Use a context cache

You can use REST APIs or the Python SDK to reference content stored in a context cache in a generative AI application. Before it can be used, you must first create the context cache.

The context cache object you use in your code includes the following properties:

  • name - The context cache resource name. Its format is projects/PROJECT_NUMBER/locations/LOCATION/cachedContents/CACHE_ID. When you create a context cache, you can find its resource name is in the response. The project number is a unique identifier for your project. The cache ID is an ID for your cache. When you specify a context cache in your code, you must use the full context cache resource name. The following is an example that shows how you specify a cached content resource name in a request body:

    "cached_content": "projects/123456789012/locations/us-central1/123456789012345678"

  • model - The resource name for the model used to create the cache. Its format is projects/PROJECT_NUMBER/locations/LOCATION/publishers/PUBLISHER_NAME/models/MODEL_ID.

  • createTime - A Timestamp that specifies the create time of the context cache.

  • updateTime - A Timestamp that specifies the most recent update time of a context cache. After a context cache is created, and before it's updated, its createTime and updateTime are the same.

  • expireTime - A Timestamp that specifies when a context cache expires. The default expireTime is 60 minutes after the createTime. You can update the cache with a new expiration time. For more information, see Update the context cache. After a cache expires, it's marked for deletion and you shouldn't assume that it can be used or updated. If you need to use a context cache that expired, you need to recreate it with an appropriate expiration time.

Context cache use restrictions

The following features can be specified when you create a context cache. You shouldn't specify them again in your request:

  • The GenerativeModel.system_instructions property. This property is used to specify instructions to the model before the model receives instructions from a user. For more information, see System instructions.

  • The GenerativeModel.tool_config property. The tool_config property is used to specify tools used by the Gemini model, such as a tool used by the function calling feature.

  • The GenerativeModel.tools property. The GenerativeModel.tools property is used to specify functions to create a function calling application. For more information, see Function calling.

Use a context cache sample

The following shows how to use a context cache. When you use a context cache, you can't specify the following properties:

  • GenerativeModel.system_instructions
  • GenerativeModel.tool_config
  • GenerativeModel.tools

Gen AI SDK for Python

Install

pip install --upgrade google-genai
 To learn more, see the SDK reference documentation.

Set environment variables to use the Gen AI SDK with Vertex AI: 

# 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=us-central1
export GOOGLE_GENAI_USE_VERTEXAI=True
 

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

client = genai.Client(http_options=HttpOptions(api_version="v1beta1"))

# Use content cache to generate text response
# E.g cache_name = 'projects/111111111111/locations/us-central1/cachedContents/1111111111111111111'
response = client.models.generate_content(
    model="gemini-1.5-pro-002",
    contents="Summarize the pdfs",
    config=GenerateContentConfig(
        cached_content=cache_name,
    ),
)
print(response.text)
# Example response
#   The Gemini family of multimodal models from Google DeepMind demonstrates remarkable capabilities across various
#   modalities, including image, audio, video, and text....

Vertex AI SDK for Python

To learn how to install or update the Vertex AI SDK for Python, see Install the Vertex AI SDK for Python. For more information, see the Vertex AI SDK for Python API reference documentation. 

import vertexai

from vertexai.preview.generative_models import GenerativeModel
from vertexai.preview import caching

# TODO(developer): Update and un-comment below lines
# PROJECT_ID = "your-project-id"
# cache_id = "your-cache-id"

vertexai.init(project=PROJECT_ID, location="us-central1")

cached_content = caching.CachedContent(cached_content_name=cache_id)

model = GenerativeModel.from_cached_content(cached_content=cached_content)

response = model.generate_content("What are the papers about?")

print(response.text)
# Example response:
# The provided text is about a new family of multimodal models called Gemini, developed by Google.
# ...

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"
	"errors"
	"fmt"
	"io"

	"cloud.google.com/go/vertexai/genai"
)

// useContextCache shows how to use an existing cached content, when prompting the model
// contentName is the ID of the cached content
func useContextCache(w io.Writer, contentName string, projectID, location, modelName string) error {
	// location := "us-central1"
	// modelName := "gemini-1.5-pro-001"
	ctx := context.Background()

	client, err := genai.NewClient(ctx, projectID, location)
	if err != nil {
		return fmt.Errorf("unable to create client: %w", err)
	}
	defer client.Close()

	model := client.GenerativeModel(modelName)
	model.CachedContentName = contentName
	prompt := genai.Text("What are the papers about?")

	res, err := model.GenerateContent(ctx, prompt)
	if err != nil {
		return fmt.Errorf("error generating content: %w", err)
	}

	if len(res.Candidates) == 0 ||
		len(res.Candidates[0].Content.Parts) == 0 {
		return errors.New("empty response from model")
	}

	fmt.Fprintf(w, "generated response: %s\n", res.Candidates[0].Content.Parts[0])
	return nil
}

C#

Before trying this sample, follow the C# setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI C# 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. 


