# Roundhouse resources Explainers, comparisons and guides on agent payments: the x402 protocol, ERC-8004 identity, and what the settlement record actually shows. Published by Roundhouse AI Ltd. Every article is served twice: as HTML at the path shown, and as markdown at the same path plus `.md`. Each one opens with a self-contained answer to the question in its title. ## Adding x402 to an API you already run Adding x402 to an existing API means returning 402 with payment terms on priced routes, verifying the payment with a facilitator before doing work, binding it to the specific resource, tracking nonces before serving, and settling. The code is typically a day. The decisions about resource binding and serve order are the part to get right first. - URL: https://roundhouseai.io/resources/add-x402-to-an-existing-api - Markdown: https://roundhouseai.io/resources/add-x402-to-an-existing-api.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Agent cards and A2A discovery, and where they stop An agent card is a JSON document at a well-known path describing an agent's identity, endpoints, skills and authentication. Another agent reads it before delegating work. A2A reached v1.0.0 in March 2026. The limitation is that the card answers what this agent does, never which agent can do a given thing. - URL: https://roundhouseai.io/resources/agent-cards-and-a2a-discovery - Markdown: https://roundhouseai.io/resources/agent-cards-and-a2a-discovery.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Agent payment protocols compared, October 2026 Four standards matter in late 2026. x402 settles per-request micropayments on-chain, MPP does similar work through Stripe's rails, ACP structures agent checkout with merchants on card rails, and AP2 proves a user authorised a purchase without moving money. Price point and buyer type decide between them, and none provides spending limits. - URL: https://roundhouseai.io/resources/agent-payment-protocols-compared-2026 - Markdown: https://roundhouseai.io/resources/agent-payment-protocols-compared-2026.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Spending controls for an agent's wallet An agent's spending limits are enforced either by a provider's policy engine, which is flexible and depends on that infrastructure, or by on-chain permission grants, which are rigid and depend on nothing. The controls worth having are a per-transaction cap, a rolling budget, a counterparty allowlist, a short expiry and a kill switch. - URL: https://roundhouseai.io/resources/agent-wallet-spending-controls - Markdown: https://roundhouseai.io/resources/agent-wallet-spending-controls.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Can an AI assistant pay for something on its own? Most mainstream AI assistants cannot spend money directly. Payment requires a funded wallet and the ability to sign, which assistants do not have by default. Where an agent does pay, it is through a wallet its operator created and funded, under spending limits the operator configured, usually using x402 for per-call purchases. - URL: https://roundhouseai.io/resources/can-ai-assistants-pay-for-things - Markdown: https://roundhouseai.io/resources/can-ai-assistants-pay-for-things.md - Published: 2026-10-14 · reviewed 2026-10-14 ## EIP-3009 explained, and why x402 is built on it EIP-3009 is a token standard that adds TransferWithAuthorization, letting a holder sign a transfer off-chain that anyone else can then submit. x402 uses it so a buyer can pay with a signature alone, holding no native token for gas. USDC implements it, which is most of why x402 settles in USDC. - URL: https://roundhouseai.io/resources/eip-3009-transfer-with-authorization-explained - Markdown: https://roundhouseai.io/resources/eip-3009-transfer-with-authorization-explained.md - Published: 2026-10-14 · reviewed 2026-10-14 ## ERC-8004 explained, and what the research found ERC-8004 is a draft Ethereum standard giving agents on-chain identity, reputation and validation registries. Registries launched in January 2026 and adoption figures run into the hundreds of thousands of agents across many networks. An empirical study found most registrations were placeholders and concluded the reputation layer cannot currently function as a trust signal. - URL: https://roundhouseai.io/resources/erc-8004-explained - Markdown: https://roundhouseai.io/resources/erc-8004-explained.md - Published: 2026-10-14 · reviewed 2026-10-14 ## How an agent chooses between two services that do the same thing An agent comparing equivalent services filters on what it can actually pay for, then ranks on price and latency, then on whatever evidence of reliability is available. Brand and familiarity carry no weight. A seller wins by being legible in the comparison, which means a fixed price, a readable interface and a public history. - URL: https://roundhouseai.io/resources/how-agents-choose-between-services - Markdown: