feat(js/plugins/anthropic): add anthropic plugin core implementation

js/plugins/anthropic/.gitignore

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+lib/
+node_modules/
+coverage/

js/plugins/anthropic/.npmignore

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+# typescript source files
+src/
+tests/
+tsconfig.json
+tsup.common.ts
+tsup.config.ts
+
+# GitHub files
+.github/
+.gitignore
+.npmignore
+CODE_OF_CONDUCT.md
+CONTRIBUTING.md
+
+# Developer related files
+.devcontainer/
+.vscode/

js/plugins/anthropic/NOTICE

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+This project includes code derived from the Firebase Genkit Anthropic community plugin
+(https://github.com/BloomLabsInc/genkit-plugins/tree/main/plugins/anthropic).
+
+Copyright 2024 Bloom Labs Inc.
+Copyright 2025 Google LLC.
+
+Licensed under the Apache License, Version 2.0.
+See the LICENSE file distributed with this project for the full license text.

js/plugins/anthropic/README.md

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+# Firebase Genkit + Anthropic AI
+
+<h1 align="center">Firebase Genkit <> Anthropic AI Plugin</h1>
+
+<h4 align="center">Anthropic AI plugin for Google Firebase Genkit</h4>
+
+`@genkit-ai/anthropic` is the official Anthropic plugin for [Firebase Genkit](https://github.com/firebase/genkit). It supersedes the earlier community package `genkitx-anthropic` and is now maintained by Google.
+
+## Supported models
+
+The plugin supports the most recent Anthropic models: **Claude Sonnet 4.5**, **Claude Opus 4.1**, **Claude Haiku 4.5**, **Claude Sonnet 4**, **Claude Opus 4**, **Claude 3.5 Haiku**, and **Claude 3 Haiku**.
+
+## Installation
+
+Install the plugin in your project with your favorite package manager:
+
+- `npm install @genkit-ai/anthropic`
+- `yarn add @genkit-ai/anthropic`
+- `pnpm add @genkit-ai/anthropic`
+
+## Usage
+
+### Initialize
+
+```typescript
+import { genkit } from 'genkit';
+import { anthropic } from '@genkit-ai/anthropic';
+
+const ai = genkit({
+  plugins: [anthropic({ apiKey: process.env.ANTHROPIC_API_KEY })],
+  // specify a default model for generate here if you wish:
+  model: anthropic.model('claude-sonnet-4-5'),
+});
+```
+
+### Basic examples
+
+The simplest way to generate text is by using the `generate` method:
+
+```typescript
+const response = await ai.generate({
+  model: anthropic.model('claude-3-haiku'),
+  prompt: 'Tell me a joke.',
+});
+
+console.log(response.text);
+```
+
+### Multi-modal prompt
+
+```typescript
+// ...initialize Genkit instance (as shown above)...
+
+const response = await ai.generate({
+  prompt: [
+    { text: 'What animal is in the photo?' },
+    { media: { url: imageUrl } },
+  ],
+  config: {
+    // control of the level of visual detail when processing image embeddings
+    // Low detail level also decreases the token usage
+    visualDetailLevel: 'low',
+  },
+});
+console.log(response.text);
+```
+
+### Extended thinking
+
+Claude 4 models can expose their internal reasoning. Enable it per-request with the Anthropic thinking config and read the reasoning from the response:
+
+```typescript
+const response = await ai.generate({
+  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 assistant answer
+console.log(response.reasoning);  // Summarized thinking steps
+```
+
+When thinking is enabled, request bodies sent through the plugin include the `thinking` payload (`{ type: 'enabled', budget_tokens: … }`) that Anthropic's API expects, and streamed responses deliver `reasoning` parts as they arrive so you can render the chain-of-thought incrementally.
+
+### Beta API Limitations
+
+The beta API surface provides access to experimental features, but some server-managed tool blocks are not yet supported by this plugin. The following beta API features will cause an error if encountered:
+
+- `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`
+
+Note that `server_tool_use` and `web_search_tool_result` ARE supported and work with both stable and beta APIs.
+
+### Within a flow
+
+```typescript
+import { z } from 'genkit';
+
+// ...initialize Genkit instance (as shown above)...
+
+export const jokeFlow = ai.defineFlow(
+  {
+    name: 'jokeFlow',
+    inputSchema: z.string(),
+    outputSchema: z.string(),
+  },
+  async (subject) => {
+    const llmResponse = await ai.generate({
+      prompt: `tell me a joke about ${subject}`,
+    });
+    return llmResponse.text;
+  }
+);
+```
+
+### Direct model usage (without Genkit instance)
+
+The plugin supports Genkit Plugin API v2, which allows you to use models directly without initializing the full Genkit framework:
+
+```typescript
+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);
+```
+
+You can also create model references using the plugin's `model()` method:
+
+```typescript
+import { anthropic } from '@genkit-ai/anthropic';
+
+// Create model references
+const claudeSonnet45 = anthropic.model('claude-sonnet-4-5');
+const claudeOpus41 = anthropic.model('claude-opus-4-1');
+const claude35Haiku = anthropic.model('claude-3-5-haiku');
+
+// Use the model reference directly
+const response = await claudeSonnet45({
+  messages: [
+    {
+      role: 'user',
+      content: [{ text: 'Hello!' }],
+    },
+  ],
+});
+```
+
+This approach is useful for:
+
+- Framework developers who need raw model access
+- Testing models in isolation
+- Using Genkit models in non-Genkit applications
+
+## Acknowledgements
+
+This plugin builds on the community work published as [`genkitx-anthropic`](https://github.com/BloomLabsInc/genkit-plugins/blob/main/plugins/anthropic/README.md) by Bloom Labs Inc. Their Apache 2.0–licensed implementation provided the foundation for this maintained package.
+
+## Contributing
+
+Want to contribute to the project? That's awesome! Head over to our [Contribution Guidelines](CONTRIBUTING.md).
+
+## Need support?
+
+> [!NOTE]
+> This repository depends on Google's Firebase Genkit. For issues and questions related to Genkit, please refer to instructions available in [Genkit's repository](https://github.com/firebase/genkit).
+
+
+## Credits
+
+This plugin is maintained by Google with acknowledgement to the community contributions from [Bloom Labs Inc](https://github.com/BloomLabsInc).
+
+## License
+
+This project is licensed under the [Apache 2.0 License](https://github.com/BloomLabsInc/genkit-plugins/blob/main/LICENSE).

