diff --git a/src/extension-host/runtime-backend-catalog.test.ts b/src/extension-host/runtime-backend-catalog.test.ts
index c6e6438e17e..c30671e6ed6 100644
--- a/src/extension-host/runtime-backend-catalog.test.ts
+++ b/src/extension-host/runtime-backend-catalog.test.ts
@@ -36,8 +36,8 @@ vi.mock("./media-runtime-registry.js", () => ({
   ),
 }));
 
-vi.mock("./tts-runtime-registry.js", () => ({
-  listExtensionHostTtsRuntimeProviders: vi.fn(() => [
+vi.mock("./tts-runtime-backends.js", () => ({
+  listExtensionHostTtsRuntimeBackends: vi.fn(() => [
     { id: "openai", supportsTelephony: true },
     { id: "elevenlabs", supportsTelephony: true },
     { id: "edge", supportsTelephony: false },
diff --git a/src/extension-host/runtime-backend-catalog.ts b/src/extension-host/runtime-backend-catalog.ts
index 46e6ccd16df..6de91699e38 100644
--- a/src/extension-host/runtime-backend-catalog.ts
+++ b/src/extension-host/runtime-backend-catalog.ts
@@ -13,7 +13,7 @@ import {
   buildExtensionHostMediaUnderstandingRegistry,
   normalizeExtensionHostMediaProviderId,
 } from "./media-runtime-registry.js";
-import { listExtensionHostTtsRuntimeProviders } from "./tts-runtime-registry.js";
+import { listExtensionHostTtsRuntimeBackends } from "./tts-runtime-backends.js";
 
 export const EXTENSION_HOST_RUNTIME_BACKEND_FAMILY = "capability.runtime-backend";
 
@@ -203,7 +203,7 @@ export function resolveExtensionHostMediaRuntimeDefaultModel(params: {
 }
 
 export function listExtensionHostTtsRuntimeBackendCatalogEntries(): readonly ExtensionHostRuntimeBackendCatalogEntry[] {
-  return listExtensionHostTtsRuntimeProviders().map((provider, defaultRank) => ({
+  return listExtensionHostTtsRuntimeBackends().map((provider, defaultRank) => ({
     id: buildRuntimeBackendCatalogId("tts", provider.id),
     family: EXTENSION_HOST_RUNTIME_BACKEND_FAMILY,
     subsystemId: "tts",
diff --git a/src/extension-host/tts-runtime-backends.test.ts b/src/extension-host/tts-runtime-backends.test.ts
new file mode 100644
index 00000000000..5f5aea6be60
--- /dev/null
+++ b/src/extension-host/tts-runtime-backends.test.ts
@@ -0,0 +1,37 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import {
+  EXTENSION_HOST_TTS_RUNTIME_BACKEND_IDS,
+  getExtensionHostTtsRuntimeBackend,
+  listExtensionHostTtsRuntimeBackends,
+} from "./tts-runtime-backends.js";
+
+describe("tts-runtime-backends", () => {
+  afterEach(() => {
+    vi.unstubAllEnvs();
+  });
+
+  it("keeps the built-in backend order stable", () => {
+    expect(EXTENSION_HOST_TTS_RUNTIME_BACKEND_IDS).toEqual(["openai", "elevenlabs", "edge"]);
+    expect(listExtensionHostTtsRuntimeBackends().map((backend) => backend.id)).toEqual([
+      "openai",
+      "elevenlabs",
+      "edge",
+    ]);
+  });
+
+  it("resolves API keys and configuration through shared backend definitions", () => {
+    vi.stubEnv("OPENAI_API_KEY", "");
+    vi.stubEnv("ELEVENLABS_API_KEY", "");
+    vi.stubEnv("XI_API_KEY", "");
+
+    const config = {
+      openai: { apiKey: "openai-key" },
+      elevenlabs: { apiKey: "" },
+      edge: { enabled: true },
+    } as const;
+
+    expect(getExtensionHostTtsRuntimeBackend("openai")?.resolveApiKey(config)).toBe("openai-key");
+    expect(getExtensionHostTtsRuntimeBackend("elevenlabs")?.isConfigured(config)).toBe(false);
+    expect(getExtensionHostTtsRuntimeBackend("edge")?.supportsTelephony).toBe(false);
+  });
+});
diff --git a/src/extension-host/tts-runtime-backends.ts b/src/extension-host/tts-runtime-backends.ts
new file mode 100644
index 00000000000..eeaad8133ec
--- /dev/null
+++ b/src/extension-host/tts-runtime-backends.ts
@@ -0,0 +1,56 @@
+import type { TtsProvider } from "../config/types.tts.js";
+import type { ResolvedTtsConfig } from "./tts-config.js";
+
+export type ExtensionHostTtsRuntimeBackend = {
+  id: TtsProvider;
+  supportsTelephony: boolean;
+  resolveApiKey: (config: ResolvedTtsConfig) => string | undefined;
+  isConfigured: (config: ResolvedTtsConfig) => boolean;
+};
+
+const EXTENSION_HOST_TTS_RUNTIME_BACKENDS: readonly ExtensionHostTtsRuntimeBackend[] = [
+  {
+    id: "openai",
+    supportsTelephony: true,
+    resolveApiKey(config) {
+      return config.openai.apiKey || process.env.OPENAI_API_KEY;
+    },
+    isConfigured(config) {
+      return Boolean(this.resolveApiKey(config));
+    },
+  },
+  {
+    id: "elevenlabs",
+    supportsTelephony: true,
+    resolveApiKey(config) {
+      return config.elevenlabs.apiKey || process.env.ELEVENLABS_API_KEY || process.env.XI_API_KEY;
+    },
+    isConfigured(config) {
+      return Boolean(this.resolveApiKey(config));
+    },
+  },
+  {
+    id: "edge",
+    supportsTelephony: false,
+    resolveApiKey() {
+      return undefined;
+    },
+    isConfigured(config) {
+      return config.edge.enabled;
+    },
+  },
+] as const;
+
+export const EXTENSION_HOST_TTS_RUNTIME_BACKEND_IDS = EXTENSION_HOST_TTS_RUNTIME_BACKENDS.map(
+  (backend) => backend.id,
+) as readonly TtsProvider[];
+
+export function listExtensionHostTtsRuntimeBackends(): readonly ExtensionHostTtsRuntimeBackend[] {
+  return EXTENSION_HOST_TTS_RUNTIME_BACKENDS;
+}
+
+export function getExtensionHostTtsRuntimeBackend(
+  id: TtsProvider,
+): ExtensionHostTtsRuntimeBackend | undefined {
+  return EXTENSION_HOST_TTS_RUNTIME_BACKENDS.find((backend) => backend.id === id);
+}
diff --git a/src/extension-host/tts-runtime-registry.ts b/src/extension-host/tts-runtime-registry.ts
index 331b97cebbe..7af49fcc99e 100644
--- a/src/extension-host/tts-runtime-registry.ts
+++ b/src/extension-host/tts-runtime-registry.ts
@@ -1,58 +1,24 @@
 import type { TtsProvider } from "../config/types.tts.js";
 import type { ResolvedTtsConfig } from "./tts-config.js";
+import {
+  EXTENSION_HOST_TTS_RUNTIME_BACKEND_IDS,
+  getExtensionHostTtsRuntimeBackend,
+  listExtensionHostTtsRuntimeBackends,
+  type ExtensionHostTtsRuntimeBackend,
+} from "./tts-runtime-backends.js";
 
