x402 vs AP2 vs ACP: Which Agent Payment Protocol Should You Build On? (2026)
Disclosure: I work on distribution for PinkWallet, which is building an agentic payments product (mentioned once near the end, honestly, as one option in early access). Every claim about a protocol below links to that protocol's own docs, spec repo, or announcement, checked today. Short answer: Don't pick one protocol as "the" agent payment standard — pick based on what your agent is actually…
1. Paying another service per API call: For this scenario, consider either x402 or MPP. x402 is an open-source protocol that converts the HTTP 402 Payment Required status code into a feature-rich on-chain payment layer for APIs, websites, and autonomous agents. Settlement is on-chain and supported by ERC-20 tokens on Base, SPL tokens on Solana, or any Token-2022 token.
SDKs are available for TypeScript, Python, and Go. MPP, announced by Stripe in March 2026, is an open standard for machine-to-machine payments via HTTP 402, supporting stablecoins, fiat with cards, and buy now, pay later methods via Shared Payment Tokens. It also lists Bitcoin (Lightning), Solana, XRP Ledger, Stellar, Monad, and NEAR among supported rails.
Choose x402 for a stablecoin-native approach with a longer track record and Linux Foundation governance, or MPP if you need card or fiat fallback in the same integration without adding a second protocol.
2. Shopping for a person inside a chat interface: In this case, you're dealing with checkout, not raw payment settlement. ACP (Agentic Commerce Protocol) enables programmatic commerce flows between buyers, AI agents, and businesses, allowing the buyer to approve in a chat while the business remains the merchant of record. ACP can connect with any commerce backend and payments infrastructure.
First, refer to the agenticcommerce.dev spec and GitHub for the agent side, and OpenAI's commerce docs for the payment side. If building for Google's AI surfaces, consider UCP (Universal Commerce Protocol), announced by Google on January 11, 2026. UCP is an open-source standard designed for agentic commerce, compatible with AP2 for authorization.
Set up your Merchant Center account and complete a merchant interest form to integrate. Note that Google's UCP and Stripe's ACP serve different purposes, even though both operate at the merchant checkout layer.
3. Authorization record for enterprise audit or compliance: AP2 (Agent Payments Protocol) is the protocol for this scenario. AP2 uses Mandates, which are tamper-proof, cryptographically-signed digital contracts that serve as verifiable proof of a user's instructions. An Intent Mandate captures the initial instruction, while a Cart Mandate records the exact items, price, and approval when the user authorizes the cart. AP2 provides an audit trail independent of a general ledger.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
