# Mandates and Machines: AP2, ACP, x402 and the Payment Protocol Contest

> Six agent payment protocols launched in twelve months; this comparison dates each one, tabulates scope, settlement rails and governance, and argues that the signed mandate is the primitive that decides the contest.

- Canonical: https://aiagentinfra.com/articles/agent-payment-protocols-ap2-acp-x402-mpp
- Author: Ryan Elliott Dennis
- Category: Protocols & Interoperability
- Kind: Reference article
- Last verified: 2026-09-04
- Keywords: agent payments protocol, AP2, Agentic Commerce Protocol, x402, Machine Payments Protocol, Trusted Agent Protocol, agent payment protocols compared, HTTP 402

> "Stripe is building the economic infrastructure for AI." — Will Gaybrick, President of technology and business, Stripe (Stripe newsroom, Sept. 29, 2025)

One million merchants. That was the number Stripe attached to the Agentic Commerce Protocol on Sept. 29, 2025, when it launched Instant Checkout inside ChatGPT with US Etsy sellers live and more than a million Shopify merchants, Glossier, Vuori, Spanx and SKIMS among them, "coming soon." Will Gaybrick, Stripe's president of technology and business, framed the launch in one line: "Stripe is building the economic infrastructure for AI." McKinsey's QuantumBlack unit supplied the ceiling on Jan. 28, 2026, projecting that agents could mediate $3 trillion to $5 trillion of global consumer commerce by 2030. Between the merchant count and the trillions sit six agent payment protocols launched in twelve months, each with a different answer to the same question: when software spends money, what record proves a human allowed it? This article dates the six, tabulates their scope, settlement rails and governance, and argues that the mandate, the signed and scoped authorization, is the primitive on which the contest turns.

## Six Standards in Twelve Months: The Field, Dated

Coinbase moved first with x402 on May 6, 2025, reviving the HTTP 402 status code for stablecoin payments between machines, with AWS, Anthropic, Circle and NEAR as launch partners. Google announced the Agent Payments Protocol, AP2, on Sept. 16, 2025, with more than 60 organizations. Stripe and OpenAI released ACP on Sept. 29, 2025. Visa introduced its Trusted Agent Protocol in October 2025 with more than 10 partners. Stripe returned on March 18, 2026, with the Machine Payments Protocol, co-authored with Tempo. Mastercard closed the sequence on June 10, 2026, with Agent Pay for Machines and more than 30 participants. Two of the six come from card networks, two from Stripe, one from Google and one from a crypto exchange, and the overlap among their participant lists, with Coinbase, Cloudflare, Stripe and Tempo appearing inside Mastercard's coalition, shows an industry hedging every rail at once.

| Protocol | Owner and governance | Scope | Settlement rails | Launched | Adoption evidence (date) |
|---|---|---|---|---|---|
| x402 | Coinbase; x402 Foundation with Cloudflare, Linux Foundation-hosted | HTTP 402 pay-per-request between machines | Stablecoins, chiefly USDC on Base | May 6, 2025 | 100M+ transactions on Base through Q1 2026 (Chainalysis, June 3, 2026); settlement volume −93% year to date (CCN, Aug. 13, 2026) |
| AP2 | Google with 60+ organizations | Intent and Cart Mandates; extends A2A and MCP | Cards first; stablecoins via the A2A x402 extension | Sept. 16, 2025 | v0.2.0 in April 2026; 60+ members incl. PayPal, Mastercard, American Express (TNW, May 19, 2026) |
| ACP | OpenAI and Stripe, open standard | Checkout inside chat via Shared Payment Token | Cards through Stripe | Sept. 29, 2025 | Etsy live; 1M+ Shopify merchants pending; PayPal adopted in Oct. 2025 (Digital Commerce 360, Feb. 16, 2026) |
| Trusted Agent Protocol | Visa | Agent recognition at merchant checkout | Visa credentials | Oct. 2025 | 10+ partners; hundreds of agentic transactions and 100+ partners (Visa, Dec. 18, 2025) |
| MPP | Stripe and Tempo, open standard | Machine payments beyond per-purchase human approval | Stablecoins via Tempo; cards and BNPL via Shared Payment Tokens | March 18, 2026 | Early users Browserbase, Parallel Web Systems, PostalForm, Prospect Butcher Co. (Stripe, March 18, 2026) |
| Agent Pay for Machines | Mastercard | Credentialing, spend limits, micro-transactions | Cards, accounts and stablecoins | June 10, 2026 | 30+ participants; permissions recorded on Polygon, Solana and Base (CoinDesk, June 10, 2026) |

