You probably forgot about HTTP 402 Payment Required nestling between HTTP 401 Unauthorised, and 403 Access forbidden. We did.
But now it’s getting resurrected for the crypto age and it may be the payment rails we’ve been waiting for.
x402 is an open-source payment protocol developed by Coinbase in 2025, designed to enable instant, automated stablecoin payments directly over HTTP by activating the long-dormant HTTP 402 “Payment Required” status code. It serves as a chain-agnostic standard that allows AI agents, applications, and autonomous systems to send and receive money without human intervention, registrations, or complex integrations. So what are the key features?
- HTTP-Native Integration: Builds on existing web infrastructure for seamless API monetization and resource access, supporting payments via simple HTTP requests.
- AI and Agent Focus: Optimized for the “agentic economy,” enabling AI-driven transactions, on-chain settlements, and interoperability with ecosystems like Google’s Agent Payments Protocol (AP2).
- Ecosystem Applications: Powers tools for AI research platforms, DeFi execution, and agent commerce, with implementations on chains like Base, Avalanche, Solana, and BSC.
- Security and Scalability: Includes verifiable computations and cryptographic proofs for secure, decentralised operations.
x402 addresses a 25-year gap in internet payments by making them native to the web, fostering autonomous economies where agents can transact fluidly across Web2 and Web3. It’s gaining traction in AI and crypto communities, with Masumi taking the lead for Cardano.
— Masumi (@MasumiNetwork) October 27, 2025
Check out their test implementation here.
This one could be the first killer app for crypto beyond store of value.