diff --git a/.changeset/rare-hats-know.md b/.changeset/rare-hats-know.md
new file mode 100644
index 00000000000..68fafc7849d
--- /dev/null
+++ b/.changeset/rare-hats-know.md
@@ -0,0 +1,5 @@
+---
+'@firebase/ai': patch
+---
+
+Fix logic for merging default `onDeviceParams` with user-provided `onDeviceParams`.
diff --git a/packages/ai/src/methods/chrome-adapter-browser.test.ts b/packages/ai/src/methods/chrome-adapter-browser.test.ts
index 5d5b2344ab6..e37a08bf1a9 100644
--- a/packages/ai/src/methods/chrome-adapter-browser.test.ts
+++ b/packages/ai/src/methods/chrome-adapter-browser.test.ts
@@ -78,6 +78,63 @@ describe('ChromeAdapter', () => {
         expectedInputs: [{ type: 'image' }]
       });
     });
+    it('sets image as expected input type by default even if other onDeviceParams params are set', async () => {
+      const languageModelProvider = {
+        availability: () => Promise.resolve(Availability.AVAILABLE)
+      } as LanguageModel;
+      const availabilityStub = stub(
+        languageModelProvider,
+        'availability'
+      ).resolves(Availability.AVAILABLE);
+      const adapter = new ChromeAdapterImpl(
+        languageModelProvider,
+        InferenceMode.PREFER_ON_DEVICE,
+        {
+          promptOptions: {}
+        }
+      );
+      await adapter.isAvailable({
+        contents: [
+          {
+            role: 'user',
+            parts: [{ text: 'hi' }]
+          }
+        ]
+      });
+      expect(availabilityStub).to.have.been.calledWith({
+        expectedInputs: [{ type: 'image' }]
+      });
+    });
+    it('sets image as expected input type by default even if other createOptions params are set', async () => {
+      const languageModelProvider = {
+        availability: () => Promise.resolve(Availability.AVAILABLE)
+      } as LanguageModel;
+      const availabilityStub = stub(
+        languageModelProvider,
+        'availability'
+      ).resolves(Availability.AVAILABLE);
+      const adapter = new ChromeAdapterImpl(
+        languageModelProvider,
+        InferenceMode.PREFER_ON_DEVICE,
+        {
+          createOptions: {
+            topK: 22
+          }
+        }
+      );
+      await adapter.isAvailable({
+        contents: [
+          {
+            role: 'user',
+            parts: [{ text: 'hi' }]
+          }
+        ]
+      });
+      expect(availabilityStub).to.have.been.calledWith({
+        topK: 22,
+        expectedInputs: [{ type: 'image' }]
+      });
+    });
     it('honors explicitly set expected inputs', async () => {
       const languageModelProvider = {
         availability: () => Promise.resolve(Availability.AVAILABLE)
diff --git a/packages/ai/src/methods/chrome-adapter.ts b/packages/ai/src/methods/chrome-adapter.ts
index a0ab509e335..839276814bb 100644
--- a/packages/ai/src/methods/chrome-adapter.ts
+++ b/packages/ai/src/methods/chrome-adapter.ts
@@ -31,11 +31,15 @@ import { ChromeAdapter } from '../types/chrome-adapter';
 import {
   Availability,
   LanguageModel,
+  LanguageModelExpected,
   LanguageModelMessage,
   LanguageModelMessageContent,
   LanguageModelMessageRole
 } from '../types/language-model';
 
+// Defaults to support image inputs for convenience.
+const defaultExpectedInputs: LanguageModelExpected[] = [{ type: 'image' }];
+
 /**
  * Defines an inference "backend" that uses Chrome's on-device model,
  * and encapsulates logic for detecting when on-device inference is
@@ -47,16 +51,28 @@ export class ChromeAdapterImpl implements ChromeAdapter {
   private isDownloading = false;
   private downloadPromise: Promise<LanguageModel | void> | undefined;
   private oldSession: LanguageModel | undefined;
+  onDeviceParams: OnDeviceParams = {
+    createOptions: {
+      expectedInputs: defaultExpectedInputs
+    }
+  };
   constructor(
     public languageModelProvider: LanguageModel,
     public mode: InferenceMode,
-    public onDeviceParams: OnDeviceParams = {
-      createOptions: {
-        // Defaults to support image inputs for convenience.
-        expectedInputs: [{ type: 'image' }]
+    onDeviceParams?: OnDeviceParams
+  ) {
+    if (onDeviceParams) {
+      this.onDeviceParams = onDeviceParams;
+      if (!this.onDeviceParams.createOptions) {
+        this.onDeviceParams.createOptions = {
+          expectedInputs: defaultExpectedInputs
+        };
+      } else if (!this.onDeviceParams.createOptions.expectedInputs) {
+        this.onDeviceParams.createOptions.expectedInputs =
+          defaultExpectedInputs;
       }
     }
-  ) {}
+  }
 
   /**
    * Checks if a given request can be made on-device.