[v5]: Adds Google/VertexAI reasoning messages

.changeset/khaki-poets-remember.md

@@ -0,0 +1,6 @@
+---
+'@ai-sdk/google-vertex': patch
+'@ai-sdk/google': patch
+---
+
+Adds support for Gemini/Vertex thinking messages

content/providers/01-ai-sdk-providers/16-google-vertex.mdx

@@ -326,6 +326,72 @@ const { text } = await generateText({
 Google Vertex language models can also be used in the `streamText` function
 (see [AI SDK Core](/docs/ai-sdk-core)).
 
+#### Reasoning (Thinking Tokens)
+
+Google Vertex AI, through its support for Gemini models, can also emit "thinking" tokens, representing the model's reasoning process. The AI SDK exposes these as reasoning information.
+
+To enable thinking tokens for compatible Gemini models via Vertex, set `includeThoughts: true` in the `thinkingConfig` provider option. Since the Vertex provider uses the Google provider's underlying language model, these options are passed through `providerOptions.google`:
+
+```ts
+import { vertex } from '@ai-sdk/google-vertex';
+import { GoogleGenerativeAIProviderOptions } from '@ai-sdk/google'; // Note: importing from @ai-sdk/google
+import { generateText, streamText } from 'ai';
+
+// For generateText:
+const { content } = await generateText({
+  model: vertex('gemini-2.5-flash-preview-04-17'), // Or other supported model via Vertex
+  providerOptions: {
+    google: {
+      // Options are nested under 'google' for Vertex provider
+      thinkingConfig: {
+        includeThoughts: true,
+        // thinkingBudget: 2048, // Optional
+      },
+    } satisfies GoogleGenerativeAIProviderOptions,
+  },
+  prompt: 'Explain quantum computing in simple terms.',
+});
+
+for (const part of content) {
+  if (part.type === 'text') {
+    process.stdout.write(part.text);
+  } else if (part.type === 'reasoning') {
+    process.stdout.write(`THOUGHT: ${part.text}\n`);
+  }
+}
+
+// For streamText:
+const result = streamText({
+  model: vertex('gemini-2.5-flash-preview-04-17'), // Or other supported model via Vertex
+  providerOptions: {
+    google: {
+      // Options are nested under 'google' for Vertex provider
+      thinkingConfig: {
+        includeThoughts: true,
+        // thinkingBudget: 2048, // Optional
+      },
+    } satisfies GoogleGenerativeAIProviderOptions,
+  },
+  prompt: 'Explain quantum computing in simple terms.',
+});
+
+for await (const part of result.fullStream) {
+  if (part.type === 'reasoning') {
+    process.stdout.write(`THOUGHT: ${part.text}\n`);
+  } else if (part.type === 'text') {
+    process.stdout.write(part.text);
+  }
+}
+```
+
+When `includeThoughts` is true, parts of the API response marked with `thought: true` will be processed as reasoning.
+
+<Note>
+  Refer to the [Google Vertex AI documentation on
+  "thinking"](https://cloud.google.com/vertex-ai/generative-ai/docs/thinking)
+  for model compatibility and further details.
+</Note>
+
 #### File Inputs
 
 The Google Vertex provider supports file inputs, e.g. PDF files.

examples/ai-core/src/generate-text/google-vertex-reasoning-generate-text.ts

@@ -0,0 +1,28 @@
+import { vertex } from '@ai-sdk/google-vertex';
+import { generateText } from 'ai';
+
+async function main() {
+  const { content } = await generateText({
+    model: vertex('gemini-2.5-flash-preview-04-17'),
+    prompt:
+      "Describe the most unusual or striking architectural feature you've ever seen in a building or structure.",
+    providerOptions: {
+      google: {
+        thinkingConfig: {
+          thinkingBudget: 2048,
+          includeThoughts: true,
+        },
+      },
+    },
+  });
+
+  for (const part of content) {
+    if (part.type === 'text') {
+      process.stdout.write(part.text);
+    } else if (part.type === 'reasoning') {
+      process.stdout.write('\x1b[34m' + part.text + '\x1b[0m');
+    }
+  }
+}
+
+main().catch(console.log);

examples/ai-core/src/generate-text/google-vertex-reasoning.ts

@@ -0,0 +1,35 @@
+import { vertex } from '@ai-sdk/google-vertex';
+import { streamText } from 'ai';
+
+async function main() {
+  const result = streamText({
+    model: vertex('gemini-2.5-flash-preview-04-17'),
+    prompt:
+      "Describe the most unusual or striking architectural feature you've ever seen in a building or structure.",
+    providerOptions: {
+      google: {
+        thinkingConfig: {
+          thinkingBudget: 2048,
+          includeThoughts: true,
+        },
+      },
+    },
+  });
+
+  for await (const part of result.fullStream) {
+    if (part.type === 'reasoning') {
+      process.stdout.write('\x1b[34m' + part.text + '\x1b[0m');
+    } else if (part.type === 'text') {
+      process.stdout.write(part.text);
+    }
+  }
+
+  console.log();
+  console.log('Warnings:', await result.warnings);
+
+  console.log();
+  console.log('Token usage:', await result.usage);
+  console.log('Finish reason:', await result.finishReason);
+}
+
+main().catch(console.log);