diff --git a/.changeset/lazy-firebase-admin.md b/.changeset/lazy-firebase-admin.md
new file mode 100644
index 00000000..7aca4f57
--- /dev/null
+++ b/.changeset/lazy-firebase-admin.md
@@ -0,0 +1,5 @@
+---
+"files-sdk": patch
+---
+
+Avoid loading Firebase Admin when the Firebase Storage adapter receives an initialized bucket.
diff --git a/packages/files-sdk/src/firebase-storage/firebase-admin-loader.ts b/packages/files-sdk/src/firebase-storage/firebase-admin-loader.ts
new file mode 100644
index 00000000..09a11eec
--- /dev/null
+++ b/packages/files-sdk/src/firebase-storage/firebase-admin-loader.ts
@@ -0,0 +1,28 @@
+import { createRequire } from "node:module";
+
+import type {
+  applicationDefault,
+  cert,
+  getApps,
+  initializeApp,
+} from "firebase-admin/app";
+import type { getStorage } from "firebase-admin/storage";
+
+const require = createRequire(import.meta.url);
+
+interface FirebaseAdminAppModule {
+  applicationDefault: typeof applicationDefault;
+  cert: typeof cert;
+  getApps: typeof getApps;
+  initializeApp: typeof initializeApp;
+}
+
+interface FirebaseAdminStorageModule {
+  getStorage: typeof getStorage;
+}
+
+export const loadFirebaseAdminApp = (): FirebaseAdminAppModule =>
+  require("firebase-admin/app") as FirebaseAdminAppModule;
+
+export const loadFirebaseAdminStorage = (): FirebaseAdminStorageModule =>
+  require("firebase-admin/storage") as FirebaseAdminStorageModule;
diff --git a/packages/files-sdk/src/firebase-storage/index.ts b/packages/files-sdk/src/firebase-storage/index.ts
index 7faf16c5..41a0e78f 100644
--- a/packages/files-sdk/src/firebase-storage/index.ts
+++ b/packages/files-sdk/src/firebase-storage/index.ts
@@ -9,13 +9,6 @@ import type {
   GenerateSignedPostPolicyV4Options,
 } from "@google-cloud/storage";
 import type { App } from "firebase-admin/app";
-import {
-  applicationDefault,
-  cert,
-  getApps,
-  initializeApp,
-} from "firebase-admin/app";
-import { getStorage } from "firebase-admin/storage";
 
 import type {
   Adapter,
@@ -38,6 +31,10 @@ import { readEnv } from "../internal/env.js";
 import { FilesError } from "../internal/errors.js";
 import { createGcsResumableDriver } from "../internal/gcs-resumable.js";
 import { createStoredFile } from "../internal/stored-file.js";
+import {
+  loadFirebaseAdminApp,
+  loadFirebaseAdminStorage,
+} from "./firebase-admin-loader.js";
 
 export interface FirebaseStorageAdapterOptions {
   /**
@@ -231,10 +228,12 @@ const resolveBucketName = (
 // it as ours to keep the adapter's types consistent regardless of which copy
 // each dependency resolves to. Without this, the build's tsc fails on Linux CI
 // where the two copies diverge (7.19 vs 7.21) even though it passes on macOS.
-const adminBucket = (app: App, name?: string): Bucket =>
-  (name
+const adminBucket = (app: App, name?: string): Bucket => {
+  const { getStorage } = loadFirebaseAdminStorage();
+  return (name
     ? getStorage(app).bucket(name)
     : getStorage(app).bucket()) as unknown as Bucket;
+};
 
 const buildBucket = (opts: FirebaseStorageAdapterOptions): Bucket => {
   if (opts.app) {
@@ -278,6 +277,8 @@ const buildBucket = (opts: FirebaseStorageAdapterOptions): Bucket => {
   const appName =
     opts.appName ?? `files-sdk:${projectId ?? "default"}:${storageBucket}`;
 
+  const { applicationDefault, cert, getApps, initializeApp } =
+    loadFirebaseAdminApp();
   const existing = getApps().find((a) => a.name === appName);
   const app =
     existing ??
diff --git a/packages/files-sdk/test/build-output.test.ts b/packages/files-sdk/test/build-output.test.ts
index 92104afb..85568c61 100644
--- a/packages/files-sdk/test/build-output.test.ts
+++ b/packages/files-sdk/test/build-output.test.ts
@@ -146,6 +146,22 @@ test(
   COLD_BUILD_TIMEOUT_MS
 );
 
+// The firebase-storage entry reaches `firebase-admin` only through the
+// `createRequire` loader — invisible to bundlers — so an injected `Bucket`
+// works without the peer being resolvable. Guard against a top-level
+// `firebase-admin` import creeping back into the graph.
+test(
+  "firebase-storage bundle never statically imports an optional peer, even across dynamic chunks",
+  () => {
+    ensureBuilt();
+    const firebaseBundle = path.resolve(distDir, "firebase-storage/index.js");
+    expect(
+      offendingOptionalPeers(firebaseBundle, { followDynamic: true })
+    ).toEqual([]);
+  },
+  COLD_BUILD_TIMEOUT_MS
+);
+
 test(
   "react bundle is a `use client` module importing only react",
   () => {
diff --git a/packages/files-sdk/test/firebase-storage.test.ts b/packages/files-sdk/test/firebase-storage.test.ts
index e6e719ea..ae411bc5 100644
--- a/packages/files-sdk/test/firebase-storage.test.ts
+++ b/packages/files-sdk/test/firebase-storage.test.ts
@@ -109,7 +109,7 @@ const certMock = mock(
 );
 const applicationDefaultMock = mock(() => ({ _kind: "adc" }));
 
-mock.module("firebase-admin/app", () => ({
+const loadFirebaseAdminAppMock = mock(() => ({
   applicationDefault: applicationDefaultMock,
   cert: certMock,
   getApp: getAppMock,
@@ -121,10 +121,15 @@ const getStorageMock = mock((_app?: FakeApp) => ({
   bucket: (_name?: string) => fakeBucket,
 }));
 
-mock.module("firebase-admin/storage", () => ({
+const loadFirebaseAdminStorageMock = mock(() => ({
   getStorage: getStorageMock,
 }));
 
+mock.module("../src/firebase-storage/firebase-admin-loader.js", () => ({
+  loadFirebaseAdminApp: loadFirebaseAdminAppMock,
+  loadFirebaseAdminStorage: loadFirebaseAdminStorageMock,
+}));
+
 const { firebaseStorage, mapFirebaseStorageError } =
   await import("../src/firebase-storage/index.js");
 
@@ -153,6 +158,8 @@ beforeEach(() => {
   certMock.mockClear();
   applicationDefaultMock.mockClear();
   getStorageMock.mockClear();
+  loadFirebaseAdminAppMock.mockClear();
+  loadFirebaseAdminStorageMock.mockClear();
   initializedApps.length = 0;
 
   saveMock.mockImplementation(async () => {});
@@ -204,6 +211,16 @@ beforeEach(() => {
 });
 
 describe("firebase-storage adapter", () => {
+  test("does not load firebase-admin for an injected Bucket", () => {
+    firebaseStorage({
+      app: fakeBucket as unknown as NonNullable<
+        Parameters<typeof firebaseStorage>[0]
+      >["app"],
+    });
+    expect(loadFirebaseAdminAppMock).not.toHaveBeenCalled();
+    expect(loadFirebaseAdminStorageMock).not.toHaveBeenCalled();
+  });
+
   test("missing bucket and projectId throws at construction", () => {
     expect(() => firebaseStorage()).toThrow(/bucket/u);
   });