Gemini API in Vertex AI quickstart

This quickstart shows you how to install the Google Gen AI SDK for your language of choice and then make your first API request. It covers the following topics:

• Install the SDK and set up your environment: Set up your development environment for Python, Go, Node.js, Java, or REST.
• Make your first request: Use the generateContent method to send a text prompt and receive a response.
• Generate images: Create an image from a descriptive text prompt.
• Image understanding: Provide an image as input to the model and ask questions about it.
• Code execution: Enable the model to generate and run Python code to solve problems.

Authentication Method	Description	Use Case
API key	A simple encrypted string that you can use to call the Gemini API in Vertex AI.	Best for quick prototyping and development when you don't need to access Google Cloud resources.
Application Default Credentials (ADC)	A strategy that finds credentials automatically based on the application environment, without needing to modify application code.	Recommended for most production applications, especially those running on Google Cloud, as it provides more robust and secure authentication.

Choose your authentication method:

API key ADC

---

Before you begin

Concepts

• API key: A simple encrypted string that identifies your project when calling the API, suitable for quick prototyping.
• Application Default Credentials (ADC): A method that automatically finds and uses service account credentials in a Google Cloud environment, recommended for production applications.

Prerequisites

Configure application default credentials if you haven't yet.

The following diagram summarizes the overall workflow:

Install the SDK and set up your environment

On your local machine, click one of the following tabs to install the SDK for your programming language.

Gen AI SDK for Python

Install and update the Gen AI SDK for Python by running this command.

pip install --upgrade google-genai

Set environment variables:

  # Replace the `GOOGLE_CLOUD_PROJECT` and `GOOGLE_CLOUD_LOCATION` values
  # with appropriate values for your project.
  export GOOGLE_CLOUD_PROJECT=GOOGLE_CLOUD_PROJECT
  export GOOGLE_CLOUD_LOCATION=global
export GOOGLE_GENAI_USE_VERTEXAI=True
  

Gen AI SDK for Go

Install and update the Gen AI SDK for Go by running this command.

go get google.golang.org/genai

Set environment variables:

  # Replace the `GOOGLE_CLOUD_PROJECT` and `GOOGLE_CLOUD_LOCATION` values
  # with appropriate values for your project.
  export GOOGLE_CLOUD_PROJECT=GOOGLE_CLOUD_PROJECT
  export GOOGLE_CLOUD_LOCATION=global
export GOOGLE_GENAI_USE_VERTEXAI=True
  

Gen AI SDK for Node.js

Install and update the Gen AI SDK for Node.js by running this command.

npm install @google/genai

Set environment variables:

  # Replace the `GOOGLE_CLOUD_PROJECT` and `GOOGLE_CLOUD_LOCATION` values
  # with appropriate values for your project.
  export GOOGLE_CLOUD_PROJECT=GOOGLE_CLOUD_PROJECT
  export GOOGLE_CLOUD_LOCATION=global
export GOOGLE_GENAI_USE_VERTEXAI=True
  

Gen AI SDK for Java

To install the Gen AI SDK for Java, add the following dependency to your Maven pom.xml file:

<dependencies>
  <dependency>
    <groupId>com.google.genai</groupId>
    <artifactId>google-genai</artifactId>
    <version>0.7.0</version>
  </dependency>
</dependencies>
  

Set environment variables:

  # Replace the `GOOGLE_CLOUD_PROJECT` and `GOOGLE_CLOUD_LOCATION` values
  # with appropriate values for your project.
  export GOOGLE_CLOUD_PROJECT=GOOGLE_CLOUD_PROJECT
  export GOOGLE_CLOUD_LOCATION=global
export GOOGLE_GENAI_USE_VERTEXAI=True
  

REST

Set environment variables:

  GOOGLE_CLOUD_PROJECT=GOOGLE_CLOUD_PROJECT
  GOOGLE_CLOUD_LOCATION=global
  API_ENDPOINT=YOUR_API_ENDPOINT
  MODEL_ID="gemini-2.5-flash"
  GENERATE_CONTENT_API="generateContent"
  

Make your first request

Use the generateContent method to send a request to the Gemini API in Vertex AI:

Python

from google import genai
from google.genai.types import HttpOptions

client = genai.Client(http_options=HttpOptions(api_version="v1"))
response = client.models.generate_content(
    model="gemini-2.5-flash",
    contents="How does AI work?",
)
print(response.text)
# Example response:
# Okay, let's break down how AI works. It's a broad field, so I'll focus on the ...
#
# Here's a simplified overview:
# ...

