceTier::Fast.request_value().to_string()),
-            /*fast_mode_enabled*/ true,
+            &codex_features::Features::with_defaults(),
             &model_info,
         ),
         Some(ServiceTier::Fast.request_value().to_string())
@@ -5010,7 +5010,7 @@ fn get_service_tier_does_not_default_when_model_has_no_default() {
     assert_eq!(
         get_service_tier(
             /*configured_service_tier*/ None,
-            /*fast_mode_enabled*/ true,
+            &codex_features::Features::with_defaults(),
             &model_info,
         ),
         None
@@ -5024,7 +5024,7 @@ fn get_service_tier_drops_unsupported_configured_tier_when_fast_mode_enabled() {
     assert_eq!(
         get_service_tier(
             Some("unsupported".to_string()),
-            /*fast_mode_enabled*/ true,
+            &codex_features::Features::with_defaults(),
             &model_info,
         ),
         None
@@ -5032,7 +5032,7 @@ fn get_service_tier_drops_unsupported_configured_tier_when_fast_mode_enabled() {
     assert_eq!(
         get_service_tier(
             Some(SERVICE_TIER_DEFAULT_REQUEST_VALUE.to_string()),
-            /*fast_mode_enabled*/ true,
+            &codex_features::Features::with_defaults(),
             &model_info,
         ),
         Some(SERVICE_TIER_DEFAULT_REQUEST_VALUE.to_string())
@@ -5043,10 +5043,12 @@ fn get_service_tier_drops_unsupported_configured_tier_when_fast_mode_enabled() {
 fn get_service_tier_preserves_flex_without_catalog_support_or_fast_mode() {
     let model_info = model_with_default_service_tier(/*default_service_tier*/ None);
     for fast_mode_enabled in [false, true] {
+        let mut features = codex_features::Features::with_defaults();
+        features.set_enabled(Feature::FastMode, fast_mode_enabled);
         assert_eq!(
             get_service_tier(
                 Some(ServiceTier::Flex.request_value().to_string()),
-                fast_mode_enabled,
+                &features,
                 &model_info,
             ),
             Some(ServiceTier::Flex.request_value().to_string())
@@ -5061,7 +5063,7 @@ fn get_service_tier_ignores_non_flex_tiers_when_fast_mode_disabled() {
     assert_eq!(
         get_service_tier(
             Some(ServiceTier::Fast.request_value().to_string()),
-            /*fast_mode_enabled*/ false,
+            &codex_features::Features::default(),
             &model_info,
         ),
         None
@@ -5069,7 +5071,7 @@ fn get_service_tier_ignores_non_flex_tiers_when_fast_mode_disabled() {
     assert_eq!(
         get_service_tier(
             Some(SERVICE_TIER_DEFAULT_REQUEST_VALUE.to_string()),
-            /*fast_mode_enabled*/ false,
+            &codex_features::Features::default(),
             &model_info,
         ),
         None
@@ -5077,7 +5079,7 @@ fn get_service_tier_ignores_non_flex_tiers_when_fast_mode_disabled() {
     assert_eq!(
         get_service_tier(
             Some("unsupported".to_string()),
-            /*fast_mode_enabled*/ false,
