Agent payment protocols compared: x402, L402, MPP and Cashu NUT-24
When an AI agent hits an HTTP 402 paywall, four protocols show up across our live probes: x402 (USDC), L402 (Bitcoin Lightning), MPP (Machine Payments Protocol), and Cashu NUT-24 (bearer ecash). Every count and price below is computed from our checked datasets as of 2026-10-24.
live HTTP 402 APIs compared
536
367 x402 · 132 L402 · 36 MPP · 1 Cashu NUT-24
cheapest USD call
$0.0001
Object Storage: List objects (MPP)
free browser sandbox
21 test sats
try a real NUT-24 HTTP 402 flow at /try402 with zero real money
Side-by-side protocol comparison
| Dimension | x402 | L402 | MPP | Cashu (NUT-24) |
|---|---|---|---|---|
| Primary asset & chain | USDC on Base / Solana | Bitcoin over Lightning (sats) | USDC.e on Tempo or Lightning BOLT11 | Cashu ecash tokens (sats, custodial mints) |
| HTTP 402 challenge header | PAYMENT-REQUIRED (v2) or JSON accepts[] | WWW-Authenticate: L402 macaroon="…", invoice="lnbc…" | WWW-Authenticate: Payment realm="…", method="tempo|lightning", request="…" | X-Cashu: <creqA…> payment request |
| Retry / proof header | PAYMENT-SIGNATURE (v2) or X-PAYMENT (v1) | Authorization: L402 <macaroon>:<preimage> | Authorization: Payment <credential> | X-Cashu: <cashuB…> ecash token |
| Live 402 APIs in our index | 367 | 132 | 36 | 1 live NUT-24 (15 Cashu API/middleware entries total) |
| Cheapest live call | $0.0001 · x402wrapper | $0.0008 (1 sat) · Loop Gateway | $0.0001 · Object Storage: List objects | 42 sat · Clawtar demo (clawtar.cashutools.dev) (+ free 21 test sat sandbox at /try402) |
| Median price per call | $0.010 | $0.0082 | $0.0051 | 42 sat |
| YES services in /payments | 331 | 11 (plus 16 on lightning) | 29 | 41 verified in /cashu |
| Wallets supporting rail | 54 | 123 Lightning (3 list l402 explicitly) | 70 stablecoin / 123 Lightning | 56 ecash wallets in leaderboard |
| MCP servers supporting rail | 64 | 8 l402 / 15 lightning | 7 | 5 in /cashu |
| Custody & trust model | Self-custodial or delegated EVM/Solana wallet; EIP-3009 off-chain signature | Self-custodial or NWC Lightning wallet; cryptographic payment preimage | Tempo wallet or Lightning preimage per challenge method | Every Cashu mint is custodial: operator holds the bitcoin (small amounts only) |
All API prices come from one unpaid HTTP 402 probe per endpoint. Sat prices are converted at $0.00081513 per sat (ratio of price_usd/price_sats in 402 Index API responses on 2026-10-15 (approximate, used only for sorting)) for USD comparison.
When builders pick each protocol
- x402 (USDC on Base / Solana): Largest catalog of pay-per-call APIs (367 live endpoints, median $0.010). Fits agents that already hold USDC or use EVM/Solana toolkits. Guide: /how-agents-pay-with-x402.
- L402 (Bitcoin Lightning + macaroon): 132 live endpoints starting at 1 sats ($0.0008). Uses a BOLT11 invoice plus a cryptographic preimage proof with no on-chain gas or token approvals. Guide: /can-ai-agents-pay-with-lightning and /x402-vs-l402.
- MPP (Machine Payments Protocol): 36 live endpoints using standard HTTP
WWW-Authenticate: Paymentchallenges (settled in USDC.e on Tempo or over Lightning). Browse: /apis?p=mpp. - Cashu NUT-24 (bearer ecash over HTTP 402): Bearer token sent directly in
X-Cashuwith no wallet signature or network lookup from the client. Every Cashu mint is custodial and early-stage, so use small amounts only. Browse /cashu or test it free in your browser at /try402.
Plain-English meanings
- HTTP 402
- “Payment Required”: a web status code a server sends when a request has to be paid for first.
- x402
- The same pay-first idea for APIs, but paid in USDC (a dollar stablecoin) instead of Bitcoin.
- L402
- A way for an API to say “pay first”: it replies with a Lightning invoice, the agent pays a few sats, then gets its answer.
- MPP
- Machine Payments Protocol: an open standard that lets agents pay for web services per request, with stablecoins or other payment methods.
- Cashu
- An ecash system for Bitcoin: you deposit sats with a mint and get back bearer tokens you can send like a file. Fast and cheap, but you must trust the mint.
- NUT-24
- The Cashu standard for paying over HTTP 402: the server answers 402 with an X-Cashu payment request, then the agent retries with a Cashu token in the X-Cashu header.
- Lightning
- Bitcoin’s fast, cheap payment layer: payments settle in seconds and can cost a fraction of a cent.
- USDC
- A digital dollar: a crypto token meant to always be worth one US dollar.
Data as of 2026-10-24. How we check: /method.