Anthropic

The Anthropic adapter calls Claude for chat. It supports thinking, automatic prompt caching, and tools that Anthropic runs.

1. Install#

npm i @tanstack/ai-anthropic

pnpm add @tanstack/ai-anthropic

yarn add @tanstack/ai-anthropic

bun add @tanstack/ai-anthropic

2. Set the API key#

Put the key in the environment of your server:

ANTHROPIC_API_KEY=sk-ant-...

anthropicText, anthropicSummarize, and anthropicFiles use the first of these variables that is set:

1. ANTHROPIC_AUTH_TOKEN: sent as a Bearer token. An sk-ant-oat token here turns on OAuth mode.
2. ANTHROPIC_OAUTH_TOKEN: sent as a Bearer token, in OAuth mode.
3. ANTHROPIC_API_KEY: sent as x-api-key.

If none of them is set, these factories throw. To pass the credential in code, use createAnthropicChat. The create* factories never read a credential from the environment:

import { createAnthropicChat } from "@tanstack/ai-anthropic";

const adapter = createAnthropicChat("claude-sonnet-5-5", process.env.ANTHROPIC_API_KEY!);

Got a Bearer or OAuth token? See Bearer and OAuth tokens.

3. Stream a chat from the server#

import {
  chat,
  chatParamsFromRequest,
  toServerSentEventsResponse,
} from "@tanstack/ai";
import { anthropicText } from "@tanstack/ai-anthropic";

export async function POST(request: Request) {
  const { messages, threadId, runId } = await chatParamsFromRequest(request);

  const stream = chat({
    adapter: anthropicText("claude-sonnet-5-5"),
    messages,
    threadId,
    runId,
  });

  return toServerSentEventsResponse(stream);
}

4. Render the chat#

The client is the same for every provider. Point useChat at your route:

import { useState } from "react";
import { useChat, fetchServerSentEvents } from "@tanstack/ai-react";

export function Chat() {
  const [input, setInput] = useState("");
  const { messages, sendMessage } = useChat({
    connection: fetchServerSentEvents("/api/chat"),
    threadId: "support-chat",
  });

  return (
    <form
      onSubmit={(event) => {
        event.preventDefault();
        sendMessage(input);
        setInput("");
      }}
    >
      {messages.map((message) => (
        <p key={message.id}>
          {message.parts
            .map((part) => (part.type === "text" ? part.content : ""))
            .join("")}
        </p>
      ))}
      <input value={input} onChange={(event) => setInput(event.target.value)} />
    </form>
  );
}

For Vue, Solid, Svelte, Angular, and the other frameworks, see Quick Start.

You now have a streaming Claude chat. Tools and Structured Outputs work the same as with every adapter.

Summarization#

import { summarize } from "@tanstack/ai";
import { anthropicSummarize } from "@tanstack/ai-anthropic";

const result = await summarize({
  adapter: anthropicSummarize("claude-sonnet-4-6"),
  text: "Your long text to summarize...",
  threadId: "thread-1",
  maxLength: 100,
  style: "concise", // "concise" | "bullet-points" | "paragraph"
});

console.log(result.summary);

Files#

anthropicFiles uploads media to the Anthropic Files API, so a message can point to the file. See Files API.

No image generation#

Anthropic does not make images. For images, use OpenAI or Gemini.

Provider tools#

Anthropic runs some tools itself, such as web search and a code sandbox. Import them from @tanstack/ai-anthropic/tools and add them to tools:

import { chat } from "@tanstack/ai";
import { anthropicText } from "@tanstack/ai-anthropic";
import { webSearchTool } from "@tanstack/ai-anthropic/tools";

const stream = chat({
  adapter: anthropicText("claude-sonnet-5-5"),
  messages: [{ role: "user", content: "What's new in AI this week?" }],
  threadId: "thread-1",
  tools: [
    webSearchTool({
      name: "web_search",
      type: "web_search_20250305",
      max_uses: 2,
    }),
  ],
});

Tools that Anthropic runs:

• webSearchTool: search the web, with citations.
• webFetchTool: read one URL.
• codeExecutionTool: run code in a sandbox, also with hosted skills.
• memoryTool: keep facts across turns.

Tools that your app runs when Claude asks:

• bashTool: run shell commands.
• textEditorTool: view and change files.
• computerUseTool: control a virtual desktop.
• customTool: a tool with an inline schema.

Each tool, with a full sample, is on Anthropic: Advanced. For which models take which tool, see Provider Tools.

Models and options#

Model options#

Provider options go in modelOptions, with the Anthropic names:

import { chat } from "@tanstack/ai";
import { anthropicText } from "@tanstack/ai-anthropic";

const stream = chat({
  adapter: anthropicText("claude-sonnet-5-5"),
  messages: [{ role: "user", content: "Hello!" }],
  threadId: "thread-1",
  modelOptions: {
    max_tokens: 4096,
    stop_sequences: ["END"],
  },
});

• The sampling options temperature, top_p, and top_k also go in modelOptions. Claude Sonnet 5, Claude Opus 4.7 and later, and the 5-generation models reject them. The types take them only on the models that accept them, for example claude-sonnet-4-6.
• When you do not set max_tokens, the adapter sends the full output limit of the model. See The max_tokens default.
• Sampling options do not go at the root of chat(). See Moving Sampling Options into modelOptions.