js/plugins/anthropic/package.json

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+{
+  "name": "@genkit-ai/anthropic",
+  "description": "Genkit AI framework plugin for Anthropic APIs.",
+  "keywords": [
+    "genkit",
+    "genkit-plugin",
+    "genkit-model",
+    "anthropic",
+    "anthropic-ai",
+    "claude-4",
+    "haiku-4",
+    "opus",
+    "haiku",
+    "sonnet",
+    "ai",
+    "genai",
+    "generative-ai"
+  ],
+  "version": "1.21.0",
+  "type": "commonjs",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/firebase/genkit.git",
+    "directory": "js/plugins/anthropic"
+  },
+  "author": "genkit",
+  "license": "Apache-2.0",
+  "peerDependencies": {
+    "genkit": "workspace:^"
+  },
+  "dependencies": {
+    "@anthropic-ai/sdk": "^0.68.0"
+  },
+  "devDependencies": {
+    "@types/node": "^20.11.16",
+    "check-node-version": "^4.2.1",
+    "genkit": "workspace:*",
+    "npm-run-all": "^4.1.5",
+    "rimraf": "^6.0.1",
+    "tsup": "^8.3.5",
+    "tsx": "^4.19.2",
+    "typescript": "^4.9.0"
+  },
+  "types": "./lib/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./lib/index.d.ts",
+      "require": "./lib/index.js",
+      "import": "./lib/index.mjs",
+      "default": "./lib/index.js"
+    }
+  },
+  "files": [
+    "lib"
+  ],
+  "publishConfig": {
+    "provenance": true,
+    "access": "public"
+  },
+  "scripts": {
+    "check": "tsc",
+    "compile": "tsup-node",
+    "build:clean": "rimraf ./lib",
+    "build": "npm-run-all build:clean check compile",
+    "build:watch": "tsup-node --watch",
+    "test": "tsx --test tests/*_test.ts",
+    "test:file": "tsx --test",
+    "test:coverage": "check-node-version --node '>=22' && tsx --test --experimental-test-coverage --test-coverage-include='src/**/*.ts' ./tests/**/*_test.ts"
+  }
+}