x402

Definition and operation

x402 uses a minimal design separating server, client, facilitator and blockchain, which keeps chains and assets interchangeable. The payment flow has four components: the client (the party requesting a service), the server (the service provider that returns 402 and serves the paid resource), the facilitator (which executes and verifies payment), and the blockchain (the settlement layer where the stablecoin transfer occurs). At the protocol level the server returns a PAYMENT-REQUIRED header (payment conditions as JSON), the client sends a PAYMENT-SIGNATURE header (signed payment proof), and the server may return an optional PAYMENT-RESPONSE header confirming settlement.

The payment conditions a server advertises include the payment scheme (exact for fixed amounts, with experimental support for usage-based upto), a CAIP-2 network identifier (Base, for example, is eip155:8453), the asset contract address (usually USDC), the payee address, a maximum amount, an expiry time, and an optional facilitator endpoint URL. Clients sign payments without exposing private keys. A facilitator resembles a traditional payment service provider but differs in that it neither holds funds nor controls wallet private keys.

History

The HTTP 402 "Payment Required" status code sat reserved in early specifications and went effectively unused for roughly 30 years, while the web substituted advertising, paywalls and credit-card checkout forms. Its intellectual lineage runs from that 1990s reservation to 21.co's early-2010s experiments with HTTP-based bitcoin micropayments, which were hard to realise because of the expensive setup and teardown of bitcoin payment channels.

Coinbase published x402 with a whitepaper on 6 May 2025 (authored by Erik Reppel, Nemil Dalal, Dan Kim and others), and Galaxy Research also dates the launch to May 2025. Coinbase stated that falling L2 fees, as on Base, made previously impossible applications feasible. On 23 September 2025 Coinbase announced plans for an x402 foundation together with Cloudflare, and after six months of feedback on v1 it released x402 V2 on 11 December 2025. V2 expanded along three lines: a unified payment interface supporting multiple blockchains and assets (including legacy payment rails and facilitator integration), wallet-based identity with reusable access sessions, and automatic service discovery; it supports subscriptions, prepaid access, usage-based billing and multi-step agent workflows.

On 2 April 2026, at the MCP Dev Summit North America in New York, the Linux Foundation announced the launch of the x402 Foundation along with Coinbase's contribution of the x402 protocol; Adyen, AWS, American Express, Base, Circle, Cloudflare, Coinbase, Fiserv, Google, KakaoPay, Mastercard, Microsoft, Polygon Labs, PPRO, Shopify, Solana Foundation, Stripe, thirdweb and Visa were among those signalling participation. On 14 July 2026 the Linux Foundation announced that the foundation had begun operating and Coinbase had completed its contribution, with 40 organisations joining as members. The foundation manages the protocol under vendor-neutral, community governance, runs working groups and maintains reference implementations.

Examples

At launch AWS, Anthropic, Circle and NEAR were among the collaboration partners, with Circle's USDC central to early payments. Early examples included Hyperbolic (per-GPU-inference payment), OpenMind (robots procuring compute and data), Anthropic MCP (tools, context search and payment), NEAR AI, XMTP, Neynar (on-demand billing for the Farcaster API), Chainlink and Zyte.

The characteristic use case is an agent paying per API call. A trading agent can buy individual API calls from the blockchain data provider Nansen, and the decentralised AI lab Nous Research enabled x402 payment for access to its Hermes 4 model. In API and data monetisation the provider charges per request or per data unit and settles inside the same HTTP call, so users gain access without accounts, API keys or prepaid credit. In agent-to-agent payment a client agent pays a server agent through the same 402 flow for services, outputs or specialist capabilities: a research agent can settle a dataset purchase from a data agent, and a planning agent a model call from an inference agent, per transaction.

Monetising access to data and context is another representative use. Widely used AI systems such as ChatGPT cannot autonomously reach content behind paywalls, so users had to buy subscriptions and transfer information manually. Cloudflare introduced Pay-per-Crawl in 2024, letting bots and crawlers pay for access instead of being blocked, and later announced plans for x402 integration.

As of April 2026, production deployments included Coinbase Agent.market (a directory of x402-paid services), Stripe Machine Payments (previewed 10 February 2026, USDC on Base), CoinGecko paid endpoints (0.01 USDC per request, paid on Base or Solana), the Circle Wallets reference workflow and the Cloudflare Agents SDK. On EVM, EIP-3009 (transferWithAuthorization tokens such as USDC) is the simplest route with a single off-chain signature, while Permit2 serves as a universal fallback for any ERC-20 token and requires a one-time on-chain approval; both provide gasless transfers with the facilitator covering gas.

Relations

x402 occupies the execution and settlement layer of the agentic payment standards. The checkout and merchant-integration layer includes ACP (OpenAI and Stripe, open-sourced September 2025, first deployed in ChatGPT Instant Checkout); the authorisation and trust layer includes AP2 (Google, with more than 60 organisations, based on signed mandates); and the session and settlement layer includes MPP (Stripe and Tempo, released 18 March 2026). Several analyses judge these complementary rather than competing because they occupy different layers: an agent system can combine AP2 for spending authority, ACP for merchant commerce, and x402 or MPP for settlement.

