Create a chat session with a Generative Model

This sample demonstrates how to use Generative Models to create a chat session.

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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"
)

// generateChatWithText shows how to generate chat using a text prompt.
func generateChatWithText(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"
	history := []*genai.Content{
		{
			Role: "user",
			Parts: []*genai.Part{
				{Text: "Hello there"},
			},
		},
		{
			Role: "model",
			Parts: []*genai.Part{
				{Text: "Great to meet you. What would you like to know?"},
			},
		},
	}
	chatSession, err := client.Chats.Create(ctx, modelName, nil, history)
	if err != nil {
		return fmt.Errorf("failed to create genai chat session: %w", err)
	}
	contents := genai.Part{Text: "Tell me a story."}
	resp, err := chatSession.SendMessage(ctx, contents)
	if err != nil {
		return fmt.Errorf("failed to send message: %w", err)
	}

	respText := resp.Text()

	fmt.Fprintln(w, respText)
	// Example response:
	// Okay, settle in. Let me tell you a story about a quiet cartographer, but not of lands and seas.
	// ...
	// In the sleepy town of Oakhaven, nestled between the Whispering Hills and the Murmuring River, lived a woman named Elara.
	// ...

	return nil
}

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

client = genai.Client(http_options=HttpOptions(api_version="v1"))
chat_session = client.chats.create(
    model="gemini-2.5-flash",
    history=[
        UserContent(parts=[Part(text="Hello")]),
        ModelContent(
            parts=[Part(text="Great to meet you. What would you like to know?")],
        ),
    ],
)
response = chat_session.send_message("Tell me a story.")
print(response.text)
# Example response:
# Okay, here's a story for you:
# ...

What's next

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