+            &codex_features::Features::default(),
             &model_info,
         ),
         None
@@ -5085,7 +5087,7 @@ fn get_service_tier_ignores_non_flex_tiers_when_fast_mode_disabled() {
     assert_eq!(
         get_service_tier(
             /*configured_service_tier*/ None,
-            /*fast_mode_enabled*/ false,
+            &codex_features::Features::default(),
             &model_info,
         ),
         None
@@ -7036,7 +7038,7 @@ pub(crate) async fn make_session_and_context() -> (Session, TurnContext) {
         Arc::new(super::step_settings::ResolvedStepSettings::new(
             Arc::clone(&session_configuration.step_settings),
             Arc::new(model_info),
-            config.features.enabled(Feature::FastMode),
+            &config.features,
         )),
         &models_manager,
         /*network*/ None,
@@ -9302,7 +9304,7 @@ where
         Arc::new(super::step_settings::ResolvedStepSettings::new(
             Arc::clone(&session_configuration.step_settings),
             Arc::new(model_info),
-            config.features.enabled(Feature::FastMode),
+            &config.features,
         )),
         &models_manager,
         /*network*/ None,
@@ -11326,7 +11328,7 @@ async fn build_initial_context_uses_retained_step_after_model_change() {
         .store(Arc::new(ResolvedStepSettings::new(
             Arc::new(selected_b),
             Arc::new(model_b),
-            /*fast_mode_enabled*/ false,
+            &codex_features::Features::default(),
         )));
     let step_b = session
         .capture_step_context(Arc::clone(&turn_context), &CancellationToken::new())
diff --git a/codex-rs/core/src/session/turn_context.rs b/codex-rs/core/src/session/turn_context.rs
index e8f9abb256..d58b7cd888 100644
--- a/codex-rs/core/src/session/turn_context.rs
+++ b/codex-rs/core/src/session/turn_context.rs
@@ -822,7 +822,7 @@ impl TurnContext {
         let step_settings = Arc::new(ResolvedStepSettings::new(
             Arc::new(selected),
             model_info,
-            config.features.enabled(Feature::FastMode),
+            &config.features,
         ));
         config.service_tier = step_settings.service_tier.clone();
         let session_telemetry = step_settings.telemetry(&self.session_telemetry);
@@ -1395,7 +1395,7 @@ impl Session {
         let step_settings = Arc::new(ResolvedStepSettings::new(
             Arc::clone(&session_configuration.step_settings),
             Arc::new(model_info),
-            self.features.enabled(Feature::FastMode),
+            &self.features,
         ));
         let mut turn_context: TurnContext = Self::make_turn_context(
             self.thread_id(),
diff --git a/codex-rs/core/tests/suite/agent_websocket.rs b/codex-rs/core/tests/suite/agent_websocket.rs
index 2262343cf1..28d0554e54 100644
--- a/codex-rs/core/tests/suite/agent_websocket.rs
+++ b/codex-rs/core/tests/suite/agent_websocket.rs
@@ -27,11 +27,15 @@ use std::time::Duration;
 
