diff --git a/packages/ai/src/providers/google-vertex-messages.ts b/packages/ai/src/providers/google-vertex-messages.ts
index 53c4e16b0d0..9dbbc441a1c 100644
--- a/packages/ai/src/providers/google-vertex-messages.ts
+++ b/packages/ai/src/providers/google-vertex-messages.ts
@@ -91,7 +91,7 @@ export const configure = (input: Config = {}) => {
   const route = configuredRoute(input)
   return {
     id,
-    model: (modelID: string | ModelID) => route.model({ id: modelID }),
+    model: (modelID: string | ModelID) => route.model<AnthropicMessages.ProviderOptionsInput>({ id: modelID }),
     configure,
   }
 }
@@ -101,7 +101,10 @@ export const provider = {
   configure,
 }
 
-export const model: ProviderPackage.Definition<Settings>["model"] = (modelID, settings) => {
+export const model: ProviderPackage.Definition<Settings, AnthropicMessages.ProviderOptionsInput>["model"] = (
+  modelID,
+  settings,
+) => {
   if (settings.apiKey !== undefined) throw new Error("Google Vertex Messages does not support API keys")
   return configure({
     accessToken: settings.accessToken,
diff --git a/packages/ai/test/provider-options/google-vertex-messages.types.ts b/packages/ai/test/provider-options/google-vertex-messages.types.ts
new file mode 100644
index 00000000000..040a4e03da3
--- /dev/null
+++ b/packages/ai/test/provider-options/google-vertex-messages.types.ts
@@ -0,0 +1,13 @@
+import { LLM } from "../../src"
+import { GoogleVertexMessages } from "../../src/providers"
+
+const model = GoogleVertexMessages.configure({ accessToken: "test", project: "project" }).model("claude")
+
+LLM.request({ model, prompt: "Hello", providerOptions: { anthropic: { effort: "medium" } } })
+
+LLM.request({
+  model,
+  prompt: "Hello",
+  // @ts-expect-error Vertex Anthropic effort must be a string.
+  providerOptions: { anthropic: { effort: false } },
+})