https://roundhouseai.io/resources/how-agents-choose-between-services.md - Published: 2026-10-14 · reviewed 2026-10-14 ## How AI agents discover and pay for services An agent finds a paid service four ways: a facilitator's catalogue, the publisher's own well-known documents, the on-chain settlement record, or an index that joins all three. Catalogues alone are incomplete: over three days in September 2026, 1,950 wallets were paid through named facilitators and only 641 appeared in any catalogue. - URL: https://roundhouseai.io/resources/how-agents-discover-paid-services - Markdown: https://roundhouseai.io/resources/how-agents-discover-paid-services.md - Published: 2026-10-14 · reviewed 2026-10-14 ## How AI agents pay for APIs: x402, API keys and cards compared An agent can pay for an API three ways: a pre-issued API key billed to a human's card, a prepaid credit balance it draws down, or an x402 payment attached to the request itself. Only the third works when the agent and the seller have never met, because the first two require a sign-up a machine cannot complete. - URL: https://roundhouseai.io/resources/how-ai-agents-pay-for-apis - Markdown: https://roundhouseai.io/resources/how-ai-agents-pay-for-apis.md - Published: 2026-10-14 · reviewed 2026-10-14 ## How much x402 volume is real? Independent analyses through 2026 consistently found that most reported x402 volume is not genuine commerce. Artemis estimated roughly half of transactions were self-dealing or wash trading. An a16z and Allium analysis cut a $3M figure to about $1.6M. TRM Labs estimated 0.6% to 7.5% of screened activity was plausibly agentic. - URL: https://roundhouseai.io/resources/how-much-x402-volume-is-real - Markdown: https://roundhouseai.io/resources/how-much-x402-volume-is-real.md - Published: 2026-10-14 · reviewed 2026-10-14 ## How to audit an x402 service's claimed traffic Audit an x402 service by reading the settlement record for its receiving address rather than its own numbers. Check distinct buyers over time, the share of volume from the largest payer, self-payments, the age of the first settlement, the amount distribution, the relayer mix, and whether the address appears in any catalogue. - URL: https://roundhouseai.io/resources/how-to-audit-an-x402-services-traffic - Markdown: https://roundhouseai.io/resources/how-to-audit-an-x402-services-traffic.md - Published: 2026-10-14 · reviewed 2026-10-14 ## How to price an endpoint when the buyer is an agent Price an endpoint for agents by starting from your cost per call, checking what comparable endpoints charge, and pricing so the number is directly comparable. Agents compare on price and latency with no switching cost, so legibility matters as much as the level, and a ceiling-based price loses to a fixed one in automated comparison. - URL: https://roundhouseai.io/resources/how-to-price-an-endpoint-for-agents - Markdown: https://roundhouseai.io/resources/how-to-price-an-endpoint-for-agents.md - Published: 2026-10-14 · reviewed 2026-10-14 ## HTTP 402 Payment Required, and why it took 30 years to use HTTP 402 Payment Required is a status code reserved in the 1997 HTTP/1.1 specification and deliberately left undefined. It went unused because there was no way for a browser to pay a stranger automatically. Stablecoins and signature-based transfers supplied one, and x402 is the first widely deployed definition of what a 402 response should contain. - URL: https://roundhouseai.io/resources/http-402-payment-required-explained - Markdown: https://roundhouseai.io/resources/http-402-payment-required-explained.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Know Your Agent, and what it can honestly establish Know Your Agent is the practice of establishing who or what is behind an agent before transacting with it. Unlike KYC it cannot verify a legal identity, because an agent presents a wallet key rather than a person. What it can establish is a signed claim bound to a key, plus the public behaviour of that key. - URL: https://roundhouseai.io/resources/know-your-agent-kya-explained - Markdown: https://roundhouseai.io/resources/know-your-agent-kya-explained.md - Published: 2026-10-14 · reviewed 2026-10-14 ## llms.txt explained, and what it is actually good for llms.txt is a convention for publishing a plain markdown index at your site root describing what the site offers and where. It helps a model that has already reached your domain understand it without parsing HTML. It does not help anything find you, and it is a convention rather than a ratified standard. - URL: https://roundhouseai.io/resources/llms-txt-explained - Markdown: https://roundhouseai.io/resources/llms-txt-explained.md - Published: 2026-10-14 · reviewed 2026-10-14 ## How to make your API discoverable to AI agents An agent finds a paid API through a facilitator catalogue, by probing the host directly, through the settlement record of payments you have received, or through an index that joins all three. Being findable