 const WS_V2_BETA_HEADER_VALUE: &str = "responses_websockets=2026-02-06";
 
-#[test_case::test_case(true; "fast mode enabled")]
-#[test_case::test_case(false; "fast mode disabled")]
+#[test_case::test_case("priority", true, false; "fast mode enabled")]
+#[test_case::test_case("priority", false, true; "fast mode disabled")]
+#[test_case::test_case("ultrafast", false, true; "ultrafast mode enabled")]
+#[test_case::test_case("ultrafast", true, false; "ultrafast mode disabled")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn spawned_agent_prewarm_handshake_inherits_effective_root_service_tier(
+    tier: &'static str,
     fast_mode_enabled: bool,
+    ultrafast_mode_enabled: bool,
 ) -> Result<()> {
     skip_if_no_network!(Ok(()));
 
@@ -63,7 +67,11 @@ async fn spawned_agent_prewarm_handshake_inherits_effective_root_service_tier(
         ],
     ])
     .await;
-    let tier = ServiceTier::Fast.request_value();
+    let tier_enabled = if tier == "ultrafast" {
+        ultrafast_mode_enabled
+    } else {
+        fast_mode_enabled
+    };
     let test = test_codex()
         .with_model("gpt-5.4")
         .with_auth(CodexAuth::create_dummy_chatgpt_auth_for_testing())
@@ -89,7 +97,11 @@ async fn spawned_agent_prewarm_handshake_inherits_effective_root_service_tier(
                     .disable(Feature::FastMode)
                     .expect("fast mode");
             }
-            config.service_tier = Some(ServiceTier::Fast.request_value().to_string());
+            config
+                .features
+                .set_enabled(Feature::UltrafastMode, ultrafast_mode_enabled)
+                .expect("configure Ultra Fast mode");
+            config.service_tier = Some(tier.to_string());
         })
         .build_with_websocket_server(&server)
         .await?;
@@ -122,7 +134,7 @@ async fn spawned_agent_prewarm_handshake_inherits_effective_root_service_tier(
         "child startup should connect before its first turn"
     );
     let handshakes = server.handshakes();
-    let expected_hint = if fast_mode_enabled {
+    let expected_hint = if tier_enabled {
         format!("model=gpt-5.4;tier={tier}")
     } else {
         "model=gpt-5.4".to_string()
@@ -140,7 +152,7 @@ async fn spawned_agent_prewarm_handshake_inherits_effective_root_service_tier(
     assert_eq!(child_warmup["generate"], false);
     assert_eq!(
         child_warmup["service_tier"].as_str(),
-        fast_mode_enabled.then_some(tier)
+        tier_enabled.then_some(tier)
     );
     assert_eq!(server.handshakes().len(), 2);
     child.shutdown_and_wait().await?;
diff --git a/codex-rs/core/tests/suite/client.rs b/codex-rs/core/tests/suite/client.rs
index c232097e72..4f45445509 100644
--- a/codex-rs/core/tests/suite/client.rs
+++ b/codex-rs/core/tests/suite/client.rs
@@ -107,6 +107,63 @@ const INSTALLATION_ID_FILENAME: &str = "installation_id";
 const TEST_WINDOW_ID: &str = "test-thread:0";
 const TEST_INSTALLATION_ID: &str = "11111111-1111-4111-8111-111111111111";
 
+#[test_case::test_case(false, false)]
+#[test_case::test_case(false, true)]
+#[test_case::test_case(true, false)]
+#[test_case::test_case(true, true)]
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn responses_request_enforces_independent_speed_requirements(
+    fast_enabled: bool,
+    ultrafast_enabled: bool,
+) -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+    for (tier, enabled) in [("priority", fast_enabled), ("ultrafast", ultrafast_enabled)] {
+        for configure_at_start in [false, true] {
+            let server = start_mock_server().await;
+            let response_mock = mount_sse_once(&server, sse(vec![ev_completed("done")])).await;
+            let test = test_codex()
+                .with_model("gpt-5.4")
+                .with_model_info_override("gpt-5.4", move |model| {
+                    model.service_tiers = vec![codex_protocol::openai_models::ModelServiceTier {
+                        id: tier.to_string(),
+                        name: tier.to_string(),
+                        description: String::new(),
+                    }];
+                })
+                .with_config(move |config| {
+                    config
+                        .features
+                        .set_enabled(Feature::FastMode, fast_enabled)
+                        .expect("configure Fast mode");
+                    config
+                        .features
+                        .set_enabled(Feature::UltrafastMode, ultrafast_enabled)
+                        .expect("configure Ultra Fast mode");
+                    config.service_tier = configure_at_start.then(|| tier.to_string());
+                })
+                .build_with_auto_env(&server)
+                .await?;
+            if !configure_at_start {
+                core_test_support::submit_thread_settings(
+                    &test.codex,
+                    ThreadSettingsOverrides {
+                        service_tier: Some(Some(tier.to_string())),
+                        ..Default::default()
+                    },
+                )
+                .await?;
+            }
+            test.submit_turn("hello").await?;
+            assert_eq!(
+                response_mock.single_request().body_json()["service_tier"].as_str(),
+                enabled.then_some(tier),
+                "tier={tier}, configure_at_start={configure_at_start}",
+            );
+        }
+    }
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn responses_request_preserves_flex_without_catalog_support_or_fast_mode()
 -> anyhow::Result<()> {
diff --git a/codex-rs/features/src/lib.rs b/codex-rs/features/src/lib.rs
index 5d3804662f..44d86eb43f 100644
--- a/codex-rs/features/src/lib.rs
+++ b/codex-rs/features/src/lib.rs
@@ -401,6 +401,8 @@ pub enum Feature {
     Artifact,
     /// Enable Fast mode selection in the TUI and request layer.
     FastMode,
+    /// Enable Ultra Fast mode independently of Fast mode.
+    UltrafastMode,
     /// Enable explicitly requested model changes for later step captures.
     StepModelSwitching,
     /// Enable voice conversations in the TUI.
@@ -552,6 +554,15 @@ impl Features {
         self.enabled.contains(&f)
     }
 
