feature: add Codex Fast Mode support

apps/code/src/main/services/agent/schemas.ts

@@ -35,6 +35,7 @@ export const sessionConfigSchema = z.object({
 export type SessionConfig = z.infer<typeof sessionConfigSchema>;
 
 // Start session input/output
+const codexServiceTierSchema = z.enum(["standard", "fast", "flex"]);
 
 export const startSessionInput = z.object({
   taskId: z.string(),
@@ -50,6 +51,7 @@ export const startSessionInput = z.object({
   customInstructions: z.string().max(2000).optional(),
   effort: effortLevelSchema.optional(),
   model: z.string().optional(),
+  serviceTier: codexServiceTierSchema.optional(),
   jsonSchema: z.record(z.string(), z.unknown()).nullish(),
 });
 
@@ -174,6 +176,7 @@ export const reconnectSessionInput = z.object({
   permissionMode: z.string().optional(),
   customInstructions: z.string().max(2000).optional(),
   effort: effortLevelSchema.optional(),
+  serviceTier: codexServiceTierSchema.optional(),
   jsonSchema: z.record(z.string(), z.unknown()).nullish(),
 });
 

apps/code/src/main/services/agent/service.ts

@@ -224,6 +224,8 @@ interface SessionConfig {
   effort?: EffortLevel;
   /** Model to use for the session (e.g. "claude-sonnet-4-6") */
   model?: string;
+  /** Codex service tier, e.g. "standard" or "fast" */
+  serviceTier?: string;
   /** JSON Schema for structured task output — when set, the agent gets a create_output tool */
   jsonSchema?: Record<string, unknown> | null;
 }
@@ -536,6 +538,7 @@ When creating pull requests, add the following footer at the end of the PR descr
       customInstructions,
       effort,
       model,
+      serviceTier,
       jsonSchema,
     } = config;
 
@@ -599,6 +602,7 @@ When creating pull requests, add the following footer at the end of the PR descr
         codexBinaryPath:
           adapter === "codex" ? this.getCodexBinaryPath() : undefined,
         model,
+        serviceTier,
         instructions: adapter === "codex" ? systemPrompt.append : undefined,
         onStructuredOutput: jsonSchema
           ? async (output) => {
@@ -1502,6 +1506,7 @@ For git operations while detached:
         "customInstructions" in params ? params.customInstructions : undefined,
       effort: "effort" in params ? params.effort : undefined,
       model: "model" in params ? params.model : undefined,
+      serviceTier: "serviceTier" in params ? params.serviceTier : undefined,
       jsonSchema: "jsonSchema" in params ? params.jsonSchema : undefined,
     };
   }
@@ -1767,10 +1772,38 @@ For git operations while detached:
         currentValue: resolvedModelId,
         options: modelOptions,
         category: "model",
-        description: "Choose which model Claude should use",
+        description: `Choose which model ${adapter === "codex" ? "Codex" : "Claude"} should use`,
       },
     ];
 
+    if (adapter === "codex") {
+      configOptions.push({
+        id: "service_tier",
+        name: "Speed",
+        type: "select",
+        currentValue: "standard",
+        options: [
+          {
+            value: "standard",
+            name: "Standard",
+            description: "Default Codex service tier",
+          },
+          {
+            value: "fast",
+            name: "Fast",
+            description: "Request Codex fast mode for lower latency",
+          },
+          {
+            value: "flex",
+            name: "Flex",
+            description: "Request Codex flex mode",
+          },
+        ],
+        category: "service_tier",
+        description: "Choose the Codex service tier for new turns",
+      });
+    }
+
     const effortOpts = getReasoningEffortOptions(adapter, resolvedModelId);
     if (effortOpts) {
       configOptions.push({

apps/code/src/renderer/api/posthogClient.test.ts

@@ -25,6 +25,7 @@ describe("PostHogAPIClient", () => {
       adapter: "codex",
       model: "gpt-5.4",
       reasoningLevel: "high",
+      serviceTier: "fast",
     });
 
