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feature: add Codex Fast Mode support #2115

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cfa96f2
Add Codex Fast Mode support
cvolzer3 May 8, 2026
147d793
Send Codex service tier to cloud runs
cvolzer3 May 8, 2026
bd3949d
feat: add fast mode slash command
cvolzer3 Jun 15, 2026
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32 changes: 32 additions & 0 deletions packages/agent/src/adapters/codex/codex-agent.refresh.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -110,6 +110,7 @@ type PrivateAgent = {
promptRunning: boolean;
};
sessionId: string;
currentMcpServers: McpServer[];
sessionState: {
sessionId: string;
cwd: string;
Expand All @@ -120,6 +121,7 @@ type PrivateAgent = {
cachedWriteTokens: number;
};
configOptions: unknown[];
serviceTier?: string;
taskRunId?: string;
};
codexProcess: SpawnHandle;
Expand Down Expand Up @@ -286,4 +288,34 @@ describe("CodexAcpAgent.extMethod refresh_session", () => {
expect(spawnedProcesses).toHaveLength(2);
expect(createdConnections[1]?.loadSession).toHaveBeenCalled();
});

it("applies service tier changes by respawning with the current MCP servers", async () => {
const agent = makeAgent();
const { priv } = primeSession(agent, "s-4");
const mcpServers: McpServer[] = [
{ name: "posthog", type: "http", url: "https://mcp", headers: [] },
];
priv.currentMcpServers = mcpServers;

const response = await agent.setSessionConfigOption({
sessionId: "s-4",
configId: "service_tier",
value: "fast",
} as never);

expect(hoisted.spawnCodexProcessMock).toHaveBeenLastCalledWith(
expect.objectContaining({ serviceTier: "fast" }),
);
expect(createdConnections[1]?.loadSession).toHaveBeenCalledWith({
sessionId: "s-4",
cwd: "/tmp/repo",
mcpServers,
});
expect(response.configOptions).toContainEqual(
expect.objectContaining({
id: "service_tier",
currentValue: "fast",
}),
);
});
});
27 changes: 27 additions & 0 deletions packages/agent/src/adapters/codex/codex-agent.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ import type {
NewSessionResponse,
} from "@agentclientprotocol/sdk";
import { beforeEach, describe, expect, it, vi } from "vitest";
import type { CodexProcessOptions } from "./spawn";

const mockCodexConnection = {
initialize: vi.fn(),
Expand Down Expand Up @@ -69,6 +70,7 @@ describe("CodexAcpAgent", () => {
overrides: Partial<AgentSideConnection> = {},
agentOptions?: {
onStructuredOutput?: (output: Record<string, unknown>) => Promise<void>;
codexProcessOptions?: Partial<CodexProcessOptions>;
},
): {
agent: CodexAcpAgent;
Expand All @@ -89,6 +91,7 @@ describe("CodexAcpAgent", () => {
const agent = new CodexAcpAgent(client, {
codexProcessOptions: {
cwd: process.cwd(),
...agentOptions?.codexProcessOptions,
},
onStructuredOutput: agentOptions?.onStructuredOutput,
});
Expand Down Expand Up @@ -118,6 +121,30 @@ describe("CodexAcpAgent", () => {
).toBe("read-only");
});

it("adds the Codex service tier option to new sessions", async () => {
const { agent } = createAgent(
{},
{ codexProcessOptions: { serviceTier: "fast" } },
);
mockCodexConnection.newSession.mockResolvedValue({
sessionId: "session-1",
modes: { currentModeId: "auto", availableModes: [] },
configOptions: [],
} satisfies Partial<NewSessionResponse>);

const response = await agent.newSession({
cwd: process.cwd(),
} as never);

expect(response.configOptions).toContainEqual(
expect.objectContaining({
id: "service_tier",
category: "service_tier",
currentValue: "fast",
}),
);
});

it("propagates taskRunId and fires SDK_SESSION when loading a cloud session", async () => {
const { agent, client } = createAgent();
mockCodexConnection.loadSession.mockResolvedValue({
Expand Down
148 changes: 143 additions & 5 deletions packages/agent/src/adapters/codex/codex-agent.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@ import {
RequestError,
type ResumeSessionRequest,
type ResumeSessionResponse,
type SessionConfigOption,
type SetSessionConfigOptionRequest,
type SetSessionConfigOptionResponse,
type SetSessionModeRequest,
Expand Down Expand Up @@ -123,6 +124,31 @@ interface NewSessionMeta {
jsonSchema?: Record<string, unknown> | null;
}

type CodexServiceTier = "standard" | "fast" | "flex";

const CODEX_SERVICE_TIER_CONFIG_ID = "service_tier";
const CODEX_SERVICE_TIER_OPTIONS: Array<{
value: CodexServiceTier;
name: string;
description: string;
}> = [
{
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",
},
];

export interface CodexAcpAgentOptions {
codexProcessOptions: CodexProcessOptions;
processCallbacks?: ProcessSpawnedCallback;
Expand All @@ -142,6 +168,38 @@ function toCodexPermissionMode(mode?: string): PermissionMode {
return "auto";
}

