Update models used when in copilot provider mode

ts/config.sample.yaml

@@ -160,8 +160,8 @@ openAI:
 # --- Copilot (Copilot SDK chat + Copilot embeddings) -----------------------
 # modelProvider: copilot
 # copilot:
-#   defaultModel: gpt-5.6-luna       # requires an authenticated `copilot` CLI
-#   fallbackModels:                 # first available concrete model is used
+#   defaultModel: gpt-6-luna         # requires an authenticated `copilot` CLI
+#   fallbackModels:                 # after the matching GPT-5.6 tier, use the first available model
 #     - gpt-5.4-mini
 #     - gpt-5-mini
 #     - gpt-5.4

ts/packages/aiclient/src/copilotModelDefaults.ts

@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
-export const DEFAULT_COPILOT_MODEL = "gpt-5.6-luna";
+export const DEFAULT_COPILOT_MODEL = "gpt-6-luna";
 
 export const DEFAULT_COPILOT_FALLBACK_MODELS: readonly string[] = [
     "gpt-5.4-mini",

ts/packages/aiclient/src/copilotModels.ts

@@ -535,6 +535,12 @@ export function selectCopilotModel(
     const requestedModel = byId.get(requested);
     if (requestedModel !== undefined) return requestedModel;
 
+    const previousTier = /^gpt-6-(luna|sol)$/.exec(requested)?.[1];
+    if (previousTier !== undefined) {
+        const previousModel = byId.get(`gpt-5.6-${previousTier}`);
+        if (previousModel !== undefined) return previousModel;
+    }
+
     for (const fallback of fallbackModels) {
         const fallbackModel = byId.get(fallback);
         if (fallbackModel !== undefined) return fallbackModel;

ts/packages/aiclient/src/providerMode.ts

@@ -81,13 +81,13 @@ export function usesProviderDefault(canonical: string): boolean {
  */
 const COPILOT_MAP: Record<CanonicalName, string> = {
     DEFAULT: DEFAULT_COPILOT_MODEL,
-    GPT_35_TURBO: "gpt-5.6-luna",
-    GPT_4_O: "gpt-5.6-sol",
-    GPT_5: "gpt-5.6-sol",
-    GPT_5_MINI: "gpt-5.6-terra",
-    GPT_5_NANO: "gpt-5.6-luna",
-    GPT_5_6_LUNA: "gpt-5.6-luna",
-    GPT_V: "gpt-5.6-sol",
+    GPT_35_TURBO: "gpt-6-luna",
+    GPT_4_O: "gpt-6-sol",
+    GPT_5: "gpt-6-sol",
+    GPT_5_MINI: "gpt-6-luna",
+    GPT_5_NANO: "gpt-6-luna",
+    GPT_5_6_LUNA: "gpt-6-luna",
+    GPT_V: "gpt-6-sol",
 };
 
 const OLLAMA_MAP: Record<CanonicalName, string> = {

ts/packages/aiclient/test/copilotTransport.spec.ts

@@ -275,11 +275,39 @@ describe("Copilot session fallback", () => {
 describe("selectCopilotModel", () => {
     test("uses the requested model when it is available", () => {
         const selected = selectCopilotModel(
-            "gpt-5.6-luna",
+            "gpt-6-luna",
+            ["gpt-5.4-mini"],
+            [
+                makeModel("gpt-5.4-mini"),
+                makeModel("gpt-5.6-luna"),
+                makeModel("gpt-6-luna"),
+            ],
+        );
+        expect(selected?.id).toBe("gpt-6-luna");
+    });
+
+    test.each(["luna", "sol"])(
+        "uses GPT-5.6 %s before generic fallbacks when GPT-6 is unavailable",
+        (tier) => {
+            const selected = selectCopilotModel(
+                `gpt-6-${tier}`,
+                ["gpt-5.4-mini"],
+                [makeModel("gpt-5.4-mini"), makeModel(`gpt-5.6-${tier}`)],
+            );
+            expect(selected?.id).toBe(`gpt-5.6-${tier}`);
+        },
+    );
+
+    test("skips a disabled GPT-5.6 tier fallback", () => {
+        const selected = selectCopilotModel(
+            "gpt-6-luna",
             ["gpt-5.4-mini"],
-            [makeModel("gpt-5.4-mini"), makeModel("gpt-5.6-luna")],
+            [
+                makeModel("gpt-5.6-luna", { policy: "disabled" }),
+                makeModel("gpt-5.4-mini"),
+            ],
         );
-        expect(selected?.id).toBe("gpt-5.6-luna");
+        expect(selected?.id).toBe("gpt-5.4-mini");
     });
 
     test("uses the first configured concrete fallback", () => {

ts/packages/aiclient/test/providerMode.spec.ts

@@ -39,15 +39,15 @@ describe("Copilot provider mode", () => {
     });
 
     test.each([
-        ["DEFAULT", "gpt-5.6-luna"],
-        ["GPT_35_TURBO", "gpt-5.6-luna"],
-        ["GPT_4_O", "gpt-5.6-sol"],
-        ["GPT_5", "gpt-5.6-sol"],
-        ["GPT_5_MINI", "gpt-5.6-terra"],
-        ["GPT_5_NANO", "gpt-5.6-luna"],
-        ["GPT_5_6_LUNA", "gpt-5.6-luna"],
-        ["gpt_5_6_luna", "gpt-5.6-luna"],
-        ["GPT_V", "gpt-5.6-sol"],
+        ["DEFAULT", "gpt-6-luna"],
+        ["GPT_35_TURBO", "gpt-6-luna"],
+        ["GPT_4_O", "gpt-6-sol"],
+        ["GPT_5", "gpt-6-sol"],
+        ["GPT_5_MINI", "gpt-6-luna"],
+        ["GPT_5_NANO", "gpt-6-luna"],
+        ["GPT_5_6_LUNA", "gpt-6-luna"],
+        ["gpt_5_6_luna", "gpt-6-luna"],
+        ["GPT_V", "gpt-6-sol"],
     ])("maps %s to %s", (canonical, expected) => {
         expect(resolveTarget("copilot", canonical)).toBe(expected);
     });

ts/packages/dispatcher/dispatcher/test/sessionModelDefaults.spec.ts

@@ -5,21 +5,24 @@ import { openai, resolveTarget } from "@typeagent/aiclient";
 import { Session } from "../src/context/session.js";
 
 describe("session translation model", () => {
-    test("defaults to GPT_5_6_LUNA and resolves to Luna in Copilot mode", async () => {
+    test("defaults to GPT_5_6_LUNA and resolves to GPT-6 Luna in Copilot mode", async () => {
         const session = await Session.create();
         const model = session.getConfig().translation.model;
         expect(model).toBe(openai.GPT_5_6_LUNA);
-        expect(resolveTarget("copilot", model)).toBe("gpt-5.6-luna");
+        expect(resolveTarget("copilot", model)).toBe("gpt-6-luna");
     });
 
     test("preserves an explicit model and restores Luna on reset", async () => {
         const session = await Session.create({
             translation: { model: "GPT_4_O" },
         });
         expect(session.getConfig().translation.model).toBe("GPT_4_O");
-        expect(resolveTarget("copilot", "GPT_4_O")).toBe("gpt-5.6-sol");
+        expect(resolveTarget("copilot", "GPT_4_O")).toBe("gpt-6-sol");
 
         session.updateSettings({ translation: { model: null } });
         expect(session.getConfig().translation.model).toBe(openai.GPT_5_6_LUNA);
+        expect(
+            resolveTarget("copilot", session.getConfig().translation.model),
+        ).toBe("gpt-6-luna");
     });
 });