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Anthropic Plugin

The @genkit-ai/anthropic plugin provides access to Anthropic’s Claude models, including the latest Claude 4.5 series (Haiku, Sonnet, Opus). This plugin is now officially maintained by Google and supersedes the earlier community package genkitx-anthropic.

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Installation

npm install @genkit-ai/anthropic
Or with other package managers: 
yarn add @genkit-ai/anthropic
pnpm add @genkit-ai/anthropic

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Supported Models

The plugin supports the most recent Anthropic models:
  • Claude Haiku 4.5 (claude-haiku-4-5) - Fast, cost-effective
  • Claude Sonnet 4.5 (claude-sonnet-4-5) - Balanced performance
  • Claude Opus 4.5 (claude-opus-4-5) - Most capable
Plus all non-retired older models including Claude 3.5 and 3.0 series.

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Basic Setup

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Initialize the Plugin

import { genkit } from 'genkit';
import { anthropic } from '@genkit-ai/anthropic';

const ai = genkit({
  plugins: [anthropic({ apiKey: process.env.ANTHROPIC_API_KEY })],
  model: anthropic.model('claude-sonnet-4-5'), // Optional default
});

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Simple Text Generation

const response = await ai.generate({
  model: anthropic.model('claude-haiku-4-5'),
  prompt: 'Tell me a joke.',
});

console.log(response.text);

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Features

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Multi-modal Prompts

Claude supports text and image inputs: 
const response = await ai.generate({
  model: anthropic.model('claude-sonnet-4-5'),
  prompt: [
    { text: 'What animal is in the photo?' },
    { media: { url: imageUrl } },
  ],
});

console.log(response.text);

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Extended Thinking

Claude 4.5 models can expose their internal reasoning process: 
const response = await ai.generate({
  model: anthropic.model('claude-sonnet-4-5'),
  prompt: 'Walk me through your reasoning for Fermat\'s little theorem.',
  config: {
    thinking: {
      enabled: true,
      budgetTokens: 4096, // Must be >= 1024 and less than max_tokens
    },
  },
});

console.log(response.text);      // Final answer
console.log(response.reasoning); // Thinking steps
When thinking is enabled:
  • Request bodies include the thinking payload
  • Streamed responses deliver reasoning parts incrementally
  • You can render the chain-of-thought as it arrives

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Document Citations

Claude can cite specific parts of documents, making it easy to trace information sources. Use the anthropicDocument() helper: 
import { anthropic, anthropicDocument } from '@genkit-ai/anthropic';

const response = await ai.generate({
  model: anthropic.model('claude-sonnet-4-5'),
  messages: [
    {
      role: 'user',
      content: [
        anthropicDocument({
          source: {
            type: 'text',
            data: 'The grass is green. The sky is blue. Water is wet.',
          },
          title: 'Basic Facts',
          citations: { enabled: true },
        }),
        { text: 'What color is the grass? Cite your source.' },
      ],
    },
  ],
});

// Access citations from response parts
const citations = response.message?.content?.flatMap(
  (part) => part.metadata?.citations || [],
) ?? [];

console.log('Citations:', citations);
Important: Citations must be enabled on all documents in a request, or on none. You cannot mix cited and non-cited documents. Supported document source types:
  • text - Plain text (returns char_location citations)
  • base64 - Base64-encoded PDFs (returns page_location citations)
  • url - PDFs via URL (returns page_location citations)
  • content - Custom content blocks (returns content_block_location citations)
  • file - Anthropic Files API references, beta only (returns page_location citations)

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Prompt Caching

Cache prompts to reduce costs and latency for repeated requests: 
import { anthropic, cacheControl } from '@genkit-ai/anthropic';

const response = await ai.generate({
  model: anthropic.model('claude-sonnet-4-5'),
  system: {
    text: longSystemPrompt,
    metadata: { ...cacheControl() }, // Default: ephemeral
  },
  messages: [
    {
      role: 'user',
      content: [{ text: 'What is the main idea of the text?' }],
    },
  ],
});
Cache control options: 
// Default ephemeral cache
metadata: { ...cacheControl() }

// Explicit TTL
metadata: { ...cacheControl({ ttl: '1h' }) }

// Using the type directly
import { type AnthropicCacheControl } from '@genkit-ai/anthropic';
metadata: { 
  cache_control: { 
    type: 'ephemeral', 
    ttl: '5m' 
  } as AnthropicCacheControl 
}
Note: Caching only activates when prompts exceed a minimum token length. See Anthropic API documentation for details.

