diff --git a/src/CodexAcpServer.ts b/src/CodexAcpServer.ts
index ead7814d2..5db6e699d 100644
--- a/src/CodexAcpServer.ts
+++ b/src/CodexAcpServer.ts
@@ -840,6 +840,7 @@ export class CodexAcpServer {
             sessionId,
             sessionState.cwd,
             () => sessionState.sessionTitleSource,
+            () => this.authProviderUsesOpenAiAccount(sessionState.authProvider),
         );
         this.installSessionState(sessionState);
         resumeSubscribed = false;
@@ -2267,6 +2268,7 @@ export class CodexAcpServer {
             sessionId,
             sessionState.cwd,
             () => sessionState.sessionTitleSource,
+            () => this.authProviderUsesOpenAiAccount(sessionState.authProvider),
         );
         this.installSessionState(sessionState);
         if (knownAccount === "pending") {
diff --git a/src/TitleGenerator.ts b/src/TitleGenerator.ts
index 76f573898..74f2ff48e 100644
--- a/src/TitleGenerator.ts
+++ b/src/TitleGenerator.ts
@@ -39,6 +39,7 @@ export class TitleGenerator {
         private readonly mainThreadId: string,
         private readonly cwd: string,
         private readonly getSessionTitleSource: () => string,
+        private readonly sessionUsesOpenAiProvider: () => boolean,
     ) {}
 
     /**
@@ -62,7 +63,8 @@ export class TitleGenerator {
 
     /**
      * Fire-and-forget hook — call after each turn completes.
-     * Only acts on the first call for new sessions without an existing title.
+     * Only acts on the first call for new sessions without an existing title,
+     * and only when the session uses the OpenAI provider, which serves the title model.
      *
      * @param userPromptText  The text of the user's first message (from params.prompt,
      *                        not turn.items — turn.items contains only agent output).
@@ -74,6 +76,7 @@ export class TitleGenerator {
         // "unknown": resumed session with indeterminate history — skip
         if (src === "explicit" || src === "unknown") return;
         this.generated = true;
+        if (!this.sessionUsesOpenAiProvider()) return;
         const run = this.generateAndPersist(userPromptText)
             .catch(() => {
                 // title generation is best-effort; never surface errors to the user
diff --git a/src/__tests__/CodexACPAgent/title-generation-provider.test.ts b/src/__tests__/CodexACPAgent/title-generation-provider.test.ts
new file mode 100644
index 000000000..473a4d176
--- /dev/null
+++ b/src/__tests__/CodexACPAgent/title-generation-provider.test.ts
@@ -0,0 +1,49 @@
+import {describe, expect, it, vi} from "vitest";
+import type {Turn} from "../../app-server/v2";
+import {ModelId} from "../../ModelId";
+import {createCodexMockTestFixture, createTestModel} from "../acp-test-utils";
+
+const sessionId = "title-session";
+const turnId = "title-turn";
+
+describe("AI session title generation", () => {
+    it.each([
+        ["openai", 1],
+        ["fleet-gateway", 0],
+    ])("for a new session on the %s provider runs %i title turn(s)", async (modelProvider, titleTurns) => {
+        const fixture = createCodexMockTestFixture();
+        const agent = fixture.getCodexAcpAgent();
+        const client = fixture.getCodexAcpClient();
+        const appServer = fixture.getCodexAppServerClient();
+        const model = createTestModel();
+        vi.spyOn(client, "readAuthRequirement").mockResolvedValue({required: false, account: null});
+        vi.spyOn(client, "getAccount").mockResolvedValue({account: {type: "apiKey"}, requiresOpenaiAuth: false});
+        vi.spyOn(client, "listSkills").mockResolvedValue({data: []});
+        vi.spyOn(client, "newSession").mockResolvedValue({
+            sessionId,
+            currentModelId: ModelId.create(model.id, model.defaultReasoningEffort).toString(),
+            models: [model],
+            collaborationMode: "default",
+            modelProvider,
+            additionalDirectories: [],
+        });
+        vi.spyOn(appServer, "turnStart").mockResolvedValue({turn: createTurn("inProgress")});
+        vi.spyOn(appServer, "awaitTurnCompleted").mockResolvedValue({threadId: sessionId, turn: createTurn("completed")});
+        const threadStart = vi.spyOn(appServer, "threadStart")
+            .mockResolvedValue({thread: {id: "title-thread"}} as Awaited<ReturnType<typeof appServer.threadStart>>);
+        const runTurn = vi.spyOn(appServer, "runTurn");
+
+        await agent.newSession({cwd: "/workspace", mcpServers: []});
+        await agent.prompt({sessionId, prompt: [{type: "text", text: "Fix the failing build"}]});
+        await agent.getSessionState(sessionId).titleGen?.waitForIdle(1_000);
+
+        expect(threadStart).toHaveBeenCalledTimes(titleTurns);
+        const titleTurnRequests = runTurn.mock.calls.filter(([params]) => params.threadId === "title-thread");
+        expect(titleTurnRequests).toHaveLength(titleTurns);
+        expect(titleTurnRequests.map(([params]) => params.model)).toEqual(titleTurns === 0 ? [] : ["gpt-5.6-luna"]);
+    });
+});
+
+function createTurn(status: Turn["status"]): Turn {
+    return {id: turnId, items: [], itemsView: "full", status, error: null, startedAt: null, completedAt: null, durationMs: null};
+}
diff --git a/src/__tests__/TitleGenerator.test.ts b/src/__tests__/TitleGenerator.test.ts
index 70aaaeed9..4395d80dc 100644
--- a/src/__tests__/TitleGenerator.test.ts
+++ b/src/__tests__/TitleGenerator.test.ts
@@ -3,8 +3,14 @@ import {TitleGenerator} from "../TitleGenerator";
 import type {CodexAppServerClient} from "../CodexAppServerClient";
 import {deferred} from "./acp-test-utils";
 
