x402

x402 is an open HTTP standard that revives the long-dormant 402 Payment Required status code so that any HTTP endpoint can charge for individual requests. When a client (typically an AI agent) hits a paid endpoint, the server replies with a 402 response containing a machine-readable payment instruction — currency, amount, recipient, accepted chains, payment reference. The client pays, retries the request with proof of payment, and gets the response.

Why it matters for AI agents

Traditional API monetization assumes a human creates an account, gets an API key, and pays monthly. AI agents don’t fit that model — they discover endpoints at runtime, transact in micro-amounts, and shouldn’t share a single API key across an entire fleet of agents. x402 collapses signup, billing, and authentication into one round-trip per call.

• No accounts, no API keys. The payment itself is the authorization.
• Per-request pricing. Charge fractions of a cent for a single LLM completion or data lookup.
• Chain-agnostic. A server can accept USDC on Solana, USDC on Base, or any other rail it lists in the 402 response.
• Agent-native. Designed to be parsed by software, not humans.

How it relates to Solobank

Solobank’s Machine Payments Protocol is the Solana implementation of the x402 pattern. When a Solobank-equipped agent hits an MPP-protected endpoint, the SDK handles the 402 negotiation, signs a USDC transfer, and retries — typically in under a second. From the agent’s code, paying for an API call looks like any other fetch().

import { Solobank } from "@solobank/sdk";
const agent = await Solobank.create();
const result = await agent.pay({
  url: "https://api.example.com/llm",
  body: { prompt: "..." },
  maxPrice: 0.01,
});