AI Agents Just Activated HTTP's Forgotten Payment Code

x402 is an open standard that enables AI agents to instantly pay for APIs and services directly over HTTP using stablecoins, eliminating the need for accounts, API keys, or human intervention. Launched by Coinbase in May 2025, it repurposes the 402 Payment Required status code—reserved since 1996—to create a machine-first payment layer. This fundamentally transforms how autonomous software discovers and purchases services, enabling agents to execute thousands of micropayments daily without human oversight.