402 challenge
The payment instruction a server returns with anHTTP 402 response: what to pay, in what asset, to whom, on which network. The client pays and retries with proof. See HTTP 402.
Agentic payments
Autonomous agents paying for services themselves — discovering a capability mid-task, paying per call, and continuing — without a human provisioning accounts or keys first. See Agentic payments.Circle Agent Wallet
An MPC self-custody wallet for an agent, run through Circle. The signing material stays with the owner; SELAT never holds keys or funds. It is the wallet SELAT pays from.Circle Gateway
Circle’s mechanism for holding a unified USDC balance across chains and moving it instantly via deposit, burn, and mint. SELAT funds through it so an agent can pay on whatever network a merchant quotes. See Nanopayments powered by Circle Gateway.ERC-3009 (EIP-3009)
ThetransferWithAuthorization standard (ERC-3009, also referenced as EIP-3009) that lets a USDC transfer be authorized by an off-chain signature — the mechanism behind an x402 exact payment on EVM. See x402.
Federated catalog
SELAT’s merged, deduplicated index of paid services across source registries (Circle’s x402 catalog, MPP, pay.sh, Apify, and more). Discovery ranks over it. Searchable free via the Catalog MCP or the SELAT CLI.HTTP 402
The402 Payment Required status code — dormant for decades, now the foundation both x402 and MPP build on. See HTTP 402.
MPP (Machine Payments Protocol)
A multi-rail payment protocol co-authored by Stripe and Tempo, built onHTTP 402. It settles stablecoins, cards, and custom methods. See MPP on Tempo and x402 vs MPP.
Rail
A payment protocol-and-network an endpoint accepts — for example x402 (USDC on EVM/Solana) or MPP (Tempo, Stripe). The merchant chooses the rail; SELAT translates one signed shape into whichever the upstream speaks.Self-custody
The user holds the keys and the funds; no intermediary can move them. SELAT is self-custody by design — it discovers, prices, and routes, but never holds keys or balance.Tempo
The chain MPP settles its native stablecoin payments on. One of MPP’s production methods — not the only one. See MPP on Tempo.Transactability Score
SELAT’s per-endpoint reliability signal, delivered on the402 challenge: what has actually settled (success rate, paid count, last status) for an endpoint. The aggregate system is the Transactability Index. See Transactability Index.
USDC
The dollar stablecoin x402 settles in (and one of MPP’s methods). Payments in SELAT settle in USDC from the user’s Circle Agent Wallet.x402
An openHTTP 402 payment protocol from Coinbase, now under the Linux Foundation. USDC-native, on-chain, pay-per-call. See x402 and x402 vs MPP.