feat: LLM-26878 Add “Fast” mode for Codex-agent

src/CodexAcpClient.ts

@@ -13,6 +13,7 @@ import type {Disposable} from "vscode-jsonrpc";
 import type {
     ClientInfo,
     ReasoningEffort,
+    ServiceTier,
     ServerNotification
 } from "./app-server";
 import type {JsonValue} from "./app-server/serde_json/JsonValue";
@@ -220,6 +221,7 @@ export class CodexAcpClient {
             sessionId: request.sessionId,
             currentModelId: currentModelId,
             models: codexModels,
+            currentServiceTier: response.serviceTier ?? null,
         }
     }
 
@@ -242,6 +244,7 @@ export class CodexAcpClient {
             sessionId: request.sessionId,
             currentModelId: currentModelId,
             models: codexModels,
+            currentServiceTier: response.serviceTier ?? null,
             thread: response.thread,
         };
     }
@@ -271,6 +274,7 @@ export class CodexAcpClient {
             sessionId: response.thread.id,
             currentModelId: currentModelId,
             models: codexModels,
+            currentServiceTier: response.serviceTier ?? null,
         };
     }
 
@@ -394,6 +398,7 @@ export class CodexAcpClient {
         request: acp.PromptRequest,
         agentMode: AgentMode,
         modelId: ModelId,
+        serviceTier: ServiceTier | null,
         disableSummary: boolean,
         cwd: string,
     ): Promise<TurnCompletedNotification> {
@@ -412,6 +417,7 @@ export class CodexAcpClient {
             cwd: null,
             effort: effort,
             model: modelId.model,
+            serviceTier: serviceTier,
         });
     }
 
@@ -605,6 +611,7 @@ export type SessionMetadata = {
     sessionId: string,
     currentModelId: string,
     models: Model[],
+    currentServiceTier?: ServiceTier | null,
 }
 
 export type SessionMetadataWithThread = SessionMetadata & {

src/CodexAcpServer.ts

@@ -32,6 +32,14 @@ import {
     createFileChangeUpdate,
     createMcpToolCallUpdate,
 } from "./CodexToolCallMapper";
+import {
+    createFastModeConfigOption,
+    FAST_MODE_CONFIG_ID,
+    FAST_MODE_OFF,
+    FAST_MODE_ON,
+    modelSupportsFast,
+    resolveFastServiceTier,
+} from "./FastModeConfig";
 
 export interface SessionState {
     sessionId: string,
@@ -46,6 +54,8 @@ export interface SessionState {
     rateLimits: RateLimitsMap | null;
     account: Account | null;
     cwd: string;
+    fastModeEnabled: boolean;
+    currentModelSupportsFast: boolean;
     sessionMcpServers?: Array<string>;
 }
 
@@ -163,6 +173,7 @@ export class CodexAcpServer implements acp.Agent {
         const {sessionId, currentModelId, models} = sessionMetadata;
         const sessionMcpServers = this.resolveSessionMcpServers(requestedMcpServers, "sessionId" in request);
         const currentModel = this.findCurrentModel(models, currentModelId);
+        const currentModelSupportsFast = modelSupportsFast(currentModel);
         const sessionState: SessionState = {
             sessionId: sessionId,
             currentModelId: currentModelId,
@@ -176,6 +187,8 @@ export class CodexAcpServer implements acp.Agent {
             rateLimits: null,
             account: account,
             cwd: request.cwd,
+            fastModeEnabled: sessionMetadata.currentServiceTier === "fast",
+            currentModelSupportsFast: currentModelSupportsFast,
             sessionMcpServers: sessionMcpServers,
         }
         this.sessions.set(sessionId, sessionState);
@@ -221,7 +234,8 @@ export class CodexAcpServer implements acp.Agent {
         });
         return {
             models: modelState,
-            modes: modeState
+            modes: modeState,
+            configOptions: this.createSessionConfigOptions(this.getSessionState(sessionId)),
         };
     }
 
@@ -236,7 +250,8 @@ export class CodexAcpServer implements acp.Agent {
         });
         return {
             models: modelState,
-            modes: modeState
+            modes: modeState,
+            configOptions: this.createSessionConfigOptions(this.getSessionState(sessionId)),
         };
     }
 
@@ -261,7 +276,8 @@ export class CodexAcpServer implements acp.Agent {
         return {
             sessionId: sessionId,
             models: modelState,
-            modes: modeState
+            modes: modeState,
+            configOptions: this.createSessionConfigOptions(this.getSessionState(sessionId)),
         };
     }
 
@@ -302,6 +318,28 @@ export class CodexAcpServer implements acp.Agent {
         return {};
     }
 