means registering with catalogues, publishing machine-readable files at well-known paths, and accepting payments that leave a public trace. - URL: https://roundhouseai.io/resources/make-your-api-discoverable-to-ai-agents - Markdown: https://roundhouseai.io/resources/make-your-api-discoverable-to-ai-agents.md - Published: 2026-10-14 · reviewed 2026-10-14 ## MCP, A2A and x402: which layer does what MCP connects a model to tools and data. A2A lets agents find and delegate to each other. x402 moves money for a request. They are a tool layer, a coordination layer and a payment layer, and a working agent system usually runs all three without any of them overlapping. - URL: https://roundhouseai.io/resources/mcp-a2a-x402-which-layer-does-what - Markdown: https://roundhouseai.io/resources/mcp-a2a-x402-which-layer-does-what.md - Published: 2026-10-14 · reviewed 2026-10-14 ## How to charge for an MCP server with x402 MCP has no payment primitive, so a paid MCP server charges at the HTTP transport underneath rather than per tool call. A tool call cannot carry an X-PAYMENT header, so the common pattern is a prepaid balance on the account behind the connection, drawn down per call, with x402 used to top that balance up. - URL: https://roundhouseai.io/resources/monetise-an-mcp-server-with-x402 - Markdown: https://roundhouseai.io/resources/monetise-an-mcp-server-with-x402.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Prompt injection when the agent can spend money Prompt injection is the insertion of instructions into content an agent reads, causing it to act on the attacker's goals. When the agent can pay, the consequence is a payment the user never intended, carried out with the user's own valid credentials. Signed authorisation proves consent was given, not that it was informed. - URL: https://roundhouseai.io/resources/prompt-injection-and-agent-payments - Markdown: https://roundhouseai.io/resources/prompt-injection-and-agent-payments.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Publishing an x402 service: the checklist Publishing an x402 service means returning a correct 402 with full terms, verifying and settling through a facilitator, binding the payment to the resource, keeping a free discovery path, registering with catalogues, and publishing machine-readable declarations. The order matters because each step unblocks the next. - URL: https://roundhouseai.io/resources/publish-an-x402-service-checklist - Markdown: https://roundhouseai.io/resources/publish-an-x402-service-checklist.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Rate limiting when your buyer is an agent With x402 every request is paid before it is served, so volumetric abuse is self-limiting: an attacker's worst case is buying a lot of your product at your price. The limits still worth having are on unpaid 402 traffic, on concurrency per payer, and on the facilitator calls your own server makes. - URL: https://roundhouseai.io/resources/rate-limiting-when-your-buyer-is-an-agent - Markdown: https://roundhouseai.io/resources/rate-limiting-when-your-buyer-is-an-agent.md - Published: 2026-10-14 · reviewed 2026-10-14 ## How to read an agentic payments dashboard without being misled Agentic payment dashboards usually show accurate figures over populations they do not define. Before reading one, establish which chains it covers, what window, what evidence standard decided what counts, whether self-dealing was removed, and how stale the data is. Without those, a chart is not comparable with any other chart. - URL: https://roundhouseai.io/resources/reading-an-agentic-payments-dashboard - Markdown: https://roundhouseai.io/resources/reading-an-agentic-payments-dashboard.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Refunds and failures in x402, and how to handle both An x402 settlement is final and has no reversal mechanism, so a refund is a new payment the seller chooses to send. The cases to design for are payment verified but not settled, settled but the work failed, and settled twice. Each has a correct handling and none of them is a dispute process. - URL: https://roundhouseai.io/resources/refunds-and-failures-in-x402 - Markdown: https://roundhouseai.io/resources/refunds-and-failures-in-x402.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Should you run your own x402 facilitator? Running your own facilitator means operating the verify and settle path yourself: an RPC endpoint, a funded hot wallet, nonce management, gas monitoring and reorg handling. It is worth it if you already run on-chain infrastructure, if fees are material at your volume, or if a third party in your payment path is unacceptable. - URL: https://roundhouseai.io/resources/run-your-own-x402-facilitator - Markdown: https://roundhouseai.io/resources/run-your-own-x402-facilitator.md - Published: 2026-10-14 · reviewed 2026-10-14 ## How to screen a counterparty before paying it Screen a payee by reading its public settlement history: distinct counterparties, largest payer share, self-payment rate, age of first settlement, amount distribution and relayer attribution. When the record is empty or thin, cap the first payment instead, because an absent history is not a clean one. - URL: https://roundhouseai.io/resources/screen-an-agent-counterparty-before-paying - Markdown: https://roundhouseai.io/resources/screen-an-agent-counterparty-before-paying.