-export type ExtensionHostTtsRuntimeProvider = {
-  id: TtsProvider;
-  supportsTelephony: boolean;
-  resolveApiKey: (config: ResolvedTtsConfig) => string | undefined;
-  isConfigured: (config: ResolvedTtsConfig) => boolean;
-};
+export type ExtensionHostTtsRuntimeProvider = ExtensionHostTtsRuntimeBackend;
 
-const EXTENSION_HOST_TTS_RUNTIME_PROVIDERS: readonly ExtensionHostTtsRuntimeProvider[] = [
-  {
-    id: "openai",
-    supportsTelephony: true,
-    resolveApiKey(config) {
-      return config.openai.apiKey || process.env.OPENAI_API_KEY;
-    },
-    isConfigured(config) {
-      return Boolean(this.resolveApiKey(config));
-    },
-  },
-  {
-    id: "elevenlabs",
-    supportsTelephony: true,
-    resolveApiKey(config) {
-      return config.elevenlabs.apiKey || process.env.ELEVENLABS_API_KEY || process.env.XI_API_KEY;
-    },
-    isConfigured(config) {
-      return Boolean(this.resolveApiKey(config));
-    },
-  },
-  {
-    id: "edge",
-    supportsTelephony: false,
-    resolveApiKey() {
-      return undefined;
-    },
-    isConfigured(config) {
-      return config.edge.enabled;
-    },
-  },
-] as const;
-
-export const EXTENSION_HOST_TTS_PROVIDER_IDS = EXTENSION_HOST_TTS_RUNTIME_PROVIDERS.map(
-  (provider) => provider.id,
-) as readonly TtsProvider[];
+export const EXTENSION_HOST_TTS_PROVIDER_IDS = EXTENSION_HOST_TTS_RUNTIME_BACKEND_IDS;
 
 export function listExtensionHostTtsRuntimeProviders(): readonly ExtensionHostTtsRuntimeProvider[] {
-  return EXTENSION_HOST_TTS_RUNTIME_PROVIDERS;
+  return listExtensionHostTtsRuntimeBackends();
 }
 
 export function getExtensionHostTtsRuntimeProvider(
   id: TtsProvider,
 ): ExtensionHostTtsRuntimeProvider | undefined {
-  return EXTENSION_HOST_TTS_RUNTIME_PROVIDERS.find((provider) => provider.id === id);
+  return getExtensionHostTtsRuntimeBackend(id);
 }
 
 export function resolveExtensionHostTtsApiKey(