# payful.ai

> An independent editorial reference for AI-agent payment protocols and their real-world deployments — a living comparison matrix, per-protocol reference pages, a deployments registry, and a dated changelog.

This is an independent editorial reference. It is not affiliated with, endorsed by, or connected to any payment provider or protocol operator. Non-draft entries carry sources and a verification date; draft entries are unverified and marked as such.

## Protocols

- [x402 Payment Protocol](https://payful.ai/api/protocols/x402/md): Revives the dormant HTTP 402 status code: a server answers a request with 402 and machine-readable payment requirements, the agent signs and pays in stablecoin, a facilitator verifies and settles on-chain, and the request is retried with a payment header. Governance transferred to the vendor-neutral x402 Foundation under the Linux Foundation in 2026, with 40 founding members including Visa, Mastercard, Stripe, Adyen, and AWS.
- [Agent2Agent (A2A) Protocol](https://payful.ai/api/protocols/a2a/md): An open interoperability layer for agent-to-agent communication: it lets independent agents discover each other, exchange capabilities, and coordinate tasks. It is not a payment-execution protocol itself — payments ride on top via other protocols.
- [Agent Payments Protocol (AP2)](https://payful.ai/api/protocols/ap2/md): An authorization and governance framework for agent-initiated payments. It defines verifiable mandates that capture user intent and constraints, so an agent can transact on a user's behalf with an auditable chain of consent. Complements A2A and is rail-agnostic. Google donated AP2 to the FIDO Alliance in April 2026; v0.2 added Human-Not-Present autonomous transaction flows.
- [Machine Payments Protocol (MPP)](https://payful.ai/api/protocols/stripe-mpp/md): An open, internet-native protocol for machine and agent payments, co-authored by Stripe and Tempo. Spans both card (via Shared Payment Tokens) and stablecoin rails, settling through Stripe's existing infrastructure. The spec is open at mpp.dev; Stripe acceptance is in early access as of September 2026.
- [ERC-4337 Account Abstraction](https://payful.ai/api/protocols/erc-4337/md): An account-abstraction standard that enables programmable smart-contract wallets on Ethereum without consensus-layer changes. It is a supporting custody primitive for agent payments — session keys, spending limits, gas abstraction — not a payment protocol in its own right.
- [Pine Labs Payment Protocol (P3P)](https://payful.ai/api/protocols/p3p/md): India's first agentic payment protocol on UPI. Extends UPI's mandate framework so an AI agent can complete a payment after a single upfront user authorization, with no per-transaction human authentication. Combines UPI mandate rails, an HTTP 402 discovery layer, and the Grantex identity/audit layer.
- [Visa Trusted Agent Protocol (TAP)](https://payful.ai/api/protocols/visa-tap/md): A cryptographic trust framework for agentic commerce on the Visa network. Uses RFC 9421 HTTP Message Signatures so a Visa-approved AI agent can prove its identity, consumer authorization, and payment credentials to merchants — letting merchants distinguish legitimate buying agents from bots. Live in Europe with 30+ issuers since July 2026.
- [Mastercard Agent Pay for Machines (AP4M)](https://payful.ai/api/protocols/mc-ap4m/md): A Mastercard network service for high-frequency, low-latency machine-to-machine payments. Builds on the Agent Pay program (2025) with credentialing via Verifiable Intent, programmable permissioning, and multi-rail settlement. Launched June 2026 with 30+ partners including Stripe, Adyen, Coinbase, and Cloudflare.
- [A402 (Atomic Service Channels)](https://payful.ai/api/protocols/a402/md): A research-stage payment architecture (arXiv, Mar 2026) that binds crypto payments to verifiable service execution for machine-to-machine commerce. It is positioned explicitly as addressing x402's lack of end-to-end atomicity across execution, payment, and delivery.
- [Agentic Mobile Protocol (AMP)](https://payful.ai/api/protocols/ant-amp/md): An open-source payment protocol from Ant International for mobile interfaces — digital wallets, super apps, smart devices, and wearables — enabling AI agents to execute payments through existing mobile payment rails. Launched April 2026; global rollout across the Alipay+ ecosystem (10 wallets, 7 acquirers) announced September 2026. Ant International, Mastercard, and Visa are collaborating on a Know-Your-Agent (KYA) interoperability framework through BuildFin.ai (MAS).
- [Agentic Commerce Protocol (ACP)](https://payful.ai/api/protocols/acp/md): An open interaction model and standard for AI agent–driven consumer purchases, co-developed by OpenAI and Stripe. Defines a checkout session lifecycle (create, update, complete, cancel) so agents can discover products, manage carts, and complete purchases on behalf of consumers with human approval at payment. Powers ChatGPT's Instant Checkout and is adopted by merchants including Etsy, Target, and Sephora. Still in beta as of September 2026. (unverified draft)
- [Universal Commerce Protocol (UCP)](https://payful.ai/api/protocols/ucp/md): An open-source standard from Google for agentic commerce across the full shopping journey — discovery, cart, checkout, and post-purchase support. Co-developed with Shopify, Etsy, Wayfair, Target, and Walmart, and endorsed by 20+ ecosystem partners including Adyen, Mastercard, Stripe, and Visa. Compatible with A2A, AP2, and MCP. Powers checkout on Google AI Mode in Search and Gemini. Live since January 2026; expanded globally with cart, catalog, and identity-linking capabilities. (unverified draft)
- [NPCI Unified Agent Protocol (UAP)](https://payful.ai/api/protocols/npci-uap/md): A reported national framework from India's NPCI to let AI agents execute small-ticket UPI payments using UPI Circle (delegated authority) and Reserve Pay (pre-blocked funds), with spending limits, identity checks, and audit trails. NPCI deferred the expected launch at Global Fintech Fest (September 8–11, 2026) pending regulatory review. At GFF on September 10, NPCI's chairman publicly described the protocol work for the first time, stating that AI agents may read intent but authentication and settlement must remain deterministic and auditable. No public specification has been released. (unverified draft)