## Mandates as the Accountability Primitive: AP2's Intent and Cart

AP2 is the protocol that names the problem. Announced on the Google Cloud blog by Stavan Parikh and Rao Surapaneni on Sept. 16, 2025, it extends A2A and MCP with two signed objects, an Intent Mandate that records what the user asked for and a Cart Mandate that records what the agent assembled, both signed with verifiable credentials, which gives merchant, issuer and network a record from which authorization can be reconstructed. Its coalition at launch included Mastercard, American Express, PayPal, Adyen, Ant International, UnionPay, JCB, Worldpay, Coinbase, Revolut, Salesforce, ServiceNow, Intuit, Etsy, Adobe, Shopee, Accenture, Deloitte, PwC, Dell, Okta, 1Password and Mysten Labs, and an A2A x402 extension built with Coinbase, the Ethereum Foundation and MetaMask gave it a stablecoin path from day one. By April 2026 the specification had reached v0.2.0, and at Google I/O on May 19, 2026, The Next Web counted 60-plus members and described mandates for purchases completed while the human is away from the session; the same report described a donation of AP2 to the FIDO Alliance, a step this journal has yet to confirm against a Google or FIDO primary source. The protocol's site in September 2026 still describes cards as the live rail with real-time transfers and digital currencies following. Mandates are the durable idea. A payment that carries its own authorization record can be disputed, audited and revoked, which is what every other protocol in the table is now retrofitting.

## Checkout in the Chat: ACP, Shared Payment Tokens and a Million Merchants

ACP solves a narrower problem with a sharper primitive. Stripe and OpenAI codeveloped the standard so that a conversation can end in a purchase, and Stripe's Shared Payment Token, scoped to a specific merchant and cart total, lets ChatGPT initiate a payment while the buyer's card credentials stay with Stripe. Etsy's US sellers were live on Sept. 29, 2025; the million-plus Shopify merchants were promised; PayPal adopted ACP in October 2025, per Digital Commerce 360's Feb. 16, 2026, account of OpenAI's expanding commerce push. The scoping is the accountability mechanism: a token that works for one merchant and one amount is a mandate in miniature, held by Stripe on the buyer's behalf, with the dispute path running through card rules. Note the acronym collision. Virtuals Protocol calls its on-chain escrow sequence the Agent Commerce Protocol and IBM shipped an Agent Communication Protocol, so "ACP" now resolves three ways, and buyers evaluating the Stripe standard should check which one a vendor means.

## HTTP 402, Revived: x402 and the Machine-to-Machine Tier

x402 addresses the tier beneath checkout, where an agent pays a server for a page, a dataset, an API call or a tool invocation in fractions of a cent. Coinbase launched it on May 6, 2025, and Cloudflare joined on Sept. 23, 2025, to form the x402 Foundation, adding x402 to its Agents SDK and MCP integrations, proposing a deferred-payment scheme and linking the protocol to pay-per-crawl. Adoption arrived fast and then thinned. Chainalysis reported on June 3, 2026, that x402 transactions on Base went from near zero in mid-2025 to well over 100 million cumulative through the first quarter of 2026, with a single week in the fourth quarter of 2025 up more than 10,000% on the pay-to-mint token PING. CCN's Giuseppe Ciccomascolo reported on Aug. 13, 2026, citing Helios Analytics, that daily settlement volume had fallen 93% year to date, from a late-2025 level that repeatedly approached $800,000 to a seven-day average near $41,800, while Ripple joined the Linux Foundation-hosted foundation in July and Cloudflare launched its Monetization Gateway on July 1 to charge for web pages, APIs, datasets and Model Context Protocol tools. The protocol's weakness is the mirror of its strength: a bearer payment with zero mandate attached settles instantly and leaves the chain as its sole auditor. Its governance is now the broadest of the six. Volume, by contrast, is the most volatile.