+    /// Whether a routing tier is enabled, independently of model catalog support.
+    pub fn service_tier_enabled(&self, service_tier: &str) -> bool {
+        match service_tier {
+            "flex" => true,
+            "ultrafast" => self.enabled(Feature::UltrafastMode),
+            _ => self.enabled(Feature::FastMode),
+        }
+    }
+
     /// Returns whether persistent execution is enabled for the selected effort.
     pub fn persistent_execution_enabled(&self, reasoning_effort: Option<&ReasoningEffort>) -> bool {
         reasoning_effort == Some(&ReasoningEffort::Persistent)
@@ -1892,6 +1903,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::Stable,
         default_enabled: true,
     },
+    FeatureSpec {
+        id: Feature::UltrafastMode,
+        key: "ultrafast_mode",
+        stage: Stage::Stable,
+        default_enabled: true,
+    },
     FeatureSpec {
         id: Feature::StepModelSwitching,
         key: "step_model_switching",
diff --git a/codex-rs/tui/src/app/agents_overview.rs b/codex-rs/tui/src/app/agents_overview.rs
index 07f56a1275..d069a6c129 100644
--- a/codex-rs/tui/src/app/agents_overview.rs
+++ b/codex-rs/tui/src/app/agents_overview.rs
@@ -1081,7 +1081,8 @@ impl App {
         );
         if server_model_cleared
             && config.model.is_none()
-            && config.features.enabled(Feature::FastMode)
+            && (config.features.enabled(Feature::FastMode)
+                || config.features.enabled(Feature::UltrafastMode))
         {
             // Bootstrap's fallback model may be seeded from the client. Resolve tiers
             // against the server catalog when config/read cleared the model.
diff --git a/codex-rs/tui/src/app/tests/luna_reserve_recovery_tests.rs b/codex-rs/tui/src/app/tests/luna_reserve_recovery_tests.rs
index f56c31af5c..8dbceb0cda 100644
--- a/codex-rs/tui/src/app/tests/luna_reserve_recovery_tests.rs
+++ b/codex-rs/tui/src/app/tests/luna_reserve_recovery_tests.rs
@@ -188,6 +188,8 @@ async fn luna_reserve_recovery_restores_task_and_pending_turn_after_fresh_backen
         configure_reserve_catalog(&mut app);
         app.chat_widget
             .set_feature_enabled(Feature::FastMode, /*enabled*/ false);
+        app.chat_widget
+            .set_feature_enabled(Feature::UltrafastMode, /*enabled*/ false);
         app.chat_widget
             .set_reasoning_effort(Some(ReasoningEffortConfig::High));
         let original_mode = app.chat_widget.effective_collaboration_mode();
diff --git a/codex-rs/tui/src/app_server_session.rs b/codex-rs/tui/src/app_server_session.rs
index 25a1d20a54..475b8a0773 100644
--- a/codex-rs/tui/src/app_server_session.rs
+++ b/codex-rs/tui/src/app_server_session.rs
@@ -718,15 +718,19 @@ impl AppServerSession {
             },
             async { Ok(crate::collaboration_modes::list(self.request_handle()).await) },
         )?;
-        self.managed_new_thread_defaults = requirements
-            .requirements
-            .and_then(|requirements| requirements.models)
-            .and_then(|models| models.new_thread);
-        let available_models = models
+        let mut available_models = models
             .data
             .into_iter()
             .map(model_preset_from_api_model)
             .collect::<Vec<_>>();
+        crate::service_tier_resolution::constrain_server_service_tiers(
+            &mut available_models,
+            &requirements,
+        );
+        self.managed_new_thread_defaults = requirements
+            .requirements
+            .and_then(|requirements| requirements.models)
+            .and_then(|models| models.new_thread);
         let default_model = config
             .model
             .clone()
diff --git a/codex-rs/tui/src/chatwidget/service_tiers.rs b/codex-rs/tui/src/chatwidget/service_tiers.rs
index ad48da4495..6ff2786510 100644
--- a/codex-rs/tui/src/chatwidget/service_tiers.rs
+++ b/codex-rs/tui/src/chatwidget/service_tiers.rs
@@ -66,10 +66,10 @@ impl ChatWidget {
     }
 