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Which stablecoin should an agent pay with? USDC carries the overwhelming majority of x402 payments because it implements EIP-3009, the mechanism that lets a buyer pay with a signature and no gas token. Assets without an equivalent authorisation path need extra steps or cannot be used at all, so asset choice is constrained by the protocol rather than by preference. - URL: https://roundhouseai.io/resources/stablecoins-for-agent-payments-compared - Markdown: https://roundhouseai.io/resources/stablecoins-for-agent-payments-compared.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Testing x402 on a testnet, and what will still break on mainnet Test x402 on Base Sepolia or another supported testnet using a testnet-only facilitator, which the default at x402.org is. The happy path transfers cleanly. What testnets do not reproduce is the EIP-712 domain difference between testnet and mainnet token contracts, realistic settlement latency, and facilitator failure behaviour under load. - URL: https://roundhouseai.io/resources/test-x402-on-a-testnet - Markdown: https://roundhouseai.io/resources/test-x402-on-a-testnet.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Wash trading in agentic commerce, and how to spot it Wash trading in agent payments means manufacturing settlements between wallets you control to inflate volume and transaction counts. It is cheap because gas on the chains x402 uses costs fractions of a cent. The patterns that expose it are self-payment, buyer concentration, circular flows, uniform timing and uniform amounts. - URL: https://roundhouseai.io/resources/wash-trading-in-agentic-commerce - Markdown: https://roundhouseai.io/resources/wash-trading-in-agentic-commerce.md - Published: 2026-10-14 · reviewed 2026-10-14 ## The well-known files an agent looks for on your domain Agents probe a handful of paths under /.well-known to learn what a domain offers: an agent card for A2A, an x402 declaration for priced endpoints, OAuth metadata for authentication, and an OpenAPI document. The trap is that many hosts answer 404 with a JSON content type, so a crawler checking the type rather than the status reads absence as presence. - URL: https://roundhouseai.io/resources/well-known-files-agents-look-for - Markdown: https://roundhouseai.io/resources/well-known-files-agents-look-for.md - Published: 2026-10-14 · reviewed 2026-10-14 ## What is a settlement, and why is it the unit that matters? A settlement is a payment that has been included in a block and moved funds. It is distinct from an authorisation, which is a signed promise, and from a request, which may never have been paid for at all. Only settlements are facts about the world, which is why a record of agent commerce should be built from them. - URL: https://roundhouseai.io/resources/what-is-a-settlement-in-agent-payments - Markdown: https://roundhouseai.io/resources/what-is-a-settlement-in-agent-payments.md - Published: 2026-10-14 · reviewed 2026-10-14 ## What is an x402 facilitator, and do you need one? A facilitator is the service that checks an x402 payment authorisation is valid and then settles it on-chain. It exposes two endpoints, verify and settle, and it pays the gas. Because it submits the transaction, the on-chain sender is the facilitator rather than the payer, which is what makes x402 payments identifiable afterwards. - URL: https://roundhouseai.io/resources/what-is-an-x402-facilitator - Markdown: https://roundhouseai.io/resources/what-is-an-x402-facilitator.md - Published: 2026-10-14 · reviewed 2026-10-14 ## What is x402? The HTTP payment protocol AI agents use x402 is an open protocol that lets a client pay for an HTTP request at the moment it makes it. The server answers 402 Payment Required with machine-readable terms, the client signs a stablecoin authorisation, and it resends the request with an X-PAYMENT header. No account, no API key, no human. - URL: https://roundhouseai.io/resources/what-is-x402 - Markdown: https://roundhouseai.io/resources/what-is-x402.md - Published: 2026-10-14 · reviewed 2026-10-14 ## What proves a transfer was an x402 payment? The gasless-transfer marker that x402 produces is not proof of x402, because the same mechanism predates the protocol and is used by unrelated systems. The discriminator is the transaction sender: on the common path it is a facilitator. A transfer relayed by a named facilitator is strong evidence; one relayed by an unknown address is unestablished rather than disproven. - URL: https://roundhouseai.io/resources/what-proves-a-transfer-was-an-x402-payment - Markdown: https://roundhouseai.io/resources/what-proves-a-transfer-was-an-x402-payment.