-function createGenerator(client: Partial<CodexAppServerClient>) {
-    return new TitleGenerator(client as CodexAppServerClient, "thread-id", "/test/cwd", () => "unset");
+function createGenerator(client: Partial<CodexAppServerClient>, sessionUsesOpenAiProvider = true) {
+    return new TitleGenerator(
+        client as CodexAppServerClient,
+        "thread-id",
+        "/test/cwd",
+        () => "unset",
+        () => sessionUsesOpenAiProvider,
+    );
 }
 
 describe("TitleGenerator.waitForIdle", () => {
@@ -87,3 +93,30 @@ describe("TitleGenerator prompt", () => {
         expect(text.endsWith(`User's first message:\n${"a".repeat(3_999)}`)).toBe(true);
     });
 });
+
+describe("TitleGenerator model provider", () => {
+    it("requests a title from the title model for a session on the OpenAI provider", async () => {
+        const threadStart = vi.fn().mockResolvedValue({thread: {id: "ephemeral"}});
+        const runTurn = vi.fn().mockResolvedValue({turn: {items: []}});
+        const generator = createGenerator({threadStart, runTurn} as unknown as Partial<CodexAppServerClient>);
+
+        generator.onTurnCompleted("hello");
+        await generator.waitForIdle(1_000);
+
+        expect(threadStart).toHaveBeenCalledWith({cwd: "/test/cwd", ephemeral: true});
+        expect(runTurn).toHaveBeenCalledWith(expect.objectContaining({threadId: "ephemeral", model: "gpt-5.6-luna"}));
+    });
+
+    it("starts no title thread or turn for a session on another provider", async () => {
+        const threadStart = vi.fn().mockResolvedValue({thread: {id: "ephemeral"}});
+        const runTurn = vi.fn().mockResolvedValue({turn: {items: []}});
+        const generator = createGenerator({threadStart, runTurn} as unknown as Partial<CodexAppServerClient>, false);
+
+        generator.onTurnCompleted("hello");
+        generator.onTurnCompleted("second turn");
+        await generator.waitForIdle(1_000);
+
+        expect(threadStart).not.toHaveBeenCalled();
+        expect(runTurn).not.toHaveBeenCalled();
+    });
+});