     pub(super) fn sync_service_tier_commands(&mut self) {
+        let commands = self.current_model_service_tier_commands();
         self.bottom_pane
-            .set_service_tier_commands_enabled(self.fast_mode_enabled());
-        self.bottom_pane
-            .set_service_tier_commands(self.current_model_service_tier_commands());
+            .set_service_tier_commands_enabled(!commands.is_empty());
+        self.bottom_pane.set_service_tier_commands(commands);
     }
 
     pub(super) fn current_model_service_tier_commands(&self) -> Vec<ServiceTierCommand> {
@@ -85,6 +85,7 @@ impl ChatWidget {
                         preset
                             .service_tiers
                             .into_iter()
+                            .filter(|tier| self.config.features.service_tier_enabled(&tier.id))
                             .map(|tier| ServiceTierCommand {
                                 id: tier.id,
                                 name: tier.name.to_lowercase(),
diff --git a/codex-rs/tui/src/chatwidget/settings.rs b/codex-rs/tui/src/chatwidget/settings.rs
index c85b798769..a5ddae2160 100644
--- a/codex-rs/tui/src/chatwidget/settings.rs
+++ b/codex-rs/tui/src/chatwidget/settings.rs
@@ -116,7 +116,7 @@ impl ChatWidget {
             self.set_daybreak_enabled(self.daybreak_enabled);
             self.refresh_status_surfaces();
         }
-        if feature == Feature::FastMode {
+        if matches!(feature, Feature::FastMode | Feature::UltrafastMode) {
             self.refresh_effective_service_tier();
             self.sync_service_tier_commands();
         }
diff --git a/codex-rs/tui/src/chatwidget/slash_dispatch.rs b/codex-rs/tui/src/chatwidget/slash_dispatch.rs
index d45776cbb9..182a696b24 100644
--- a/codex-rs/tui/src/chatwidget/slash_dispatch.rs
+++ b/codex-rs/tui/src/chatwidget/slash_dispatch.rs
@@ -1241,7 +1241,7 @@ impl ChatWidget {
             plugins_command_enabled: self.config.features.enabled(Feature::Plugins),
             token_activity_command_enabled: self.has_codex_backend_auth,
             goal_command_enabled: self.config.features.enabled(Feature::Goals),
-            service_tier_commands_enabled: self.fast_mode_enabled(),
+            service_tier_commands_enabled: !self.current_model_service_tier_commands().is_empty(),
             daybreak_command_description: self.daybreak_command_description(),
             voice_command_enabled: self.realtime_conversation_available_for_thread,
             worktrees_enabled: self.config.features.enabled(Feature::Worktrees)
diff --git a/codex-rs/tui/src/chatwidget/tests/slash_commands.rs b/codex-rs/tui/src/chatwidget/tests/slash_commands.rs
index 439a368784..3589c3df26 100644
--- a/codex-rs/tui/src/chatwidget/tests/slash_commands.rs
+++ b/codex-rs/tui/src/chatwidget/tests/slash_commands.rs
@@ -106,6 +106,56 @@ fn next_copy_selection(
     selection
 }
 