## Cards Answer: Visa's Trusted Agent Protocol and Mastercard's Machines

The networks responded with recognition and credentials. Visa's Trusted Agent Protocol, introduced in October 2025 with more than 10 partners, lets a merchant distinguish an authorized agent from a bot at checkout. The company's Dec. 18, 2025, release reported "hundreds" of controlled agentic transactions, more than 100 ecosystem partners, more than 30 building in its sandbox, more than 20 agents integrating, US pilots with Skyfire, Nekuda, PayOS and Ramp, and a finding that 47% of US shoppers use AI for shopping tasks. Mastercard went further on June 10, 2026. Agent Pay for Machines credentials agents under a Verifiable Intent scheme, enforces programmatic spending limits, supports high-frequency micro-transactions and settles across cards, accounts and stablecoins; CoinDesk's Helene Braun reported the same day that permissions and credentials are recorded initially on Polygon, Solana and Base and that the product targets the HTTP 402 declines agents already generate at merchants with zero way to accept them. Stephanie Cohen, Cloudflare's chief strategy officer, said in the Mastercard release that the partnership connects Cloudflare's developer and security platform with Mastercard's payments infrastructure for machine-to-machine commerce. Each network has built a mandate under another name, Visa's inside the credential and Mastercard's inside Verifiable Intent, and each has chosen to record it where counterparties can check it.

## MPP and Tempo: Stripe's Second Standard

Stripe's second protocol shows where the company thinks the boundary lies. Jeff Weinstein and Steve Kaliski introduced the Machine Payments Protocol on March 18, 2026, as an open standard co-authored with Tempo, the stablecoin network Stripe developed with Paradigm, for payments an agent completes on its own within limits a human set in advance. Stablecoins settle through Tempo; cards and buy-now-pay-later settle through the same Shared Payment Tokens that power ACP; early users named at launch were Browserbase, Parallel Web Systems, PostalForm and Prospect Butcher Co. Stripe therefore holds one protocol for humans buying in chat and one for machines buying from machines, joined by a single token primitive, and it sits inside Mastercard's coalition as well. Forrester's Emily Pfeiffer offered the corrective on May 28, 2026: most agentic-commerce value in mid-2026 comes from comparison and guidance, hard adoption numbers are scarce, and most consumers still insist on direct oversight before an agent completes a purchase. The protocols are ahead of the behavior they are designed to govern.

## Who Holds the Mandate: Liability, Disputes and the Accountability Gap

Read the table by its fourth column and the six protocols sort into two families: those that settle on cards and inherit a century of dispute rules, and those that settle on stablecoins and inherit finality. Sort it by scope and the grouping changes, into protocols that carry a mandate, AP2 explicitly, ACP and MPP through token scoping, Visa and Mastercard through credentials, and one, x402, that carries a payment and leaves authorization to whoever built the agent. McKinsey's automation curve, published Jan. 28, 2026, runs from Programmed Convenience at level zero to Networked Autonomy at level five, where agents negotiate with agents, and its authors frame the objective as optimal delegation over maximal autonomy. Delegation requires a record. The record is the mandate. Whichever protocol makes that record cheapest to create, easiest to verify and hardest to forge will carry the volume when the volume arrives, and on the evidence to Sept. 4, 2026, that is a contest the card networks and Google are fighting with signatures while x402's foundation, Ripple and Cloudflare included, works to add them after the fact.

## What to Watch

Five signals will reorder the table before the year ends. The Shopify million: Stripe promised it on Sept. 29, 2025, and a disclosed count of merchants transacting through ACP would convert the launch figure into an adoption figure. AP2's rails: the site still lists cards as live, and the first production stablecoin mandate through the A2A x402 extension would make the protocol multi-rail in fact. x402's reconciliation: Helios's 93% decline and Chainalysis's 100 million transactions describe different quantities, and the Cloudflare Monetization Gateway is the demand engine that could move both. Mastercard's first disclosed stablecoin settlement share under Agent Pay for Machines would show whether a permissioned multi-rail network absorbs the open rail. Visa's move from hundreds of transactions to thousands would date the moment agentic checkout became routine. Mandates first. Volume follows the record.