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Which blockchains support x402? x402 can address any chain by identifier, so spec support is broad. Live settlement is narrower. Through 2026 the chains carrying real x402 volume were Base and Solana, with Stellar, Polygon and Avalanche reachable through facilitators. A chain is usable when a facilitator and a client both support it, not when the spec permits it. - URL: https://roundhouseai.io/resources/which-blockchains-support-x402 - Markdown: https://roundhouseai.io/resources/which-blockchains-support-x402.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Who pays the gas in an x402 payment? The facilitator pays the gas. An x402 buyer signs an authorisation rather than sending a transaction, so it needs no native token at all. The facilitator wraps the signature in a transaction, pays for the block space and recovers that cost through its own pricing. On a cheap chain the gas is a fraction of a cent. - URL: https://roundhouseai.io/resources/who-pays-gas-in-x402 - Markdown: https://roundhouseai.io/resources/who-pays-gas-in-x402.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Why USDC carries almost all x402 payments USDC carries most x402 payments because it implements EIP-3009, the function that lets a holder authorise a transfer with a signature instead of a transaction. Without that, a buyer needs the chain's native token and must broadcast itself, which defeats the design. The protocol is asset-agnostic; the set of assets that work this way is small. - URL: https://roundhouseai.io/resources/why-usdc-dominates-x402 - Markdown: https://roundhouseai.io/resources/why-usdc-dominates-x402.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Why x402 transaction counts disagree by orders of magnitude Published x402 figures in 2026 ranged across several orders of magnitude because trackers counted different things. The main differences are evidence standard, chain coverage, whether self-dealing was removed, transactions against dollars, batched payments, and the measurement window. None of them is dishonest and all of them change the answer. - URL: https://roundhouseai.io/resources/why-x402-transaction-counts-disagree - Markdown: https://roundhouseai.io/resources/why-x402-transaction-counts-disagree.md - Published: 2026-10-14 · reviewed 2026-10-14 ## The X-PAYMENT header, and what the server sends back X-PAYMENT is the request header a client uses to attach a signed payment authorisation when it retries a request that returned 402. It carries base64-encoded JSON naming the scheme, the network and the signed payload. The server answers with X-PAYMENT-RESPONSE, which carries the settlement result including the transaction hash. - URL: https://roundhouseai.io/resources/x-payment-header-explained - Markdown: https://roundhouseai.io/resources/x-payment-header-explained.md - Published: 2026-10-14 · reviewed 2026-10-14 ## x402 exact vs upto, and when to use each The exact scheme charges a price the server states before doing the work, and the client signs for that amount. The upto scheme authorises a maximum and settles for the actual cost once the work is done, which suits metered output. Exact is simpler and safer for buyers; upto is necessary when cost is unknowable in advance. - URL: https://roundhouseai.io/resources/x402-exact-vs-upto-schemes - Markdown: https://roundhouseai.io/resources/x402-exact-vs-upto-schemes.md - Published: 2026-10-14 · reviewed 2026-10-14 ## x402 facilitators compared, and how to pick one Coinbase CDP is the most used x402 facilitator and the default in most tutorials. thirdweb, PayAI and Cloudflare run alternatives, and the reference implementation can be self-hosted. The choice turns on chain coverage, pricing, documented replay handling and whether you can tolerate the facilitator being a single point of failure. - URL: https://roundhouseai.io/resources/x402-facilitators-compared - Markdown: https://roundhouseai.io/resources/x402-facilitators-compared.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Who governs x402, and what that means for building on it x402 is governed by the x402 Foundation, hosted by the Linux Foundation since April 2026, after Coinbase contributed the protocol. It launched with more than twenty founding members including Google, Visa, Stripe, AWS, Mastercard and Shopify. The specification and reference implementations are open source and developed in public. - URL: https://roundhouseai.io/resources/x402-foundation-governance - Markdown: https://roundhouseai.io/resources/x402-foundation-governance.md - Published: 2026-10-14 · reviewed 2026-10-14 ## x402 on Base, and what the record actually shows Base is where x402 launched in May 2025 and it held the cumulative volume lead through 2026. It has