     expect(post).toHaveBeenCalledWith(
@@ -37,6 +38,7 @@ describe("PostHogAPIClient", () => {
           runtime_adapter: "codex",
           model: "gpt-5.4",
           reasoning_effort: "high",
+          service_tier: "fast",
         }),
       }),
     );
@@ -154,6 +156,7 @@ describe("PostHogAPIClient", () => {
         adapter: "codex",
         model: "gpt-5.4",
         reasoningLevel: "high",
+        serviceTier: "fast",
         initialPermissionMode: "auto",
       }),
     ).resolves.toEqual({ id: "run-123", environment: "cloud" });
@@ -169,6 +172,7 @@ describe("PostHogAPIClient", () => {
             runtime_adapter: "codex",
             model: "gpt-5.4",
             reasoning_effort: "high",
+            service_tier: "fast",
             initial_permission_mode: "auto",
             environment: "cloud",
           }),

apps/code/src/renderer/api/posthogClient.ts

@@ -157,11 +157,13 @@ export interface FinalizedTaskArtifactUpload {
 }
 
 type CloudRuntimeAdapter = "claude" | "codex";
+type CloudRunServiceTier = "standard" | "fast" | "flex";
 
 interface CloudRunOptions {
   adapter?: CloudRuntimeAdapter;
   model?: string;
   reasoningLevel?: string;
+  serviceTier?: CloudRunServiceTier;
   sandboxEnvironmentId?: string;
   prAuthorshipMode?: PrAuthorshipMode;
   runSource?: CloudRunSource;
@@ -233,6 +235,9 @@ function buildCloudRunRequestBody(
   if (options?.sandboxEnvironmentId) {
     body.sandbox_environment_id = options.sandboxEnvironmentId;
   }
+  if (options?.serviceTier) {
+    body.service_tier = options.serviceTier;
+  }
   if (options?.prAuthorshipMode) {
     body.pr_authorship_mode = options.prAuthorshipMode;
   }

apps/code/src/renderer/features/message-editor/components/PromptInput.tsx

@@ -40,6 +40,7 @@ export interface PromptInputProps {
   enableCommands?: boolean;
   // toolbar slots
   modelSelector?: React.ReactElement | null | false;
+  speedSelector?: React.ReactElement | null | false;
   reasoningSelector?: React.ReactElement | null | false;
   historyButton?: React.ReactNode;
   // prompt history provider
@@ -80,6 +81,7 @@ export const PromptInput = forwardRef<EditorHandle, PromptInputProps>(
       enableBashMode = false,
       enableCommands = true,
       modelSelector,
+      speedSelector,
       reasoningSelector,
       historyButton,
       getPromptHistory,
@@ -318,6 +320,7 @@ export const PromptInput = forwardRef<EditorHandle, PromptInputProps>(
               />
             )}
             {modelSelector && <span>{modelSelector}</span>}
+            {speedSelector && <span>{speedSelector}</span>}
             {reasoningSelector && <span>{reasoningSelector}</span>}
             {isBashMode && (
               <Text className="font-mono text-(--blue-9) text-[13px]">

apps/code/src/renderer/features/sessions/components/ServiceTierSelector.tsx

@@ -0,0 +1,55 @@
+import type { SessionConfigOption } from "@agentclientprotocol/sdk";
+import { Tooltip } from "@components/ui/Tooltip";
+import { Lightning } from "@phosphor-icons/react";
+import { Button } from "@posthog/quill";
+import { flattenSelectOptions } from "../stores/sessionStore";
+
+interface ServiceTierSelectorProps {
+  serviceTierOption?: SessionConfigOption;
+  onChange?: (value: string) => void;
+  disabled?: boolean;
+}
+
+export function ServiceTierSelector({
+  serviceTierOption,
+  onChange,
+  disabled,
+}: ServiceTierSelectorProps) {
+  if (!serviceTierOption || serviceTierOption.type !== "select") {
+    return null;
+  }
+
+  const options = flattenSelectOptions(serviceTierOption.options);
+  const supportsFastMode = options.some((opt) => opt.value === "fast");
+  if (!supportsFastMode) return null;
+
+  const activeTier = serviceTierOption.currentValue;
+  const fastModeEnabled = activeTier === "fast";
+
+  const handleClick = () => {
+    onChange?.(fastModeEnabled ? "standard" : "fast");
+  };
+
+  return (
+    <Tooltip content="1.5x speed, increased usage" side="top">
+      <span className="inline-flex">
+        <Button
+          type="button"
+          variant="default"
+          size="sm"
+          disabled={disabled}
+          aria-label="Fast Mode"
+          aria-pressed={fastModeEnabled}
+          className={
+            fastModeEnabled
+              ? "border-(--amber-7) bg-(--amber-3) text-amber-11 hover:bg-(--amber-4)"
+              : "text-muted-foreground"
+          }
+          onClick={handleClick}
+        >
+          <Lightning size={14} weight={fastModeEnabled ? "fill" : "regular"} />
+        </Button>
+      </span>
+    </Tooltip>
+  );
+}

