SDKs · Updated 2026-07-21

Anthropic SDK

Integrate Anthropic Messages through the Varsten beta wrapper with direct-to-provider fallback before output starts.

Status

The Anthropic wrapper is version 0.1.0 beta and intended for founder-supervised pilots. It supports streaming and non-streaming Messages. Test tools, beta headers, and workload-specific options before production rollout.

Install

bash

npm install @varsten/anthropic @anthropic-ai/sdk

Node.js 18 or newer and ESM are required.

Create the client

import { VarstenAnthropic } from "@varsten/anthropic";

const client = new VarstenAnthropic({
  varstenApiKey: process.env.VARSTEN_API_KEY,
  anthropicApiKey: process.env.ANTHROPIC_API_KEY,
  onFallback: (event) => console.warn("varsten fallback", event.reasonCode),
});

const response = await client.messages.create({
  model: "claude-haiku-4-5-20251001",
  max_tokens: 256,
  messages: [{ role: "user", content: "Hello" }],
});

The Varsten key is sent only to Varsten. The Anthropic key stays in your application and is used by the direct fallback path.

Fallback boundary

The wrapper falls back for positively identified Varsten or transport failures before output starts. Relayed provider errors, deliberate budget caps, and mid-stream failures are surfaced instead of retried.