The Machine Payments Protocol (MPP): An Updated Guide

What MPP is

The Machine Payments Protocol (MPP) is an open standard that lets software agents pay for things over the web without a human filling in a checkout form. Stripe and Tempo launched it together, and it works inside the normal request and response cycle that every website and API already uses.

The problem it solves is simple. Pricing pages, plan pickers and card forms were built for people. An AI agent that needs to buy one API call, one dataset or one browser session has no good way through them. MPP gives the agent a direct route: ask for the resource, get told the price, pay, and receive it.

Six months after its March 2026 launch, MPP has moved from an announcement to a working network with real, if still small, usage. This post covers how it works, what has changed since launch, and what to watch next.

How it works

MPP builds on HTTP status code 402, Payment Required. The web has reserved that code for payments since the 1990s, but it was rarely used. MPP gives it a clear set of rules, and the whole exchange happens inside one request cycle with no redirect or checkout page.

An agent asks for a paid resource. The service answers with a 402 and a challenge that states the price and the payment methods it accepts. The agent pays, then sends the request again with proof of payment. The service checks the payment and returns the resource with a receipt.

The resource can be almost anything reachable over the web: an API endpoint, a Model Context Protocol (MCP) tool, a file or a page. Charges can be very small. The launch materials cite amounts as low as 0.01 USDC, which makes per-call pricing workable where a card fee would swallow the whole payment.

For businesses on Stripe, setup takes a few lines of code with the PaymentIntents API. Stripe creates a deposit address on Tempo, converts incoming stablecoins, and settles the money into the business’s normal balance in its usual currency. Stripe can also cover the small Tempo network fee, so the business does not need to run its own crypto wallet.

Payment methods and sessions

MPP does not care how the money moves. The spec keeps the core protocol separate from payment methods, so new rails can plug in without changing how agents and services talk. The main options today are:

Stablecoins such as USDC on Tempo, a payments blockchain incubated by Stripe and backed by Paradigm.
Cards and buy now, pay later through Stripe, using Shared Payment Tokens that cap how much an agent can spend and for how long.
Card payments built on Visa’s MPP specification and SDK.
Bitcoin over the Lightning Network, added by Lightspark.

The spec also defines payment types. A charge is one payment for one request. A session lets an agent deposit funds once and then pay in small steps as it uses a service, with those payments settled together later. Sessions suit work with many repeated calls, such as model inference or data queries. For now they only run on Tempo, because they rely on an escrow contract on that chain.

In practice the directory still leans heavily on stablecoins and one-off charges. The services using sessions are the high-volume ones, including Anthropic, Google Gemini, OpenRouter and Dune.

Who is using it

MPP launched on March 18, 2026, alongside the Tempo mainnet. Visa, Mastercard, Anthropic, OpenAI and Shopify were among the companies involved at launch. Early Stripe users included Browserbase, which charges agents per browser session, and PostalForm, which lets agents pay to print and mail letters. Prospect Butcher Co. in New York even took sandwich orders from agents. Parallel Web Systems uses MPP so agents can pay per API call for web search.

Usage has grown quickly since then, though from a small base. MPPScan, a public tracker run by Merit Systems, counts MPP payments that settle on Tempo. Card payments through Stripe are not in these numbers.

In late July, Stripe CEO Patrick Collison said MPP was nearing 30,000 transactions a day. The average payment is tiny, about 13 cents in one June count, which fits the pay-per-call pattern. Total dollar volume is still small, and Circle has pointed out that large institutions have not yet started sending real volume through agent payments.

The public directory now covers a wide spread of tools an agent might need. It includes web search from Exa and Parallel, web scraping from Firecrawl, market data from CoinGecko and Alpha Vantage, and image generation from fal.ai. Each one charges by the call, with no account or API key.

How it compares

MPP is one of several agent payment standards, and they do not all solve the same problem. Some move the money, others handle checkout or permission.

Protocol	Backed by	What it handles	Payment rails
MPP	Stripe and Tempo	Paying inside a web request, one-off or by session	Stablecoins, cards, buy now pay later, Lightning
x402	Coinbase, now the x402 Foundation at the Linux Foundation	Paying inside a web request	Mainly stablecoins such as USDC
ACP	OpenAI and Stripe	Agent checkout with merchants	Cards through Stripe
AP2	Google	Proof that a user approved an agent’s purchase	Works across rails

The closest match is x402, which also uses the 402 status code. It had a head start and reports far more activity, with over 140 million total transactions, though one analysis found about half of that was not real demand. MPP’s main differences are card support from day one and sessions for repeated calls. Stripe supports both protocols, and some services, such as APIbase, already accept both on the same endpoint.

What to watch

Three things will shape MPP over the next year. The first is standards: the core spec has been submitted to the IETF, the group that maintains web standards such as HTTP. The second is reach: sessions outside Tempo and support for more blockchains are still on the roadmap. The third is demand: most activity today comes from developer tools and data APIs rather than everyday purchases.

There are open questions too. Businesses need clear answers on who is responsible when an agent overspends or buys the wrong thing. Spending limits on Shared Payment Tokens help, but disputes, identity checks and audit trails for agent purchases are still being worked out across the industry.

For a business already on Stripe, trying MPP costs little. Agent payments land in the same balance and dashboard as other Stripe payments and follow the same payout schedule. They also use the same fraud checks, tax tools and refund process. If you sell an API, data or compute by the call, MPP is worth testing now.