using Google.Cloud.AIPlatform.V1Beta1;
using System;
using System.Threading.Tasks;

public class UseContextCache
{
    public async Task<string> Use(string projectId, CachedContentName name)
    {
        var predictionServiceClient = new PredictionServiceClientBuilder
        {
            Endpoint = $"us-central1-aiplatform.googleapis.com"
        }.Build();

        var generateContentRequest = new GenerateContentRequest
        {
            CachedContentAsCachedContentName = name,
            Model = $"projects/{projectId}/locations/us-central1/publishers/google/models/gemini-1.5-pro-001",
            Contents =
            {
                new Content
                {
                    Role = "USER",
                    Parts =
                    {
                        new Part { Text = "What are the papers about?" },
                    }
                }
            }
        };

        GenerateContentResponse response = await predictionServiceClient.GenerateContentAsync(generateContentRequest);

        string responseText = response.Candidates[0].Content.Parts[0].Text;
        Console.WriteLine($"Response: {responseText}");

        return responseText;
    }
}

REST

You can use REST to use a context cache with a prompt by using the Vertex AI API to send a POST request to the publisher model endpoint.

Before using any of the request data, make the following replacements:

HTTP method and URL: 

POST https://LOCATION-aiplatform.googleapis.com/v1/projects/PROJECT_ID/locations/LOCATION/publishers/google/models/gemini-1.5-pro-002:generateContent

Request JSON body: 

{
  "cachedContent": "projects/PROJECT_NUMBER/locations/LOCATION/cachedContents/CACHE_ID",
  "contents": [
      {"role":"user","parts":[{"text":"PROMPT_TEXT"}]}
  ],
  "generationConfig": {
      "maxOutputTokens": 8192,
      "temperature": 1,
      "topP": 0.95,
  },
  "safetySettings": [
      {
          "category": "HARM_CATEGORY_HATE_SPEECH",
          "threshold": "BLOCK_MEDIUM_AND_ABOVE"
      },
      {
          "category": "HARM_CATEGORY_DANGEROUS_CONTENT",
          "threshold": "BLOCK_MEDIUM_AND_ABOVE"
      },
      {
          "category": "HARM_CATEGORY_SEXUALLY_EXPLICIT",
          "threshold": "BLOCK_MEDIUM_AND_ABOVE"
      },
      {
          "category": "HARM_CATEGORY_HARASSMENT",
          "threshold": "BLOCK_MEDIUM_AND_ABOVE"
      }
  ],
}

To send your request, choose one of these options:

curl

Save the request body in a file named request.json, and execute the following command: 

curl -X POST \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json; charset=utf-8" \
     -d @request.json \
     "https://LOCATION-aiplatform.googleapis.com/v1/projects/PROJECT_ID/locations/LOCATION/publishers/google/models/gemini-1.5-pro-002:generateContent"

PowerShell

Save the request body in a file named request.json, and execute the following command: 

$cred = gcloud auth print-access-token
$headers = @{ "Authorization" = "Bearer $cred" }

Invoke-WebRequest `
    -Method POST `
    -Headers $headers `
    -ContentType: "application/json; charset=utf-8" `
    -InFile request.json `
    -Uri "https://LOCATION-aiplatform.googleapis.com/v1/projects/PROJECT_ID/locations/LOCATION/publishers/google/models/gemini-1.5-pro-002:generateContent" | Select-Object -Expand Content

You should receive a JSON response similar to the following.

Example curl command

LOCATION="us-central1"
MODEL_ID="gemini-1.5-pro-002"
PROJECT_ID="test-project"

curl -X POST \
-H "Authorization: Bearer $(gcloud auth print-access-token)" \
-H "Content-Type: application/json" \
"https://${LOCATION}-aiplatform.googleapis.com/v1/projects/${PROJECT_ID}/locations/${LOCATION}/publishers/google/models/${MODEL_ID}:generateContent" -d \
'{
  "cachedContent": "projects/${PROJECT_NUMBER}/locations/${LOCATION}/cachedContents/${CACHE_ID}",
  "contents": [
      {"role":"user","parts":[{"text":"What are the benefits of exercise?"}]}
  ],
  "generationConfig": {
      "maxOutputTokens": 8192,
      "temperature": 1,
      "topP": 0.95,
  },
  "safetySettings": [
    {
      "category": "HARM_CATEGORY_HATE_SPEECH",
      "threshold": "BLOCK_MEDIUM_AND_ABOVE"
    },
    {
      "category": "HARM_CATEGORY_DANGEROUS_CONTENT",
      "threshold": "BLOCK_MEDIUM_AND_ABOVE"
    },
    {
      "category": "HARM_CATEGORY_SEXUALLY_EXPLICIT",
      "threshold": "BLOCK_MEDIUM_AND_ABOVE"
    },
    {
      "category": "HARM_CATEGORY_HARASSMENT",
      "threshold": "BLOCK_MEDIUM_AND_ABOVE"
    }
  ],
}'