Agentic Payment Protocols: x402 vs AP2 vs MPP vs ACP
Four agentic payment protocols—x402, AP2, MPP, and ACP—address distinct layers of transactions, with none covering all needs. Institutions are supporting multiple standards simultaneously.
x402 revives HTTP 402 to enable instant, account-free payments for machine-to-machine transactions such as API calls and data access. The protocol, now managed by the x402 Foundation with 40 members including AWS, Circle, and Visa, recorded over 100 million transactions on Base by Q1 2026, primarily for larger payments rather than microtransactions. Its design eliminates the need for subscriptions or checkout pages, focusing on stablecoin settlements within a single request cycle.
AP2, launched in September 2025 with partners like Mastercard and PayPal, operates at the permission layer by encoding purchases as three cryptographically signed mandates—Intent, Cart, and Payment—carried as verifiable credentials. The protocol does not move funds but provides audit trails for disputes and compliance in agent-driven transactions across cards, bank transfers, and stablecoins. Its rail-agnostic structure ensures compatibility with existing payment rails without altering settlement processes.
The Machine Payments Protocol (MPP), introduced in March 2026 by Stripe and Tempo, introduces session-based pre-authorization to enable continuous, granular micropayments without onchain transactions per interaction. MPP supports stablecoins natively on Tempo, card payments via Visa, and Bitcoin over the Lightning Network. Over 100 services, including model providers and compute platforms, were listed at launch, demonstrating its adaptability across diverse use cases and payment rails.
The Agentic Commerce Protocol (ACP), co-developed by OpenAI and Stripe and open-sourced in September 2025, standardizes checkout flows between AI agents and merchants by defining operations for creating, updating, completing, and canceling transactions. ACP focuses on consumer purchases of physical and digital goods using fiat rails, while leaving wallet security, policy enforcement, and compliance reporting to underlying infrastructure layers. Fireblocks has contributed a security extension to x402 to address these gaps.