Reasoning#

Want Claude to think harder, or not at all? Set reasoning on chat(). The adapter turns the level into the right thinking fields for the model.

import { chat } from "@tanstack/ai";
import { anthropicText } from "@tanstack/ai-anthropic";

const stream = chat({
  adapter: anthropicText("claude-opus-5-5"),
  messages: [{ role: "user", content: "Plan a database migration." }],
  threadId: "thread-1",
  reasoning: "xhigh",
});

What goes to Anthropic:

• off sends thinking: { type: "disabled" } on the models with off in the table below. On a model without off, such as claude-fable-5, the types reject it. At run time, it moves to the lowest level that the model has.
• Claude 4.6 and later get adaptive thinking and output_config.effort. With an outputSchema, the adapter adds output_config.format next to the effort.
• Budget models get thinking: { type: "enabled", budget_tokens }. The level picks the budget, or you set it with budgetTokens. If max_tokens is below the budget, the adapter raises it.
• summary: false sends display: "omitted", so the thinking text does not stream.

The levels of each model:

A budget model with budgetTokens:

import { chat } from "@tanstack/ai";
import { anthropicText } from "@tanstack/ai-anthropic";

const stream = chat({
  adapter: anthropicText("claude-haiku-4-5"),
  messages: [{ role: "user", content: "Check this proof." }],
  threadId: "thread-1",
  reasoning: { level: "high", budgetTokens: 8000 },
});

Structured output forces a tool, and Claude cannot think while a tool is forced. So the structured output call sends no thinking. See Reasoning for the levels and the nearest-level rule.

Models#

Newest first. The package exports the full list as ANTHROPIC_MODELS.

adapter.inputModalities lists the input kinds of the selected model. See Check what a model accepts.

Refusal fallback#

Did Claude return an empty answer to a life-science or security question? A safety classifier on the newer models can decline a request. Set fallbacks, and the Claude API sends a declined request to another Claude model in the same call:

import { chat, toServerSentEventsResponse } from "@tanstack/ai";
import { anthropicText } from "@tanstack/ai-anthropic";

export async function POST(request: Request) {
  const { messages } = await request.json();

  const stream = chat({
    adapter: anthropicText("claude-opus-5-5"),
    messages,
    threadId: "thread-1",
    modelOptions: { fallbacks: "default" },
  });

  return toServerSentEventsResponse(stream);
}

What this does:

• "default" uses the model that Anthropic recommends for the refusal category. A list, such as [{ model: "claude-opus-4-8" }], names up to three models to try in order.
• The adapter adds the server-side-fallback-2026-07-01 beta header for you.
• The fallback answer streams like any other answer. When text has already started, events before the fallback block name the model that declined. That includes RUN_STARTED and that first text segment. Events after the block name to.model.
• When the classifier declines before any output, message_start already names the fallback model. RUN_STARTED uses that name too.
• The types accept fallbacks on claude-fable-5, claude-fable-5-1, claude-opus-5, claude-opus-5-5, and claude-sonnet-5-5.

Some refusals still stand. For example, a category can have no recommended model, or the fallback model can be busy. Then the run ends with finishReason: "content_filter", not with an error. The rawEvent of that RUN_FINISHED holds the Anthropic stop_details, with category and explanation.

Show the reason in the UI with onChunk:

import { useState } from "react";
import { fetchServerSentEvents, useChat } from "@tanstack/ai-react";

export function Chat() {
  const [refusal, setRefusal] = useState<string | null>(null);

  const { messages, sendMessage } = useChat({
    connection: fetchServerSentEvents("/api/chat"),
    threadId: "support-chat",
    onChunk: (chunk) => {
      if (chunk.type === "RUN_FINISHED" && chunk.finishReason === "content_filter") {
        const details = chunk.rawEvent;
        const category =
          details &&
          typeof details === "object" &&
          "category" in details &&
          typeof details.category === "string"
            ? details.category
            : "unknown";
        setRefusal(`Claude declined this request (category: ${category}).`);
      }
    },
  });

  return (
    <div>
      {messages.map((message) => (
        <p key={message.id}>
          {message.parts.map((part) => (part.type === "text" ? part.content : null))}
        </p>
      ))}
      {refusal && <p role="alert">{refusal}</p>}
      <button onClick={() => sendMessage("Describe how CRISPR edits a gene.")}>Send</button>
    </div>
  );
}

Limits:

• Fallback works only on the Claude API. Claude on Vertex does not have it.
• claude-haiku-5-5 has no fallback model, so its refusals always stand.
• The adapter does not send the fallback content block back on the next turn. A refusal before any output is not affected.

Now a declined request gets an answer from a fallback model. When no model can answer, your UI tells the user why.

Advanced#

These topics are on Anthropic: Advanced:

• Bearer and OAuth tokens, gateways, and your own Anthropic client.
• Claude on Vertex AI.
• The max_tokens default and prompt caching.
• Every provider tool, with a full sample.
• The API reference.

To call Claude through a GitHub Copilot plan, see GitHub Copilot.