x402-anthropic-typescript

x402 payment transport for the Anthropic TypeScript SDK.

Wrap the standard Anthropic client with a crypto wallet. When the server responds with HTTP 402, the library automatically signs a USDC payment and retries — zero code changes needed. Follows the pattern introduced by qntx/x402-openai-typescript.

Install

npm install x402-anthropic @x402/evm viem        # EVM (Base, Ethereum)
npm install x402-anthropic @x402/svm @solana/kit  # SVM (Solana)
npm install x402-anthropic @x402/evm @x402/svm viem @solana/kit  # all chains

Quick start

import { X402Anthropic, EVMWallet } from "x402-anthropic";

const client = new X402Anthropic({
  wallet: new EVMWallet("0x..."),
  baseURL: "https://your-x402-gateway.example.com",
});

const message = await client.messages.create({
  model: "claude-opus-4-5",
  max_tokens: 1024,
  messages: [{ role: "user", content: "Hello!" }],
});
console.log(message.content[0]);

Swap EVMWallet for SVMWallet to pay on Solana — the API is identical.

Usage

Streaming

const stream = await client.messages.stream({
  model: "claude-opus-4-5",
  max_tokens: 1024,
  messages: [{ role: "user", content: "Tell me a story." }],
});
for await (const text of stream.textStream) {
  process.stdout.write(text);
}

Payment policies

import { X402Anthropic, EVMWallet, preferNetwork, maxAmount } from "x402-anthropic";

const client = new X402Anthropic({
  wallet: new EVMWallet("0x..."),
  policies: [preferNetwork("eip155:8453"), maxAmount(1_000_000n)],  // Base, max $1 USDC
  baseURL: "...",
});

Safety: use a dedicated wallet with limited funds and always set a maxAmount policy before pointing this at an untrusted gateway.

API reference

X402Anthropic

Drop-in replacement for Anthropic from @anthropic-ai/sdk.

| Parameter | Type | Description | | :-- | :-- | :-- | | wallet | Wallet | Wallet adapter for signing payments | | policies | Policy[] | Payment policies (chain preference, amount cap) | | baseURL | string | Gateway URL (required — points at your x402 server) |

All standard Anthropic options (timeout, maxRetries, apiKey, …) are forwarded.

Wallet adapters

| Class | Chain | Peer deps | | :-- | :-- | :-- | | EVMWallet(privateKey) | Base, Ethereum, any EVM | @x402/evm viem | | SVMWallet(privateKey) | Solana | @x402/svm @solana/kit |

Implement the Wallet interface to add a new chain.

Policy helpers

| Function | Effect | | :-- | :-- | | preferNetwork(caip2) | Prefer a specific chain (falls back to any if unavailable) | | preferScheme(scheme) | Prefer a payment scheme (e.g. "exact") | | maxAmount(units) | Skip payment requirements above this USDC unit amount |

Examples

EVM_PRIVATE_KEY="0x..."        npx tsx examples/basic.ts
EVM_PRIVATE_KEY="0x..."        npx tsx examples/streaming.ts

Related

• x402-anthropic-python — Python version of this library
• qntx/x402-openai-typescript — OpenAI SDK equivalent
• coinbase/x402 — x402 protocol spec and reference implementation

License

MIT