+#[tokio::test]
+async fn service_tier_commands_and_saved_selection_respect_independent_speed_policy() {
+    for (fast_enabled, ultrafast_enabled) in [(false, true), (true, false)] {
+        let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.5")).await;
+        let mut preset = get_available_model(&chat, "gpt-5.5");
+        preset.service_tiers = ["priority", "ultrafast"]
+            .into_iter()
+            .map(|tier| codex_protocol::openai_models::ModelServiceTier {
+                id: tier.to_string(),
+                name: tier.to_string(),
+                description: format!("{tier} processing"),
+            })
+            .collect();
+        preset.default_service_tier = Some("ultrafast".to_string());
+        chat.model_catalog = std::sync::Arc::new(ModelCatalog::new(vec![preset]));
+        chat.set_feature_enabled(Feature::FastMode, fast_enabled);
+        chat.set_feature_enabled(Feature::UltrafastMode, ultrafast_enabled);
+        chat.set_service_tier(Some("ultrafast".to_string()));
+        assert_eq!(
+            chat.current_service_tier(),
+            ultrafast_enabled.then_some("ultrafast")
+        );
+        assert_eq!(
+            chat.current_model_service_tier_commands()
+                .into_iter()
+                .map(|tier| tier.id)
+                .collect::<Vec<_>>(),
+            vec![
+                if ultrafast_enabled {
+                    "ultrafast"
+                } else {
+                    "priority"
+                }
+                .to_string()
+            ],
+        );
+        chat.bottom_pane
+            .set_composer_text("/ultra".to_string(), Vec::new(), Vec::new());
+        let snapshot_name = if ultrafast_enabled {
+            "ultrafast_command_allowed"
+        } else {
+            "ultrafast_command_denied"
+        };
+        insta::assert_snapshot!(
+            snapshot_name,
+            normalize_snapshot_paths(render_bottom_popup(&chat, /*width*/ 80))
+        );
+    }
+}
+
 #[tokio::test]
 async fn service_tier_commands_lowercase_catalog_names() {
     let (mut chat, _rx, _op_rx) = make_chatwidget_manual(Some("gpt-5.5")).await;
diff --git a/codex-rs/tui/src/chatwidget/tests/snapshots/codex_tui__chatwidget__tests__slash_commands__ultrafast_command_allowed.snap b/codex-rs/tui/src/chatwidget/tests/snapshots/codex_tui__chatwidget__tests__slash_commands__ultrafast_command_allowed.snap
new file mode 100644
index 0000000000..6505ef3a24
--- /dev/null
+++ b/codex-rs/tui/src/chatwidget/tests/snapshots/codex_tui__chatwidget__tests__slash_commands__ultrafast_command_allowed.snap
@@ -0,0 +1,9 @@
+---
+source: tui/src/chatwidget/tests/slash_commands.rs
+expression: "render_bottom_popup(&chat, 80)"
+---
+› /ultrafast  ultrafast processing
+
+› /ultra
+
+  GPT-5.5 default · /tmp/project
diff --git a/codex-rs/tui/src/chatwidget/tests/snapshots/codex_tui__chatwidget__tests__slash_commands__ultrafast_command_denied.snap b/codex-rs/tui/src/chatwidget/tests/snapshots/codex_tui__chatwidget__tests__slash_commands__ultrafast_command_denied.snap
new file mode 100644
index 0000000000..25210e0ac9
--- /dev/null
+++ b/codex-rs/tui/src/chatwidget/tests/snapshots/codex_tui__chatwidget__tests__slash_commands__ultrafast_command_denied.snap
@@ -0,0 +1,7 @@
+---
+source: tui/src/chatwidget/tests/slash_commands.rs
+expression: "render_bottom_popup(&chat, 80)"
+---
+› /ultra
+
+  GPT-5.5 default · /tmp/project
diff --git a/codex-rs/tui/src/service_tier_resolution.rs b/codex-rs/tui/src/service_tier_resolution.rs
index 47f017cb38..223d615d7a 100644
--- a/codex-rs/tui/src/service_tier_resolution.rs
+++ b/codex-rs/tui/src/service_tier_resolution.rs
@@ -4,6 +4,38 @@ use codex_protocol::config_types::SERVICE_TIER_DEFAULT_REQUEST_VALUE;
 use codex_protocol::config_types::ServiceTier;
 use codex_protocol::openai_models::ModelPreset;
 
