Do I have to choose between x402 and MPP?

No. The two protocols are not mutually exclusive: a 402 response can carry both header sets side by side. AsterPay's API accepts both x402 and MPP on every paid endpoint — crypto-native agents pay USDC via x402, while agents wired to Stripe-style fiat infrastructure pay via MPP. Supporting both roughly doubles the addressable agent population for zero extra integration work when you use a facilitator that handles both.

Which protocol do AI agents actually use today?

x402 has the larger live ecosystem today — Coinbase's facilitator, the x402 Bazaar marketplace, and thousands of indexed endpoints (see x402scan and the Open 402 Directory). MPP is newer but backed by Stripe's merchant network and the Tempo blockchain consortium, so fiat-side adoption is expected to grow quickly. Agent-facing APIs that want maximum reach advertise both.

How does EUR settlement work with x402 and MPP?

With x402 the agent pays USDC on-chain; a facilitator like AsterPay converts it and pushes a SEPA Instant payout, so the merchant receives EUR in their bank account in under 10 seconds. With MPP the payment already starts on fiat rails, and settlement follows the PSP's payout schedule. AsterPay normalizes both flows: whichever protocol the agent pays with, the merchant gets EUR to their IBAN with one integration.

Can one API endpoint accept both x402 and MPP?

Yes. The HTTP 402 response simply lists every payment option the server accepts — the x402 accepts array and the MPP method advertisement can coexist in one response. The agent inspects the options, picks the rail it holds funds on, and retries the request with the corresponding payment proof. AsterPay runs this dual-protocol pattern in production on every paid endpoint at x402.asterpay.io.

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x402 vs MPP — which agent payment protocol should you support?

By Petteri, Co-founder of AsterPay · Last updated 9 June 2026 · 5 min read

Answer Both are HTTP 402 payment protocols for AI agents, but they settle on different rails. x402 (Coinbase) settles in stablecoins on-chain — typically USDC on Base. MPP, the Machine Payments Protocol (an open standard from Stripe and Tempo), settles over fiat and PSP rails. They are not mutually exclusive: a single 402 response can advertise both, and dual-protocol facilitators like AsterPay accept either on every paid endpoint.

The 30-second history

x402 revived the dormant HTTP 402 "Payment Required" status code in 2025 as a machine-payable standard: the server replies 402 with an accepts array describing how to pay (asset, chain, amount, recipient), the agent signs an EIP-3009 transferWithAuthorization, and a facilitator verifies and settles it on-chain. Coinbase published the reference implementation and runs the default facilitator.

MPP (Machine Payments Protocol) arrived from the fiat side: an open standard from Stripe and the Tempo ecosystem that uses the same 402 handshake but replaces on-chain transfers with payment tokens that clear over conventional PSP infrastructure. An agent with access to a funded MPP wallet or card-rail backing can pay without touching a blockchain.

Side-by-side comparison

Dimension	x402	MPP
Origin	Coinbase (open spec)	Stripe + Tempo (open spec)
Settlement rail	On-chain — USDC on Base (also ETH L2s, Solana)	Fiat / PSP rails, payment tokens
Typical asset	USDC, EURC stablecoins	USD / fiat balances
Finality	~2–3 s on Base	PSP authorization, payout per schedule
Micropayment floor	Sub-cent viable ($0.001 works)	PSP minimums apply
Agent wallet needed	Crypto wallet + USDC balance	MPP-enabled account (e.g. Stripe-issued)
Chargebacks	None (refund protocols layer on top)	PSP dispute rules
Live ecosystem today	x402 Bazaar, x402scan, thousands of endpoints	Growing via Stripe merchant network

Why "both" is the right answer for API sellers

The protocols compete for the same HTTP handshake but serve different agent populations. Crypto-native agents hold USDC and pay via x402 today. Enterprise agents wired into Stripe-style billing will arrive with MPP credentials. Since one 402 response can carry both header sets side by side, advertising both costs nothing and roughly doubles your addressable demand.

AsterPay runs this dual-protocol pattern in production: every paid endpoint at x402.asterpay.io accepts both x402 and MPP, and the MPP method advertisement is published alongside the x402 discovery document.

What about EUR settlement?

Neither protocol pays your European suppliers in euros by itself. With x402 the merchant ends up holding USDC; with MPP the funds sit at the PSP. AsterPay closes the last mile for both: USDC from x402 payments is converted and pushed to the merchant's IBAN via SEPA Instant in under 10 seconds, and MPP-side flows are normalized into the same EUR payout pipeline. One integration, two protocols, euros in the bank.

Decision guide

Selling API calls to AI agents today? → Support x402 first (largest live agent population), add MPP via a dual-protocol facilitator.
Enterprise customers on Stripe billing? → MPP support future-proofs you; you keep one 402 handshake for both.
European merchant who needs EUR, not USDC? → Use a facilitator with native EUR settlement (AsterPay is the only one combining dual-protocol acceptance with SEPA Instant payout and KYA trust scoring).
Building an agent that pays? → Read the 402 response's options and support whichever rails your treasury holds; x402 needs a funded USDC wallet, MPP needs an MPP-enabled account.