apps/code/src/renderer/features/sessions/components/SessionView.tsx

@@ -12,6 +12,7 @@ import {
   useAdapterForTask,
   useModeConfigOptionForTask,
   usePendingPermissionsForTask,
+  useServiceTierConfigOptionForTask,
   useThoughtLevelConfigOptionForTask,
 } from "@features/sessions/stores/sessionStore";
 import type { Plan } from "@features/sessions/types";
@@ -41,6 +42,7 @@ import { ModelSelector } from "./ModelSelector";
 import { PlanStatusBar } from "./PlanStatusBar";
 import { ReasoningLevelSelector } from "./ReasoningLevelSelector";
 import { RawLogsView } from "./raw-logs/RawLogsView";
+import { ServiceTierSelector } from "./ServiceTierSelector";
 
 interface SessionViewProps {
   events: AcpMessage[];
@@ -129,6 +131,7 @@ export function SessionView({
   const pendingPermissions = usePendingPermissionsForTask(taskId);
   const modeOption = useModeConfigOptionForTask(taskId);
   const thoughtOption = useThoughtLevelConfigOptionForTask(taskId);
+  const serviceTierOption = useServiceTierConfigOptionForTask(taskId);
   const adapter = useAdapterForTask(taskId);
   const { allowBypassPermissions } = useSettingsStore();
   const currentModeId = modeOption?.currentValue;
@@ -177,6 +180,18 @@ export function SessionView({
     [taskId, thoughtOption],
   );
 
+  const handleServiceTierChange = useCallback(
+    (value: string) => {
+      if (!taskId || !serviceTierOption) return;
+      getSessionService().setSessionConfigOption(
+        taskId,
+        serviceTierOption.id,
+        value,
+      );
+    },
+    [taskId, serviceTierOption],
+  );
+
   const sessionId = taskId ?? "default";
   const setContext = useDraftStore((s) => s.actions.setContext);
   const requestFocus = useDraftStore((s) => s.actions.requestFocus);
@@ -645,6 +660,15 @@ export function SessionView({
                               />
                             ) : null
                           }
+                          speedSelector={
+                            adapter === "codex" && serviceTierOption ? (
+                              <ServiceTierSelector
+                                serviceTierOption={serviceTierOption}
+                                onChange={handleServiceTierChange}
+                                disabled={!isRunning}
+                              />
+                            ) : null
+                          }
                           onBeforeSubmit={onBeforeSubmit}
                           onSubmit={handleSubmit}
                           onBashCommand={onBashCommand}

apps/code/src/renderer/features/sessions/hooks/useSession.ts

@@ -148,6 +148,13 @@ export const useThoughtLevelConfigOptionForTask = (
   return useConfigOptionForTask(taskId, "thought_level");
 };
 
+/** Get the service tier config option for a task */
+export const useServiceTierConfigOptionForTask = (
+  taskId: string | undefined,
+): SessionConfigOption | undefined => {
+  return useConfigOptionForTask(taskId, "service_tier");
+};
+
 /** Get the adapter type for a task */
 export const useAdapterForTask = (
   taskId: string | undefined,

apps/code/src/renderer/features/sessions/service/service.test.ts

@@ -2489,6 +2489,14 @@ describe("SessionService", () => {
               currentValue: "high",
               options: [],
             },
+            {
+              id: "service_tier",
+              name: "Speed",
+              type: "select",
+              category: "service_tier",
+              currentValue: "fast",
+              options: [],
+            },
           ],
         }),
       );
@@ -2553,6 +2561,7 @@ describe("SessionService", () => {
           adapter: "codex",
           model: "gpt-5.4",
           reasoningLevel: "high",
+          serviceTier: "fast",
           resumeFromRunId: "run-123",
         }),
       );