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Using in Flows

import { z } from 'genkit';

const jokeFlow = ai.defineFlow(
  {
    name: 'jokeFlow',
    inputSchema: z.string(),
    outputSchema: z.string(),
  },
  async (subject) => {
    const llmResponse = await ai.generate({
      model: anthropic.model('claude-haiku-4-5'),
      prompt: `Tell me a joke about ${subject}`,
    });
    return llmResponse.text;
  }
);

// Use the flow
const joke = await jokeFlow('programming');
console.log(joke);

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Direct Model Usage (Plugin API v2)

The plugin supports using models directly without initializing the full Genkit framework: 
import { anthropic } from '@genkit-ai/anthropic';

// Create a model reference directly
const claude = anthropic.model('claude-sonnet-4-5');

// Use the model directly
const response = await claude({
  messages: [
    {
      role: 'user',
      content: [{ text: 'Tell me a joke.' }],
    },
  ],
});

console.log(response);
Multiple model references: 
import { anthropic } from '@genkit-ai/anthropic';

const claudeHaiku45 = anthropic.model('claude-haiku-4-5');
const claudeSonnet45 = anthropic.model('claude-sonnet-4-5');
const claudeOpus45 = anthropic.model('claude-opus-4-5');

const response = await claudeSonnet45({
  messages: [
    {
      role: 'user',
      content: [{ text: 'Hello!' }],
    },
  ],
});
This approach is useful for:
  • Framework developers needing raw model access
  • Testing models in isolation
  • Using Genkit models in non-Genkit applications

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Beta API Limitations

The beta API provides access to experimental features, but some server-managed tool blocks are not yet supported: Not supported:
  • web_fetch_tool_result
  • code_execution_tool_result
  • bash_code_execution_tool_result
  • text_editor_code_execution_tool_result
  • mcp_tool_result
  • mcp_tool_use
  • container_upload
Supported:
  • server_tool_use ✅
  • web_search_tool_result ✅
These work with both stable and beta APIs.

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Configuration Options

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Plugin Options

anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY,  // Required
  apiVersion: '2023-06-01',               // Optional, API version
})

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Model Config

const response = await ai.generate({
  model: anthropic.model('claude-sonnet-4-5'),
  prompt: 'Your prompt',
  config: {
    temperature: 0.7,              // Randomness (0.0-1.0)
    maxOutputTokens: 2048,         // Max response length
    topP: 0.9,                     // Nucleus sampling
    topK: 40,                      // Top-K sampling
    stopSequences: ['END'],        // Stop sequences
    thinking: {                    // Extended thinking
      enabled: true,
      budgetTokens: 4096,
    },
  },
});

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Best Practices

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Model Selection

  • Claude Haiku 4.5 - Use for fast, cost-effective tasks
  • Claude Sonnet 4.5 - Best for most production use cases
  • Claude Opus 4.5 - Use for complex reasoning and research

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Error Handling

try {
  const response = await ai.generate({
    model: anthropic.model('claude-sonnet-4-5'),
    prompt: 'Your prompt',
  });
  console.log(response.text);
} catch (error) {
  console.error('Anthropic API error:', error);
  // Handle rate limits, invalid requests, etc.
}

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Streaming Responses

const response = await ai.generate({
  model: anthropic.model('claude-sonnet-4-5'),
  prompt: 'Write a long story',
  stream: true,
  onChunk: (chunk) => {
    console.log('Chunk:', chunk.text);
  },
});

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Acknowledgements

This plugin builds on community work published as genkitx-anthropic by Bloom Labs Inc. Their Apache 2.0-licensed implementation provided the foundation for this maintained package.

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