Go

import (
	"context"
	"fmt"
	"io"

	"google.golang.org/genai"
)

// generateWithText shows how to generate text using a text prompt.
func generateWithText(w io.Writer) error {
	ctx := context.Background()

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

	resp, err := client.Models.GenerateContent(ctx,
		"gemini-2.5-flash",
		genai.Text("How does AI work?"),
		nil,
	)
	if err != nil {
		return fmt.Errorf("failed to generate content: %w", err)
	}

	respText := resp.Text()

	fmt.Fprintln(w, respText)
	// Example response:
	// That's a great question! Understanding how AI works can feel like ...
	// ...
	// **1. The Foundation: Data and Algorithms**
	// ...

	return nil
}

Node.js

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

const GOOGLE_CLOUD_PROJECT = process.env.GOOGLE_CLOUD_PROJECT;
const GOOGLE_CLOUD_LOCATION = process.env.GOOGLE_CLOUD_LOCATION || 'global';

async function generateContent(
  projectId = GOOGLE_CLOUD_PROJECT,
  location = GOOGLE_CLOUD_LOCATION
) {
  const ai = new GoogleGenAI({
    vertexai: true,
    project: projectId,
    location: location,
  });

  const response = await ai.models.generateContent({
    model: 'gemini-2.5-flash',
    contents: 'How does AI work?',
  });

  console.log(response.text);

  return response.text;
}

Java

import com.google.genai.Client;
import com.google.genai.types.Content;
import com.google.genai.types.GenerateContentResponse;
import com.google.genai.types.HttpOptions;
import com.google.genai.types.Part;

public class TextGenerationWithText {

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

  // Generates text with text input
  public static String generateContent(String modelId) {
    // Initialize client that will be used to send requests. This client only needs to be created
    // once, and can be reused for multiple requests.
    try (Client client =
        Client.builder()
            .location("global")
            .vertexAI(true)
            .httpOptions(HttpOptions.builder().apiVersion("v1").build())
            .build()) {

      GenerateContentResponse response =
          client.models.generateContent(modelId, "How does AI work?", null);

      System.out.print(response.text());
      // Example response:
      // Okay, let's break down how AI works. It's a broad field, so I'll focus on the ...
      //
      // Here's a simplified overview:
      // ...
      return response.text();
    }
  }
}

REST

To send this prompt request, run the curl command from the command line or include the REST call in your application.

curl \
-X POST \
-H "Content-Type: application/json" \
-H "Authorization: Bearer $(gcloud auth print-access-token)" \
"https://${API_ENDPOINT}/v1/projects/${GOOGLE_CLOUD_PROJECT}/locations/${GOOGLE_CLOUD_LOCATION}/publishers/google/models/${MODEL_ID}:${GENERATE_CONTENT_API}" -d \
$'{
  "contents": {
    "role": "user",
    "parts": {
      "text": "Explain how AI works in a few words"
    }
  }
}'

The model returns a response. Note that the response is generated in sections with each section separately evaluated for safety.

Generate images

Gemini can generate and process images conversationally. You can prompt Gemini with text, images, or a combination of both to achieve various image-related tasks, such as image generation and editing. The following code demonstrates how to generate an image based on a descriptive prompt:

You must include responseModalities: ["TEXT", "IMAGE"] in your configuration. Image-only output is not supported with these models.

Python

from google import genai
from google.genai.types import GenerateContentConfig, Modality
from PIL import Image
from io import BytesIO

client = genai.Client()

response = client.models.generate_content(
    model="gemini-2.0-flash-preview-image-generation",
    contents=(
        "Generate an image of the Eiffel tower with fireworks in the background."
    ),
    config=GenerateContentConfig(response_modalities=[Modality.TEXT, Modality.IMAGE]),
)
for part in response.candidates[0].content.parts:
    if part.text:
        print(part.text)
    elif part.inline_data:
        image = Image.open(BytesIO((part.inline_data.data)))
        image.save("example-image.png")
# Example response:
#   A beautiful photograph captures the iconic Eiffel Tower in Paris, France,
#   against a backdrop of a vibrant and dynamic fireworks display. The tower itself...

