One rail. Four agent-payment protocols. Eleven chains.
Every chain is building its own single-protocol x402 facilitator. AlgoVoi Pay is the layer above them: one tenant-free rail that answers over x402, A2A, MPP and AP2 at once, converging on one settlement core and one offline-verifiable receipt, on whichever of eleven chains an agent already holds USDC.
01Four protocol stacks, one settlement core
A per-chain facilitator speaks one protocol. This rail answers over four, and every one settles the same way and returns the same receipt. Wire shapes below are what the live rail returns today.
Coinbase x402
GET the resource, receive a strict v2 402 with one accept per lane, pay, present the proof.
a2a-x402
An A2A message/send returns a task in the input-required state carrying the a2a-x402 payment extension.
paymentauth.org
A payment-required problem document, served as application/problem+json per RFC 9457.
Google AP2
A rail-signed CartMandate the agent verifies before any funds move.
All four hand to one settlement core → one Ed25519 receipt, verifiable offline.
02Negotiate a lane, live
The move no single-chain facilitator can make: pick the protocols and chains your agent speaks, and the rail finds the lane you share. This is what a POST to /pay/v1/negotiate returns; here it runs against the live lane set in your browser.
03Eleven mainnet lanes
An agent pays on whichever chain it already holds USDC on. The five EVM lanes take a stock EIP-3009 authorization (an off-the-shelf x402 client works); the mined-tx lanes weld the payment to its exact request through the transaction note, memo or reference.
| Chain | USDC | Binding | Stock x402 |
|---|---|---|---|
| Base | native | EIP-3009 exact | yes |
| Monad | native | EIP-3009 exact | yes |
| Polygon | native | EIP-3009 exact | yes |
| Arbitrum | native | EIP-3009 exact | yes |
| OP Mainnet | native | EIP-3009 exact | yes |
| Algorand | native | tx note weld | weld-aware |
| Solana | native | reference account | weld-aware |
| Stellar | native | MEMO_TEXT weld | weld-aware |
| Hedera | native | tx memo weld | weld-aware |
| Voi | bridged (Aramid) | tx note weld | weld-aware |
| Tempo | bridged (Stargate) | memo weld | weld-aware |
04The code your agent runs
Generated from the selected lane's live 402. The EVM lanes take a stock EIP-3009 signed authorization; the mined-tx lanes weld the challenge into the note, memo or reference.
...05One receipt, verify it offline
Whichever protocol and chain settled it, the response carries one Ed25519 JWS receipt. Paste one below: this page fetches the rail's published key once and verifies the signature entirely in your browser, no callback to the rail.
06Why not just x402
A single-chain x402 facilitator exists to keep agents on one chain, speaking one protocol. That is a fine product and the chains are funding it well. But an agent in the real world does not get to choose the counterparty's protocol or the chain its funds sit on. AlgoVoi Pay is the neutral layer above the facilitators: it meets an agent in whichever of the four protocols it speaks, settles on whichever of eleven chains it already holds USDC, and hands back one receipt anyone can verify with no AlgoVoi software. The more the ecosystem fragments into per-chain facilitators, the more that neutral layer is worth.