## By the numbers

- Shopify merchants slated for Instant Checkout: 1M+ — Announced as coming soon on Sept. 29, 2025, with US Etsy sellers live at launch [1]
- Agent-mediated consumer commerce by 2030: $3–5T — McKinsey QuantumBlack projection, Jan. 28, 2026 [11]
- AP2 launch coalition: 60+ organizations — Google Cloud announcement, Sept. 16, 2025; v0.2.0 followed in April 2026 [2]
- x402 settlement volume, year to date: −93% — Helios Analytics data reported by CCN, Aug. 13, 2026, after 100M+ transactions on Base through Q1 2026 [6]
- Agent Pay for Machines participants: 30+ — Mastercard launch, June 10, 2026; multi-rail settlement across cards, accounts and stablecoins [9]

## Sources

1. Stripe, "Stripe powers Instant Checkout in ChatGPT and releases Agentic Commerce Protocol codeveloped with OpenAI," Stripe newsroom, Sept. 29, 2025. https://stripe.com/newsroom/news/stripe-openai-instant-checkout
2. Stavan Parikh and Rao Surapaneni, "Announcing Agent Payments Protocol (AP2)," Google Cloud blog, Sept. 16, 2025. https://cloud.google.com/blog/products/ai-machine-learning/announcing-agents-to-payments-ap2-protocol
3. Coinbase Developer Platform, "x402: Introducing the internet-native payment protocol," Coinbase, May 6, 2025. https://www.coinbase.com/developer-platform/discover/launches/x402
4. Cloudflare, "Launching the x402 Foundation with Coinbase, and support for x402 transactions," Cloudflare blog, Sept. 23, 2025. https://blog.cloudflare.com/x402/
5. Chainalysis, "Inside x402: 100M Agentic Payments on Base," Chainalysis blog, June 3, 2026. https://www.chainalysis.com/blog/x402-agentic-payments-adoption/
6. Giuseppe Ciccomascolo, "x402 Settlement Volume Plunges 93% YTD, but Cloudflare Could Revive AI Agent Payments," CCN via Yahoo Finance, Aug. 13, 2026. https://finance.yahoo.com/markets/crypto/articles/x402-settlement-volume-plunges-93-105710906.html
7. Jeff Weinstein and Steve Kaliski, "Introducing the Machine Payments Protocol," Stripe blog, March 18, 2026. https://stripe.com/blog/machine-payments-protocol
8. Visa, "Visa and Partners Complete Secure AI Transactions, Setting the Stage for Mainstream Adoption in 2026," Visa investor relations, Dec. 18, 2025. https://investor.visa.com/news/news-details/2025/Visa-and-Partners-Complete-Secure-AI-Transactions-Setting-the-Stage-for-Mainstream-Adoption-in-2026/default.aspx
9. Mastercard, "Mastercard Launches Agent Pay for Machines," Mastercard newsroom, June 10, 2026. https://www.mastercard.com/us/en/news-and-trends/press/2026/june/mastercard-launches-agent-pay-for-machines.html
10. Helene Braun, "Mastercard Prepares for a Future Where AI Agents Make Payments With Latest Introduction," CoinDesk, June 10, 2026. https://www.coindesk.com/business/2026/06/10/mastercard-prepares-for-a-future-where-ai-agents-make-payments-with-latest-introduction
11. Mahajan, Mayer, Schumacher and Roberts, "The automation curve in agentic commerce," McKinsey QuantumBlack, Jan. 28, 2026. https://www.mckinsey.com/capabilities/quantumblack/our-insights/the-automation-curve-in-agentic-commerce
12. "Google Universal Cart, AP2 and UCP at I/O 2026," The Next Web, May 19, 2026. https://thenextweb.com/news/google-universal-cart-agent-payments-shopping-io-2026
13. Emily Pfeiffer, "The State of Agentic Commerce in Mid-2026," Forrester, May 28, 2026. https://www.forrester.com/blogs/the-state-of-agentic-commerce-in-mid-2026/
14. "OpenAI expands agentic commerce push," Digital Commerce 360, Feb. 16, 2026. https://www.digitalcommerce360.com/2026/02/16/openai-expands-agentic-commerce-push/