Node.js

const fs = require('fs');
const {GoogleGenAI, Modality} = require('@google/genai');

const GOOGLE_CLOUD_PROJECT = process.env.GOOGLE_CLOUD_PROJECT;
const GOOGLE_CLOUD_LOCATION =
  process.env.GOOGLE_CLOUD_LOCATION || 'us-central1';

async function generateContent(
  projectId = GOOGLE_CLOUD_PROJECT,
  location = GOOGLE_CLOUD_LOCATION
) {
  const ai = new GoogleGenAI({
    vertexai: true,
    project: projectId,
    location: location,
  });

  const response = await ai.models.generateContentStream({
    model: 'gemini-2.0-flash-exp',
    contents:
      'Generate an image of the Eiffel tower with fireworks in the background.',
    config: {
      responseModalities: [Modality.TEXT, Modality.IMAGE],
    },
  });

  const generatedFileNames = [];
  let imageIndex = 0;
  for await (const chunk of response) {
    const text = chunk.text;
    const data = chunk.data;
    if (text) {
      console.debug(text);
    } else if (data) {
      const fileName = `generate_content_streaming_image_${imageIndex++}.png`;
      console.debug(`Writing response image to file: ${fileName}.`);
      try {
        fs.writeFileSync(fileName, data);
        generatedFileNames.push(fileName);
      } catch (error) {
        console.error(`Failed to write image file ${fileName}:`, error);
      }
    }
  }

  return generatedFileNames;
}

Image understanding

Gemini can understand images as well. The following code uses the image generated in the previous section and uses a different model to infer information about the image:

Python

from google import genai
from google.genai.types import HttpOptions, Part

client = genai.Client(http_options=HttpOptions(api_version="v1"))
response = client.models.generate_content(
    model="gemini-2.5-flash",
    contents=[
        "What is shown in this image?",
        Part.from_uri(
            file_uri="gs://cloud-samples-data/generative-ai/image/scones.jpg",
            mime_type="image/jpeg",
        ),
    ],
)
print(response.text)
# Example response:
# The image shows a flat lay of blueberry scones arranged on parchment paper. There are ...

Go

import (
	"context"
	"fmt"
	"io"

	genai "google.golang.org/genai"
)

// generateWithTextImage shows how to generate text using both text and image input
func generateWithTextImage(w io.Writer) error {
	ctx := context.Background()

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

	modelName := "gemini-2.5-flash"
	contents := []*genai.Content{
		{Parts: []*genai.Part{
			{Text: "What is shown in this image?"},
			{FileData: &genai.FileData{
				// Image source: https://storage.googleapis.com/cloud-samples-data/generative-ai/image/scones.jpg
				FileURI:  "gs://cloud-samples-data/generative-ai/image/scones.jpg",
				MIMEType: "image/jpeg",
			}},
		},
			Role: "user"},
	}

	resp, err := client.Models.GenerateContent(ctx, modelName, contents, nil)
	if err != nil {
		return fmt.Errorf("failed to generate content: %w", err)
	}

	respText := resp.Text()

	fmt.Fprintln(w, respText)

	// Example response:
	// The image shows an overhead shot of a rustic, artistic arrangement on a surface that ...

	return nil
}

Node.js

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

const GOOGLE_CLOUD_PROJECT = process.env.GOOGLE_CLOUD_PROJECT;
const GOOGLE_CLOUD_LOCATION = process.env.GOOGLE_CLOUD_LOCATION || 'global';

async function generateContent(
  projectId = GOOGLE_CLOUD_PROJECT,
  location = GOOGLE_CLOUD_LOCATION
) {
  const ai = new GoogleGenAI({
    vertexai: true,
    project: projectId,
    location: location,
  });

  const image = {
    fileData: {
      fileUri: 'gs://cloud-samples-data/generative-ai/image/scones.jpg',
      mimeType: 'image/jpeg',
    },
  };

  const response = await ai.models.generateContent({
    model: 'gemini-2.5-flash',
    contents: [image, 'What is shown in this image?'],
  });

  console.log(response.text);

  return response.text;
}

Java

import com.google.genai.Client;
import com.google.genai.types.Content;
import com.google.genai.types.GenerateContentResponse;
import com.google.genai.types.HttpOptions;
import com.google.genai.types.Part;

public class TextGenerationWithTextAndImage {

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

  // Generates text with text and image input
  public static String generateContent(String modelId) {
    // Initialize client that will be used to send requests. This client only needs to be created
    // once, and can be reused for multiple requests.
    try (Client client =
        Client.builder()
            .location("global")
            .vertexAI(true)
            .httpOptions(HttpOptions.builder().apiVersion("v1").build())
            .build()) {

      GenerateContentResponse response =
          client.models.generateContent(
              modelId,
              Content.fromParts(
                  Part.fromText("What is shown in this image?"),
                  Part.fromUri(
                      "gs://cloud-samples-data/generative-ai/image/scones.jpg", "image/jpeg")),
              null);

      System.out.print(response.text());
      // Example response:
      // The image shows a flat lay of blueberry scones arranged on parchment paper. There are ...
      return response.text();
    }
  }
}