+pub(crate) fn constrain_server_service_tiers(
+    models: &mut [ModelPreset],
+    requirements: &codex_app_server_protocol::ConfigRequirementsReadResponse,
+) {
+    let Some(features) = requirements
+        .requirements
+        .as_ref()
+        .and_then(|requirements| requirements.feature_requirements.as_ref())
+    else {
+        return;
+    };
+    let fast_enabled = features.get("fast_mode") != Some(&false);
+    // Older servers enforce Ultra Fast through their shared Fast mode gate.
+    let ultrafast_enabled = features.get("ultrafast_mode") != Some(&false)
+        && (requirements.supports_independent_speed_modes == Some(true) || fast_enabled);
+    let tier_enabled = |tier: &str| match tier {
+        "flex" => true,
+        "ultrafast" => ultrafast_enabled,
+        _ => fast_enabled,
+    };
+    for model in models {
+        model.service_tiers.retain(|tier| tier_enabled(&tier.id));
+        if model
+            .default_service_tier
+            .as_deref()
+            .is_some_and(|tier| !tier_enabled(tier))
+        {
+            model.default_service_tier = None;
+        }
+    }
+}
+
 pub(crate) fn configured_service_tier(
     config: &Config,
     notices: &codex_config::types::Notice,
@@ -24,12 +56,8 @@ pub(crate) fn effective_service_tier(
     if configured.as_deref() == Some(ServiceTier::Flex.request_value()) {
         return configured;
     }
-    if !config.features.enabled(Feature::FastMode) {
-        return None;
-    }
-
     let Some(preset) = models.iter().find(|preset| preset.model == model) else {
-        return configured;
+        return configured.filter(|tier| config.features.service_tier_enabled(tier));
     };
 
     match configured.as_deref() {
@@ -41,6 +69,7 @@ pub(crate) fn effective_service_tier(
             .clone()
             .filter(|service_tier| model_supports_service_tier(preset, service_tier)),
     }
+    .filter(|tier| config.features.service_tier_enabled(tier))
 }
 
 pub(crate) fn service_tier_update_for_core(
@@ -54,7 +83,9 @@ pub(crate) fn service_tier_update_for_core(
         return Some(Some(service_tier));
     }
 
-    if !config.features.enabled(Feature::FastMode) {
+    if !config.features.enabled(Feature::FastMode)
+        && !config.features.enabled(Feature::UltrafastMode)
+    {
         return None;
     }
 
diff --git a/sdk/python/src/openai_codex/generated/v2_all.py b/sdk/python/src/openai_codex/generated/v2_all.py
index 58f45ffcf2..4a5cd1f191 100644
--- a/sdk/python/src/openai_codex/generated/v2_all.py
+++ b/sdk/python/src/openai_codex/generated/v2_all.py
@@ -11840,6 +11840,13 @@ class ConfigRequirementsReadResponse(BaseModel):
             description="Null if no requirements are configured (e.g. no requirements.toml/MDM entries)."
         ),
     ] = None
+    supports_independent_speed_modes: Annotated[
+        bool | None,
+        Field(
+            alias="supportsIndependentSpeedModes",
+            description="Whether Fast and Ultra Fast requirements are enforced independently. Older servers omit this field and use Fast mode as a shared speed gate.",
+        ),
+    ] = None
 
 
 class ExternalAgentConfigDetectResponse(BaseModel):