function toCodexServiceTier(serviceTier?: string | null): CodexServiceTier {
switch (serviceTier?.toLowerCase()) {
case "fast":
case "priority":
return "fast";
case "flex":
return "flex";
default:
return "standard";
}
}

function codexServiceTierConfigValue(
serviceTier: CodexServiceTier,
): string | undefined {
return serviceTier === "standard" ? undefined : serviceTier;
}

function codexServiceTierConfigOption(
currentValue: CodexServiceTier,
): SessionConfigOption {
return {
id: CODEX_SERVICE_TIER_CONFIG_ID,
name: "Speed",
type: "select",
category: "service_tier",
currentValue,
options: CODEX_SERVICE_TIER_OPTIONS,
description: "Choose the Codex service tier for new turns",
} as SessionConfigOption;
}

/**
* Prepend `_meta.prContext` (set by the agent-server on Slack-originated
* follow-up runs) to the prompt as a text block, mirroring Claude's
Expand Down Expand Up @@ -313,6 +371,7 @@ export class CodexAcpAgent extends BaseAcpAgent {
private readonly onStructuredOutput?: (
output: Record<string, unknown>,
) => Promise<void>;
private currentMcpServers: McpServer[] = [];
// Snapshot of the initialize() request so refreshSession can replay the
// same handshake against a respawned codex-acp subprocess.
private lastInitRequest?: InitializeRequest;
Expand Down Expand Up @@ -413,9 +472,10 @@ export class CodexAcpAgent extends BaseAcpAgent {
meta,
);
const response = await this.codexConnection.newSession(injectedParams);
response.configOptions = normalizeCodexConfigOptions(
response.configOptions = this.normalizeConfigOptions(
response.configOptions,
);
this.currentMcpServers = injectedParams.mcpServers ?? [];

// Initialize session state. Mutate in place — codex-client closure-
// captured this object in the constructor and writes contextUsed/
Expand All @@ -426,6 +486,7 @@ export class CodexAcpAgent extends BaseAcpAgent {
modeId: response.modes?.currentModeId ?? "auto",
modelId: modelIdFromConfigOptions(response.configOptions),
permissionMode: requestedPermissionMode,
serviceTier: this.currentServiceTier(),
});
this.sessionId = response.sessionId;
this.sessionState.configOptions = response.configOptions ?? [];
Expand Down Expand Up @@ -461,9 +522,10 @@ export class CodexAcpAgent extends BaseAcpAgent {
meta,
);
const response = await this.codexConnection.loadSession(injectedParams);
response.configOptions = normalizeCodexConfigOptions(
response.configOptions = this.normalizeConfigOptions(
response.configOptions,
);
this.currentMcpServers = injectedParams.mcpServers ?? [];
const currentPermissionMode = getCurrentPermissionMode(
response.modes?.currentModeId,
meta?.permissionMode,
Expand All @@ -478,6 +540,7 @@ export class CodexAcpAgent extends BaseAcpAgent {
taskId: resolveTaskId(meta),
modeId: response.modes?.currentModeId ?? "auto",
permissionMode: currentPermissionMode,
serviceTier: this.currentServiceTier(),
});
this.sessionId = params.sessionId;
this.sessionState.configOptions = response.configOptions ?? [];
Expand Down Expand Up @@ -513,9 +576,10 @@ export class CodexAcpAgent extends BaseAcpAgent {

// codex-acp doesn't support resume natively, use loadSession instead
const loadResponse = await this.codexConnection.loadSession(injectedParams);
loadResponse.configOptions = normalizeCodexConfigOptions(
loadResponse.configOptions = this.normalizeConfigOptions(
loadResponse.configOptions,
);
this.currentMcpServers = injectedParams.mcpServers ?? [];
const currentPermissionMode = getCurrentPermissionMode(
loadResponse.modes?.currentModeId,
meta?.permissionMode,
Expand All @@ -525,6 +589,7 @@ export class CodexAcpAgent extends BaseAcpAgent {
taskId: resolveTaskId(meta),
modeId: loadResponse.modes?.currentModeId ?? "auto",
permissionMode: currentPermissionMode,
serviceTier: this.currentServiceTier(),
});
this.sessionId = params.sessionId;
this.sessionState.configOptions = loadResponse.configOptions ?? [];
Expand Down Expand Up @@ -562,16 +627,18 @@ export class CodexAcpAgent extends BaseAcpAgent {