MCP (Model Context Protocol) connects models to tools and context but is not a payment layer, so agents combine it with x402, reaching tools through MCP and paying for them through x402. Google worked with Coinbase and MetaMask on AP2 to release an A2A x402 extension, and Visa said it supports the x402 Foundation so that payments can occur wherever AI agents transact with cards or stablecoins, embedding x402 interoperability in its Trusted Agent Protocol after observing a 4,700% surge in AI-driven retail traffic in 2025. Financial infrastructure firms such as Fireblocks contributed security extensions for request integrity and spending governance to the x402 Foundation.

x402 is designed as a chain-agnostic protocol: CAIP-2 identifiers can express any EVM chain, including Ethereum and Base, as well as Solana, and the specification enumerates token support for many networks including TON, Algorand, Stellar, Aptos, Hedera, Keeta, NEAR, Concordium, XRPL and Cardano. The Coinbase facilitator (CDP Facilitator) supports EVM networks such as Base, Polygon, Arbitrum and World plus Solana, and Stellar joined the EVM and SVM tracks in March 2026 with a production facilitator built on the OpenZeppelin Relayer. Base's two-second blocks and sub-0.1-cent gas, and Solana's roughly 0.5-second finality at similar fees, give sub-dollar payments the best economics.

Distinctions

x402 is an execution and settlement layer protocol settling stablecoins inside the HTTP request-response cycle, whereas ACP is a checkout and merchant-integration layer for how agents interact with merchants (today largely fiat), AP2 is an authorisation and trust layer that moves no funds (covering cards, bank transfers and stablecoins alike), and MPP is a session-based approval and streaming payment layer (stablecoins, cards, Lightning). x402 is optimised for small machine-to-machine payments for APIs, data and compute and does not address physical goods commerce or human-facing checkout. ACP, by contrast, is oriented to human-involved fiat purchases and does not by default provide machine-to-machine micropayments or stablecoin settlement.

Both x402 and MPP use HTTP 402, but MPP is a session and settlement layer that streams micropayments under pre-authorised sessions, unlike x402's per-request settlement model, and some assessments consider it less permissionless because of its Stripe and Tempo dependence. x402 is an open standard supporting multiple chains and assets rather than one blockchain or token, yet although the specification allows non-blockchain network expansion, in practice it remains centred on stablecoins, especially USDC. The design is stateless, so session handling falls outside the specification, and at very high micropayment frequency per-request on-chain settlement can become costly; V2's batch-settlement, upto and auth-capture schemes offset this limit.

Early adoption relied heavily on Coinbase's hosted facilitator, and that concentration of facilitator trust is noted as a potential security and centralisation risk. Reported cumulative usage conflicts across aggregators and dates: about 165 million transactions and roughly $46.5 million on x402scan as of 18 March 2026, about 69,000 active agents with 165 million transactions and roughly $50 million in Coinbase reporting at the end of April 2026, and more than 140 million transactions and over $600 million in August 2026 material. No single figure should be asserted as definitive; figures should be given with their source and date.

Fee structures also differ by layer. The x402 protocol itself charges no processing fee, and users pay only the settlement chain's blockchain fee (under one cent on Base and Solana, around $0.0001 per request). Coinbase's hosted facilitator (CDP), however, is free for up to 1,000 transactions a month and charges $0.001 per transaction thereafter. Card-based ACP and AP2 routes carry Stripe processing fees (typically 2.9% plus $0.30 on cards), which is unfavourable for small transactions.

Limits and criticism

Speculative activity drove x402's early adoption. In late October 2025 teams issued and traded memecoins such as PING on x402 and volumes surged; as memecoin activity faded, volumes and transaction counts fell sharply, with weekly volume dropping about 96% from a $5.3 million peak in November 2025 to under $220,000 in February 2026. Visa stated that roughly 95% of 2025 x402 transaction value was memecoin-related. Since then agent-to-agent services, data services and infrastructure or utility usage have grown, and the share of gaming transactions classified as self-trading or wash trading fell below 50% after early December 2025. Despite the volume collapse, protocol-level activity held up and is recovering: by March 2026 Base had processed more than 119 million transactions worth about $35 million and Solana 35 million worth about $10 million, making Solana a major second settlement layer.

Some assessments hold that many real-world examples are concept proofs demonstrating infrastructure capability rather than substantial growth drivers. Because payment is an on-chain token transfer, every attempt is auditable: when something goes wrong, an agent's wallet address and chain can be traced to check whether the signed authorisation reached actual settlement. As of August 2026 the x402 specification published exact scheme bindings for 16 chains, admits CAIP-2 identifiers for non-blockchain networks (for example ach:us, sepa:eu) and already provides a cloudflare:402 binding.