diff --git a/extensions/anthropic-vertex/api.ts b/extensions/anthropic-vertex/api.ts
index 7b37892df88..dd62cafba68 100644
--- a/extensions/anthropic-vertex/api.ts
+++ b/extensions/anthropic-vertex/api.ts
@@ -17,6 +17,13 @@ export {
 import { buildAnthropicVertexProvider } from "./provider-catalog.js";
 import { hasAnthropicVertexAvailableAuth } from "./region.js";
 
+let streamRuntimeModulePromise: Promise<typeof import("./stream-runtime.js")> | null = null;
+
+const loadStreamRuntimeModule = async () => {
+  streamRuntimeModulePromise ??= import("./stream-runtime.js");
+  return await streamRuntimeModulePromise;
+};
+
 export function mergeImplicitAnthropicVertexProvider(params: {
   existing?: ReturnType<typeof buildAnthropicVertexProvider>;
   implicit: ReturnType<typeof buildAnthropicVertexProvider>;
@@ -50,7 +57,7 @@ export function createAnthropicVertexStreamFn(
   baseURL?: string,
   deps?: AnthropicVertexStreamDeps,
 ): StreamFn {
-  const streamFnPromise = import("./stream-runtime.js").then((runtime) =>
+  const streamFnPromise = loadStreamRuntimeModule().then((runtime) =>
     runtime.createAnthropicVertexStreamFn(projectId, region, baseURL, deps),
   );
   return async (model, context, options) => {
@@ -64,7 +71,7 @@ export function createAnthropicVertexStreamFnForModel(
   env: NodeJS.ProcessEnv = process.env,
   deps?: AnthropicVertexStreamDeps,
 ): StreamFn {
-  const streamFnPromise = import("./stream-runtime.js").then((runtime) =>
+  const streamFnPromise = loadStreamRuntimeModule().then((runtime) =>
     runtime.createAnthropicVertexStreamFnForModel(model, env, deps),
   );
   return async (...args) => {
diff --git a/extensions/codex/src/app-server/client-factory.ts b/extensions/codex/src/app-server/client-factory.ts
index 8b042d8d4bf..6da1f219ea6 100644
--- a/extensions/codex/src/app-server/client-factory.ts
+++ b/extensions/codex/src/app-server/client-factory.ts
@@ -13,13 +13,20 @@ export type CodexAppServerClientFactory = (
   config?: AuthProfileOrderConfig,
 ) => Promise<CodexAppServerClient>;
 
+let sharedClientModulePromise: Promise<typeof import("./shared-client.js")> | null = null;
+
+const loadSharedClientModule = async () => {
+  sharedClientModulePromise ??= import("./shared-client.js");
+  return await sharedClientModulePromise;
+};
+
 export const defaultCodexAppServerClientFactory: CodexAppServerClientFactory = (
   startOptions,
   authProfileId,
   agentDir,
   config,
 ) =>
-  import("./shared-client.js").then(({ getSharedCodexAppServerClient }) =>
+  loadSharedClientModule().then(({ getSharedCodexAppServerClient }) =>
     getSharedCodexAppServerClient({ startOptions, authProfileId, agentDir, config }),
   );
 
@@ -29,6 +36,6 @@ export const defaultLeasedCodexAppServerClientFactory: CodexAppServerClientFacto
   agentDir,
   config,
 ) =>
-  import("./shared-client.js").then(({ getLeasedSharedCodexAppServerClient }) =>
+  loadSharedClientModule().then(({ getLeasedSharedCodexAppServerClient }) =>
     getLeasedSharedCodexAppServerClient({ startOptions, authProfileId, agentDir, config }),
   );