x402: The Settlement Layer for Autonomous Agents

Part 3 of our three-part series on the agentic commerce stack, written for directors who need to know how automated systems will pay each other and what that does to cost and control. Part 1 covered ACP, the checkout layer. Part 2 covered AP2, the authorisation layer.

In one paragraph

Once an agent has found what to buy (ACP) and proved it is allowed to (AP2), the money still has to move. The x402 protocol, built by Coinbase with Cloudflare on the long-unused HTTP 402 "Payment Required" status code, lets a client, including an AI agent, pay for a web resource inside a single request and receive it about two seconds later, with settlement in USDC stablecoin and transaction costs a fraction of a penny. For most UK businesses it is not something to adopt this year. It is something to understand, because it changes the economics of selling and buying anything priced per request.

The problem it solves

Traditional payment infrastructure assumes a human and a relationship: identity checks, billing addresses, account creation, API keys, minimum transaction sizes of 25 to 50 pence, and settlement in days. An AI agent carrying out a research task may need to use dozens of paid resources in seconds, each costing a fraction of a penny, from providers it has never dealt with. None of the existing rails can do that.

Gartner predicts that by 2028 90% of B2B transactions will be intermediated by AI agents. The question is not whether machines will transact autonomously, but which protocols will mediate it.

How it works, for a non-engineer

x402 has three participants:

• The client (a person's software or an AI agent) requests a resource. If payment is required it receives a 402 response stating the price, the wallet to pay and the network. It signs an authorisation for exactly that amount and resends the request with the signature attached. It never submits a blockchain transaction itself and never needs to hold a "gas" token to pay fees.
• The resource server (an API, a dataset, compute, content) states its price and hands the signed authorisation to a facilitator for verification and settlement, then delivers the resource once payment is confirmed. Coinbase describes the integration as "1 line for the server, 1 function for the client."
• The facilitator verifies the signature, submits the transfer on-chain, pays the network fee and returns a receipt. Coinbase's hosted facilitator processes USDC payments on Base and Solana without fees.

The whole cycle, request, challenge, authorisation, verification, settlement and delivery, takes about two seconds, per Avalanche's technical documentation. Every authorisation carries a unique nonce so it cannot be replayed.

The mechanism underneath is EIP-3009, a standard Circle proposed in 2020 for USDC that lets a signed message authorise a complete transfer which a third party can submit. That is what makes it free of gas fees for the payer. It is also the protocol's main constraint: only USDC natively supports it, and some bridged versions of USDC are incompatible.

What it costs, compared with the alternatives

For a system making a million API calls a month at one cent each, traditional processing would cost over $3,000 in fees and in practice is impossible because of minimums; x402 on Solana costs around $250 in network fees. That is a 10–100x difference, and it is what makes per-request pricing viable for the first time.

Adoption so far

x402 processed nearly 500,000 transactions between 14 and 20 October 2025, a 10,780% increase on four weeks earlier, and the x402.org dashboard reports over 75 million transactions in a trailing 30-day period. The x402 Foundation, announced by Coinbase and Cloudflare in September 2025, has over 40 partners including Cloudflare, AWS, Google Cloud, Anthropic (through MCP), Visa (through its Trusted Agent Protocol) and Circle.

x402 V2 adds wallet-based sessions for repeat access, automatic endpoint discovery, lifecycle hooks and multi-facilitator routing. Payment schemes beyond a fixed amount, such as "up to" a maximum based on consumption, are in the architecture.

The limitations, stated plainly

• Token support: USDC only, through EIP-3009, which ties the protocol to Circle's stablecoin.
• Facilitator dependence: the protocol limits what a facilitator can do, but most deployments rely on a small number of centralised facilitators, so their availability is your availability.
• Front-running: for contract-to-contract use, Circle recommends the variant that checks the caller is the intended payee.
• Regulation and accounting: stablecoin settlement is treated differently across jurisdictions, and finance teams need a policy for wallets, reconciliation and tax before anything goes live.

What this means for your business

• If you sell data, APIs or compute: per-request pricing becomes possible without subscriptions, invoicing or key management. That is a new product line for some businesses.
• If you run AI agents: every payment is tied to a specific request, so spend can be attributed to a task, an agent or a team with a precision subscriptions cannot give. Spending authority is bounded by the wallet balance, which is a natural rate limit.
• For finance and procurement: agents can access a new capability instantly and pay per use, without a procurement cycle. That is a control question before it is a convenience.
• For most UK SMEs: this is a two-to-three-year watch item rather than a 2026 project. The pattern to understand now is pay-per-request; the rail can be chosen later.

Where the stack ends up

ACP lets an agent complete a purchase with a merchant. AP2 proves the agent was authorised. x402 moves the funds when a stablecoin is the rail, and Google's A2A x402 extension connects the two so a mandate can be settled in one exchange. Together they are the infrastructure for a market that Bain estimates at $1.7 trillion by 2030. The HTTP 402 status code waited three decades for its purpose.

What to do now

1. Identify anything you sell or consume that is priced, or could be priced, per request.
2. Ask finance what a stablecoin wallet would mean for reconciliation, tax and policy, before any engineer experiments.
3. Decide the spending controls for agents first: budgets, approvals and logging are the same whichever rail settles the payment.

How Hexploits helps

We build agentic workflows with budgets, approvals and an immutable log, and the platforms they run on. For businesses selling per-request services we design the metering and integration that any settlement rail plugs into.

Request a proposal or talk to an engineer. You will have a written scope and an indicative price within two working days.

This concludes the series. Read Part 1: ACP and Part 2: AP2 for the full picture.