// Create a new session via codex-acp (fork isn't natively supported)
const newResponse = await this.codexConnection.newSession(injectedParams);
newResponse.configOptions = normalizeCodexConfigOptions(
newResponse.configOptions = this.normalizeConfigOptions(
newResponse.configOptions,
);
this.currentMcpServers = injectedParams.mcpServers ?? [];

const requestedPermissionMode = toCodexPermissionMode(meta?.permissionMode);
resetSessionState(this.sessionState, newResponse.sessionId, params.cwd, {
taskRunId: meta?.taskRunId,
taskId: resolveTaskId(meta),
modeId: newResponse.modes?.currentModeId ?? "auto",
permissionMode: requestedPermissionMode,
serviceTier: this.currentServiceTier(),
});
this.sessionId = newResponse.sessionId;
this.sessionState.configOptions = newResponse.configOptions ?? [];
Expand All @@ -586,6 +653,38 @@ export class CodexAcpAgent extends BaseAcpAgent {
return newResponse;
}

private currentServiceTier(): CodexServiceTier {
return toCodexServiceTier(this.codexProcessOptions.serviceTier);
}

private withCodexServiceTierOption(
configOptions: SessionConfigOption[] | null | undefined,
): SessionConfigOption[] {
const serviceTierOption = codexServiceTierConfigOption(
this.currentServiceTier(),
);
const options = configOptions ?? [];
const existingIndex = options.findIndex(
(option) => option.id === CODEX_SERVICE_TIER_CONFIG_ID,
);

if (existingIndex === -1) {
return [...options, serviceTierOption];
}

return options.map((option, index) =>
index === existingIndex ? serviceTierOption : option,
);
}

private normalizeConfigOptions(
configOptions: SessionConfigOption[] | null | undefined,
): SessionConfigOption[] {
return this.withCodexServiceTierOption(
normalizeCodexConfigOptions(configOptions) ?? [],
);
}

/**
* When the caller wires up `onStructuredOutput` and provides a JSON schema
* via `_meta.jsonSchema`, inject the stdio MCP server that exposes
Expand Down Expand Up @@ -909,6 +1008,7 @@ export class CodexAcpAgent extends BaseAcpAgent {
cwd: this.sessionState.cwd,
mcpServers,
});
this.currentMcpServers = mcpServers;

// Swap everything at once so closeSession/prompt/cancel target the new
// subprocess going forward. Preserve sessionState (accumulatedUsage,
Expand Down Expand Up @@ -936,12 +1036,50 @@ export class CodexAcpAgent extends BaseAcpAgent {
return response ?? {};
}

private async setServiceTier(value: string): Promise<SessionConfigOption[]> {
const previousTier = this.currentServiceTier();
const nextTier = toCodexServiceTier(value);
if (previousTier === nextTier) {
this.sessionState.serviceTier = nextTier;
this.sessionState.configOptions = this.withCodexServiceTierOption(
this.sessionState.configOptions,
);
return this.sessionState.configOptions;
}

const previousConfigValue = this.codexProcessOptions.serviceTier;
this.codexProcessOptions.serviceTier =
codexServiceTierConfigValue(nextTier);

try {
await this.refreshSession(this.currentMcpServers);
} catch (error) {
this.codexProcessOptions.serviceTier = previousConfigValue;
this.sessionState.serviceTier = previousTier;
this.sessionState.configOptions = this.withCodexServiceTierOption(
this.sessionState.configOptions,
);
throw error;
}

this.sessionState.serviceTier = nextTier;
this.sessionState.configOptions = this.withCodexServiceTierOption(
this.sessionState.configOptions,
Comment on lines +1057 to +1067

@greptile-apps greptile-apps Bot Jun 15, 2026

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P2 Duplicate "priority" alias in two normalizers

toCodexServiceTier here and normalizeServiceTier in spawn.ts both independently map "priority" → "fast". If a new alias or tier is added, both functions must be updated in sync. The canonical mapping belongs in one place — the spawn.ts normalizer that actually writes the flag to the process args is the logical owner; toCodexServiceTier could delegate to it (or to a shared helper) rather than re-implementing the same switch.

Prompt To Fix With AI 
This is a comment left during a code review.
Path: packages/agent/src/adapters/codex/codex-agent.ts
Line: 899-909

Comment:
**Duplicate "priority" alias in two normalizers**

`toCodexServiceTier` here and `normalizeServiceTier` in `spawn.ts` both independently map `"priority"` → `"fast"`. If a new alias or tier is added, both functions must be updated in sync. The canonical mapping belongs in one place — the `spawn.ts` normalizer that actually writes the flag to the process args is the logical owner; `toCodexServiceTier` could delegate to it (or to a shared helper) rather than re-implementing the same switch.

How can I resolve this? If you propose a fix, please make it concise.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

);
return this.sessionState.configOptions;
}

async setSessionConfigOption(
params: SetSessionConfigOptionRequest,
): Promise<SetSessionConfigOptionResponse> {
if (params.configId === CODEX_SERVICE_TIER_CONFIG_ID) {
const configOptions = await this.setServiceTier(String(params.value));
return { configOptions };
}

const response = await this.codexConnection.setSessionConfigOption(params);
if (response.configOptions) {
response.configOptions = normalizeCodexConfigOptions(
response.configOptions = this.normalizeConfigOptions(
response.configOptions,
) as typeof response.configOptions;
this.sessionState.configOptions = response.configOptions;
Expand Down
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