Circle Nanopayments runs on x402 — what this means for AI agents that pay for data

Last week Circle shipped Nanopayments. The interesting part isn't the feature — it's what they built it on. They chose x402. Not a proprietary Circle API. Not a closed payment protocol. They built on the open HTTP standard that Cloudflare, Coinbase, and the x402 Foundation have been developing. That's a meaningful signal if you're building agents that buy things. The agent payment rail race is settling Quick recap of where things stand: x402 — open HTTP standard. A server responds to an unauthorized request with 402 Payment Required , and the body tells the client exactly what to pay, to whom, and how. The client pays in USDC on Base, includes a signed payment proof in an X-Payment header, and gets the data. No API keys. No billing dashboard. The payment is the auth. Stripe Tempo — enterprise billing for AI platforms. Designed for SaaS companies charging humans for AI features. Not designed for agent-to-agent micropayments at sub-cent scale. Circle Nanopayments — just launched, built o