Several schemes let software pay for resources. They differ in transport, settlement rail, and whether they price a single HTTP request or orchestrate a multi-step purchase. Here is how the main ones line up.
Revives HTTP 402: the server returns payment requirements inline, the client signs a stablecoin authorization (USDC on Base or Solana), and retries. Per-request, HTTP-native, no account. Best for paying for individual API calls — which is what 2s implements.
An earlier HTTP-402-style scheme tied to Bitcoin Lightning, using macaroon tokens plus a Lightning invoice. Also per-request, but settles over Lightning rather than an EVM/SVM stablecoin transfer, and carries a token you present on subsequent calls.
A newer class focused on authorizing an agent to make purchases on a user’s behalf — mandates, intents, and multi-party flows — rather than pricing one HTTP request. They operate at a higher level than x402 and can, in principle, sit above a per-call rail like x402.
Call a live x402 API right now — no signup.
Browse the full endpoint directory, grab the quickstart, or read the llms.txt manifest. Every endpoint is keyless and pay-per-call.