Generate content using Vertex AI Express Mode

This sample utilizes Vertex AI Express Mode to generate text content.

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For detailed documentation that includes this code sample, see the following:

Code sample

Go

Before trying this sample, follow the Go setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI Go API reference documentation.

To authenticate to Vertex AI, set up Application Default Credentials. For more information, see Set up authentication for a local development environment. 

import (
	"context"
	"fmt"
	"io"

	"google.golang.org/genai"
)

var newClient = genai.NewClient

// generateContent shows how to use Vertex AI Express mode with an API key.
func generateContentWithApiKey(w io.Writer) error {
	ctx := context.Background()

	// TODO(developer): Replace with your actual API key
	apiKey := "YOUR_API_KEY"

	client, err := newClient(ctx, &genai.ClientConfig{
		APIKey:      apiKey,
		HTTPOptions: genai.HTTPOptions{APIVersion: "v1"},
	})
	if err != nil {
		return fmt.Errorf("failed to create genai client: %w", err)
	}

	modelName := "gemini-2.5-flash"
	resp, err := client.Models.GenerateContent(ctx, modelName,
		[]*genai.Content{
			{Parts: []*genai.Part{
				{Text: "Explain bubble sort to me."},
			}, Role: genai.RoleUser},
		},
		nil,
	)
	if err != nil {
		return fmt.Errorf("failed to generate content: %w", err)
	}

	fmt.Fprintln(w, resp.Text())

	// Example response:
	// Bubble Sort is a simple sorting algorithm that repeatedly steps through the list

	return nil
}

Java

Before trying this sample, follow the Java setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI Java API reference documentation.

To authenticate to Vertex AI, set up Application Default Credentials. For more information, see Set up authentication for a local development environment. 


import com.google.genai.Client;
import com.google.genai.types.GenerateContentConfig;
import com.google.genai.types.GenerateContentResponse;

public class ExpressModeWithApiKey {

  public static void main(String[] args) {
    // TODO(developer): Replace these variables before running the sample.
    String modelId = "gemini-2.5-flash";
    String apiKey = "YOUR_API_KEY";
    generateContent(modelId, apiKey);
  }

  // Generates content with Vertex AI Api key.
  public static String generateContent(String modelId, String apiKey) {
    // Client Initialization. Once created, it can be reused for multiple requests.
    try (Client client = Client.builder().apiKey(apiKey).vertexAI(true).build()) {

      GenerateContentResponse response =
          client.models.generateContent(
              modelId, "Explain bubble sort to me.", GenerateContentConfig.builder().build());

      System.out.print(response.text());
      // Example response:
      // Bubble sort is one of the simplest sorting algorithms. It's often used to introduce the
      // concept of sorting because its logic is very straightforward.
      //
      // Imagine you have a list of numbers that you want to put in order, like `[5, 1, 4, 2, 8]`.
      // ...
      return response.text();
    }
  }
}

Node.js

Before trying this sample, follow the Node.js setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI Node.js API reference documentation.

To authenticate to Vertex AI, set up Application Default Credentials. For more information, see Set up authentication for a local development environment. 

const {GoogleGenAI} = require('@google/genai');
const API_KEY = 'YOUR_EXPRESS_MODE_API_KEY';

async function generateWithApiKey(apiKey = API_KEY) {
  const client = new GoogleGenAI({
    vertexai: true,
    apiKey: apiKey,
  });

  const response = await client.models.generateContentStream({
    model: 'gemini-2.5-flash',
    contents: 'Explain bubble sort to me.',
  });

  console.log(response.text);

  // Example response:
  //  Bubble Sort is a simple sorting algorithm that repeatedly steps through the list

  return response;
}

Python

Before trying this sample, follow the Python setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI Python API reference documentation.

To authenticate to Vertex AI, set up Application Default Credentials. For more information, see Set up authentication for a local development environment. 

from google import genai

# TODO(developer): Update below line
API_KEY = "YOUR_API_KEY"

client = genai.Client(vertexai=True, api_key=API_KEY)

response = client.models.generate_content(
    model="gemini-2.5-flash",
    contents="Explain bubble sort to me.",
)

print(response.text)
# Example response:
# Bubble Sort is a simple sorting algorithm that repeatedly steps through the list

What's next

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