## Deployments

- CoinGecko x402 Endpoints (CoinGecko, x402, live) — https://www.coingecko.com/
- Coinbase Agent.market (Coinbase, x402, live) — https://docs.cdp.coinbase.com/x402
- Cloudflare Agents SDK + Monetization Gateway (Cloudflare, x402, live) — https://developers.cloudflare.com/agents/tools/payments/x402/charge-for-http-content/
- Stripe Machine Payments (Stripe, stripe-mpp, live) — https://docs.stripe.com/payments/machine
- Circle Wallets + x402 Reference Workflow (Circle, x402, live) — https://www.circle.com/
- AP2 via PayPal (PayPal (with Google), ap2, pilot) — https://cloud.google.com/blog/products/ai-machine-learning/announcing-agents-to-payments-ap2-protocol
- ZeroClick (ZeroClick, x402, live) — https://zeroclick.ai/
- Polygon x402 Facilitators (Polygon, x402, live) — https://docs.polygon.technology/payment-services/agentic-payments/x402/intro
- X Pay x402 Gateway (X-Pay Technologies, x402, live)
- Mastercard Agent Connect (Mastercard, mc-ap4m, live) — https://thepaypers.com/payments/news/mastercard-launches-agent-connect-for-agentic-commerce
- Circle x402 Facilitator Service on Arc (Circle, x402, live) — https://www.circle.com/pressroom/circle-launches-arc-mainnet-an-economic-operating-system-for-the-internet
- Alchemy AgentCard + Mastercard Agent Pay (Alchemy, mc-ap4m, live) — https://agentcard.ai/

## Data

- [Full registry (JSON)](https://payful.ai/api/registry)
- [Comparison matrix](https://payful.ai/compare)
- [Deployments](https://payful.ai/deployments)
- [Changelog](https://payful.ai/changelog)
- [Sitemap](https://payful.ai/sitemap.xml)