Code execution

The Gemini API in Vertex AI code execution feature enables the model to generate and run Python code and learn iteratively from the results until it arrives at a final output. Vertex AI provides code execution as a tool, similar to function calling. You can use this code execution capability to build applications that benefit from code-based reasoning and that produce text output. For example:

Python

from google import genai
from google.genai.types import (
    HttpOptions,
    Tool,
    ToolCodeExecution,
    GenerateContentConfig,
)

client = genai.Client(http_options=HttpOptions(api_version="v1"))
model_id = "gemini-2.5-flash"

code_execution_tool = Tool(code_execution=ToolCodeExecution())
response = client.models.generate_content(
    model=model_id,
    contents="Calculate 20th fibonacci number. Then find the nearest palindrome to it.",
    config=GenerateContentConfig(
        tools=[code_execution_tool],
        temperature=0,
    ),
)
print("# Code:")
print(response.executable_code)
print("# Outcome:")
print(response.code_execution_result)

# Example response:
# # Code:
# def fibonacci(n):
#     if n <= 0:
#         return 0
#     elif n == 1:
#         return 1
#     else:
#         a, b = 0, 1
#         for _ in range(2, n + 1):
#             a, b = b, a + b
#         return b
#
# fib_20 = fibonacci(20)
# print(f'{fib_20=}')
#
# # Outcome:
# fib_20=6765

Go

import (
	"context"
	"fmt"
	"io"

	genai "google.golang.org/genai"
)

// generateWithCodeExec shows how to generate text using the code execution tool.
func generateWithCodeExec(w io.Writer) error {
	ctx := context.Background()

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

	prompt := "Calculate 20th fibonacci number. Then find the nearest palindrome to it."
	contents := []*genai.Content{
		{Parts: []*genai.Part{
			{Text: prompt},
		},
			Role: "user"},
	}
	config := &genai.GenerateContentConfig{
		Tools: []*genai.Tool{
			{CodeExecution: &genai.ToolCodeExecution{}},
		},
		Temperature: genai.Ptr(float32(0.0)),
	}
	modelName := "gemini-2.5-flash"

	resp, err := client.Models.GenerateContent(ctx, modelName, contents, config)
	if err != nil {
		return fmt.Errorf("failed to generate content: %w", err)
	}

	for _, p := range resp.Candidates[0].Content.Parts {
		if p.Text != "" {
			fmt.Fprintf(w, "Gemini: %s", p.Text)
		}
		if p.ExecutableCode != nil {
			fmt.Fprintf(w, "Language: %s\n%s\n", p.ExecutableCode.Language, p.ExecutableCode.Code)
		}
		if p.CodeExecutionResult != nil {
			fmt.Fprintf(w, "Outcome: %s\n%s\n", p.CodeExecutionResult.Outcome, p.CodeExecutionResult.Output)
		}
	}

	// Example response:
	// Gemini: Okay, I can do that. First, I'll calculate the 20th Fibonacci number. Then, I need ...
	//
	// Language: PYTHON
	//
	// def fibonacci(n):
	//    ...
	//
	// fib_20 = fibonacci(20)
	// print(f'{fib_20=}')
	//
	// Outcome: OUTCOME_OK
	// fib_20=6765
	//
	// Now that I have the 20th Fibonacci number (6765), I need to find the nearest palindrome. ...
	// ...

	return nil
}

Node.js

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

const GOOGLE_CLOUD_PROJECT = process.env.GOOGLE_CLOUD_PROJECT;
const GOOGLE_CLOUD_LOCATION = process.env.GOOGLE_CLOUD_LOCATION || 'global';

async function generateContent(
  projectId = GOOGLE_CLOUD_PROJECT,
  location = GOOGLE_CLOUD_LOCATION
) {
  const ai = new GoogleGenAI({
    vertexai: true,
    project: projectId,
    location: location,
  });

  const MODEL_NAME = 'gemini-2.5-flash';

  const response = await ai.models.generateContent({
    model: MODEL_NAME,
    contents:
      'What is the sum of the first 50 prime numbers? Generate and run code for the calculation, and make sure you get all 50.',
    config: {
      tools: [{codeExecution: {}}],
      temperature: 0,
    },
  });

  console.debug(response.executableCode);
  console.debug(response.codeExecutionResult);

  return response.codeExecutionResult;
}

For more examples of code execution, check out the code execution documentation.

What's next

Now that you made your first API request, you might want to explore the following guides that show how to set up more advanced Vertex AI features for production code:

• Google Gen AI libraries
• OpenAI compatibility