The agentic payments landscape: x402 vs AP2, MPP, L402, and Solana Pay

Once agents can hold a wallet, every payments company wants to be the layer they pay through. The result is an alphabet soup — x402, AP2, MPP, L402 — plus older rails (Solana Pay, cards) getting pulled into the conversation. The single most useful thing to understand first: these are not all the same kind of thing. Some are settlement rails. One is an authorization framework. One is for a human scanning a QR code. Sort them by what job they do and the map gets clear fast.

The two axes that separate them

Every protocol here answers two different questions:

• Authorization — who said this payment is OK? (a human at checkout, a pre-signed mandate, a bearer credential)
• Settlement — how does the money actually move? (stablecoin on Solana, Lightning, a card network)

x402 is mostly a settlement story. AP2 is mostly an authorization story. That's why, despite the breathless "x402 vs AP2" headlines, the two are complementary — and were jointly extended to work together.

The contenders

x402 (Coinbase, now Linux Foundation). Revives HTTP 402: a server challenges, the client pays a stablecoin and retries, a facilitator verifies/settles. Settles in USDC (and EURC) on Base, Polygon, Arbitrum, World, and Solana, plus Stellar. Agent-first, no accounts. Formalized under the x402 Foundation / Linux Foundation in April 2026 with members spanning Circle, Google, Mastercard, Visa, Stripe, and the Solana Foundation. This is the broad, chain-agnostic standard — and the one with the deepest Solana support. (See our x402 deep-dive.)

AP2 — Agent Payments Protocol (Google). Not a settlement rail at all. It's an authorization framework: agents carry cryptographically signed mandates (verifiable credentials) that prove a human authorized a purchase — answering "who approved what" with a non-repudiable trail. Payment-method-agnostic (cards, bank transfers, stablecoins), an extension of Google's A2A protocol, headed toward FIDO standardization. Google, Coinbase, the Ethereum Foundation and others shipped an A2A x402 extension so crypto settles under AP2 mandates. AP2 sits above x402, not against it.

MPP — Machine Payments Protocol (Stripe + Tempo). Launched March 2026. Its headline idea is the session: an agent pre-authorizes a spending limit once, then streams granular micropayments continuously within that budget — instead of one on-chain settlement per request like x402. Settles in stablecoins on Tempo (an EVM L1), with Visa (cards) and Lightspark (Lightning) extensions. Best for continuous, metered consumption (token-by-token inference) under a budget; newer and more Tempo/Stripe-centric than x402.

L402 (Lightning Labs, formerly LSAT). Also 402-based, but settles over the Bitcoin Lightning Network and uses macaroons as bearer credentials. Its real edges: verification is a local hash check (no RPC lookup), Lightning's onion routing leaves no public on-chain footprint (privacy), and macaroons can be attenuated — a holder mints a weaker scoped credential to delegate. The cost: a Bitcoin/Lightning rail with channel liquidity to manage and a far smaller ecosystem than x402.

Solana Pay. Different category — it's for a human scanning a QR/URL at a checkout, not an agent hitting an API. No 402 challenge, no facilitator, no agent delegation; the human reviews and approves in their wallet. Native SOL or SPL transfers. Complementary to x402: human checkout vs machine API payments. (See Solana Pay — the spec.)

Cards / Stripe (traditional). The baseline everyone is routing around. A ~$0.30 fixed fee per transaction makes a $0.001 API call economically impossible — the fee dwarfs the payment. Cards also assume accounts, KYC, chargebacks, and a human present. Tellingly, Stripe itself hedged: it backs MPP and has supported x402 on Base. The fee-floor problem is precisely the gap the 402-based rails exist to close.

The map, in one table

Where Solana sits

Solana is the center of gravity for the settlement half of this map, for the same reason it always is: sub-cent fees and ~400ms finality make per-call micropayments actually work. The Solana-specific ecosystem that's grown around x402:

• Facilitators — Coinbase's hosted one, PayAI (Solana-first, gasless, reportedly the largest after Coinbase), Corbits, thirdweb, and the Rust x402-rs.
• Pay.sh — a Solana Foundation × Google Cloud API proxy built on x402 + MPP, fronting Gemini, BigQuery, and 50+ community APIs, settling in stablecoins on Solana.
• Stablecoins — USDC is the workhorse settlement token. PYUSD and USDG are present and eligible, though USDC carries the live volume today.

The honest read

Two cautions before you bet a product on any of these. First, demand is not the same as hype. x402's transaction counts look enormous (tens of millions on Solana per vendor figures), but independent coverage pegs actual dollar volume as small and flags that a large share of transactions may be artificial. Treat headline numbers as directional, not audited — build for the use case, not the chart. Second, the layers are still settling into place. The honest framing is a stack, not a winner: AP2 (or its mandates) for authorization, x402/MPP for settlement, Solana underneath when the payments are small and frequent. If you're shipping on Solana today, x402 is the pragmatic default — the broadest standard, the deepest tooling, and the one the rest of the stack is being wired to plug into.

References

• x402.org — ecosystem
• ap2-protocol.org — Agent Payments Protocol
• mpp.dev — Machine Payments Protocol
• Lightning Labs — L402
• Solana Foundation — Pay.sh with Google Cloud
• x402 — the protocol · Solana Pay — the spec

The winners here won't be decided by which acronym "beats" the others — they're solving different layers. The interesting question is which settlement rail the agents actually run on, and on that axis Solana is hard to argue with.