+    async setSessionConfigOption(params: acp.SetSessionConfigOptionRequest): Promise<acp.SetSessionConfigOptionResponse> {
+        logger.log("Set session config option requested", {
+            sessionId: params.sessionId,
+            configId: params.configId,
+        });
+        const sessionState = this.sessions.get(params.sessionId);
+        if (!sessionState) throw new Error(`Session ${params.sessionId} not found`);
+
+        if (params.configId !== FAST_MODE_CONFIG_ID || ("type" in params && params.type === "boolean")) {
+            throw RequestError.invalidParams();
+        }
+
+        if (params.value !== FAST_MODE_ON && params.value !== FAST_MODE_OFF) {
+            throw RequestError.invalidParams();
+        }
+
+        sessionState.fastModeEnabled = params.value === FAST_MODE_ON;
+        return {
+            configOptions: this.createSessionConfigOptions(sessionState),
+        };
+    }
+
     async unstable_setSessionModel(params: acp.SetSessionModelRequest): Promise<acp.SetSessionModelResponse | void> {
         logger.log("Set session model requested", {
             sessionId: params.sessionId,
@@ -337,10 +375,17 @@ export class CodexAcpServer implements acp.Agent {
         sessionState.currentModelId = ModelId.fromComponents(model, reasoningEffort).toString();
         sessionState.supportedReasoningEfforts = model.supportedReasoningEfforts;
         sessionState.supportedInputModalities = model.inputModalities;
+        sessionState.currentModelSupportsFast = modelSupportsFast(model);
 
         return {};
     }
 
+    private createSessionConfigOptions(sessionState: SessionState): Array<acp.SessionConfigOption> {
+        return [
+            createFastModeConfigOption(sessionState.fastModeEnabled),
+        ];
+    }
+
     private publishAvailableCommandsAsync(sessionId: string) {
         void this.availableCommands.publish(sessionId);
     }
@@ -388,6 +433,7 @@ export class CodexAcpServer implements acp.Agent {
         const {sessionId, currentModelId, models, thread} = sessionMetadata;
         const sessionMcpServers = this.resolveSessionMcpServers(requestedMcpServers, true);
         const currentModel = this.findCurrentModel(models, currentModelId);
+        const currentModelSupportsFast = modelSupportsFast(currentModel);
         const sessionState: SessionState = {
             sessionId: sessionId,
             currentModelId: currentModelId,
@@ -401,6 +447,8 @@ export class CodexAcpServer implements acp.Agent {
             rateLimits: null,
             account: account,
             cwd: request.cwd,
+            fastModeEnabled: sessionMetadata.currentServiceTier === "fast",
+            currentModelSupportsFast: currentModelSupportsFast,
             sessionMcpServers: sessionMcpServers,
         };
         this.sessions.set(sessionId, sessionState);
@@ -767,8 +815,12 @@ export class CodexAcpServer implements acp.Agent {
                 throw RequestError.invalidRequest("The current model does not support image input");
             }
             const agentMode = sessionState.agentMode;
+            const serviceTier = resolveFastServiceTier(
+                sessionState.fastModeEnabled,
+                sessionState.currentModelSupportsFast,
+            );
             const turnCompleted = await this.runWithProcessCheck(
-                () => this.codexAcpClient.sendPrompt(params, agentMode, modelId, disableSummary, sessionState.cwd));
+                () => this.codexAcpClient.sendPrompt(params, agentMode, modelId, serviceTier, disableSummary, sessionState.cwd));
 
             // Check if turn was interrupted (cancelled)
             if (turnCompleted.turn.status === "interrupted") {

src/FastModeConfig.ts

@@ -0,0 +1,40 @@
+import type {SessionConfigOption} from "@agentclientprotocol/sdk";
+import type {ServiceTier} from "./app-server";
+import type {Model} from "./app-server/v2";
+
+export const FAST_MODE_CONFIG_ID = "fast-mode";
+export const FAST_MODE_ON = "on";
+export const FAST_MODE_OFF = "off";
+
+const FAST_MODE_DESCRIPTION = "1.5x speed, increased usage";
+
+export function modelSupportsFast(model: Model | undefined): boolean {
+    return model?.additionalSpeedTiers?.includes("fast") ?? false;
+}
+
+export function resolveFastServiceTier(fastModeEnabled: boolean, currentModelSupportsFast: boolean): ServiceTier | null {
+    return fastModeEnabled && currentModelSupportsFast ? "fast" : null;
+}
+
+export function createFastModeConfigOption(fastModeEnabled: boolean): SessionConfigOption {
+    return {
+        id: FAST_MODE_CONFIG_ID,
+        name: "Fast mode",
+        description: FAST_MODE_DESCRIPTION,
+        category: FAST_MODE_CONFIG_ID,
+        type: "select",
+        currentValue: fastModeEnabled ? FAST_MODE_ON : FAST_MODE_OFF,
+        options: [
+            {
+                value: FAST_MODE_OFF,
+                name: "Off",
+                description: "Default speed, normal usage",
+            },
+            {
+                value: FAST_MODE_ON,
+                name: "On",
+                description: FAST_MODE_DESCRIPTION,
+            },
+        ],
+    };
+}

src/__tests__/CodexACPAgent/data/send-attachments-turn-start.json

@@ -56,7 +56,8 @@
     "personality": null,
     "cwd": "cwd",
     "effort": "effort",
-    "model": "model"
+    "model": "model",
+    "serviceTier": null
   }
 }
 {