the longest-established tooling and the deepest settlement history, which also makes it the chain where the gap between gross transfer counts and verified x402 commerce is best documented. - URL: https://roundhouseai.io/resources/x402-on-base - Markdown: https://roundhouseai.io/resources/x402-on-base.md - Published: 2026-10-14 · reviewed 2026-10-14 ## x402 on Solana, and why the share figures disagree Solana carried a large share of x402 transaction activity through 2026, reported at roughly 70% of monthly activity by mid-August by several sources, while Base retained the cumulative lead. Solana payments use an SPL token flow rather than EIP-3009, which means an index covering both chains runs two different detectors. - URL: https://roundhouseai.io/resources/x402-on-solana - Markdown: https://roundhouseai.io/resources/x402-on-solana.md - Published: 2026-10-14 · reviewed 2026-10-14 ## The x402 accepts array, field by field The accepts array is the list of payment terms a server will take, sent in the body of its 402 response. Each entry names a scheme, a network, an asset contract, an amount in the asset's smallest unit, a payTo address and a timeout. A client picks one entry and signs an authorisation that matches it exactly. - URL: https://roundhouseai.io/resources/x402-payment-requirements-accepts-schema - Markdown: https://roundhouseai.io/resources/x402-payment-requirements-accepts-schema.md - Published: 2026-10-14 · reviewed 2026-10-14 ## The known attacks on x402, and what fixes each one Published research in 2026 identified settlement preemption, replay before settlement, resource substitution, free delivery from non-atomic verification, and a signature-validation flaw in a high-volume facilitator. The fixes are binding the payment to a resource, tracking nonces before serving, and checking that the caller is the authorised facilitator. - URL: https://roundhouseai.io/resources/x402-security-known-attacks - Markdown: https://roundhouseai.io/resources/x402-security-known-attacks.md - Published: 2026-10-14 · reviewed 2026-10-14 ## x402 v1 vs v2, and what to change in your integration Version 2 of x402 generalised the network and asset model so non-EVM chains, Solana in particular, became first-class rather than an extension. The HTTP exchange is unchanged. What breaks in older integrations is code that assumed a network name maps to an EVM chain id and that an asset is an ERC-20 address. - URL: https://roundhouseai.io/resources/x402-v1-vs-v2-what-changed - Markdown: https://roundhouseai.io/resources/x402-v1-vs-v2-what-changed.md - Published: 2026-10-14 · reviewed 2026-10-14 ## x402 vs ACP, and which one your checkout needs ACP is the Agentic Commerce Protocol from OpenAI and Stripe, which lets an agent complete a checkout with a merchant using a shared payment token on the merchant's existing processor. x402 prices individual HTTP requests and settles them in stablecoins on-chain. ACP is for buying goods; x402 is for buying compute, data and API calls. - URL: https://roundhouseai.io/resources/x402-vs-agentic-commerce-protocol-acp - Markdown: https://roundhouseai.io/resources/x402-vs-agentic-commerce-protocol-acp.md - Published: 2026-10-14 · reviewed 2026-10-14 ## x402 vs AP2, and why you probably need both AP2 is Google's Agent Payments Protocol, which produces signed mandates proving a user authorised an agent to buy something. It moves no money itself. x402 is a settlement protocol that moves money per HTTP request but carries no proof of human intent. A system that needs both authority and settlement uses both. - URL: https://roundhouseai.io/resources/x402-vs-ap2 - Markdown: https://roundhouseai.io/resources/x402-vs-ap2.md - Published: 2026-10-14 · reviewed 2026-10-14 ## x402 vs API keys: which should your API offer? API keys suit buyers who integrate deliberately and call you for months, because the sign-up cost is paid once and amortised. x402 suits buyers who discovered you seconds ago and want one call, because there is no sign-up at all. The two serve different buyers and most APIs benefit from offering both. - URL: https://roundhouseai.io/resources/x402-vs-api-keys-and-metered-billing - Markdown: https://roundhouseai.io/resources/x402-vs-api-keys-and-metered-billing.md - Published: 2026-10-14 · reviewed 2026-10-14 ## x402 vs L402, and what Lightning got right first L402 is a Lightning Network scheme that uses HTTP 402 with macaroon credentials and Lightning invoices. x402 uses 402 with stablecoin authorisations settled on public chains. L402 is cheaper and faster per payment but requires channel liquidity and a Bitcoin-denominated price, which is why stablecoin schemes took the agent market. - URL: https://roundhouseai.io/resources/x402-vs-l402-lightning - Markdown: https://roundhouseai.io/resources/x402-vs-l402-lightning.md - Published: 2026-10-14 · reviewed 2026-10-14 ## x402 vs Stripe's Machine Payments Protocol The Machine Payments Protocol is Stripe and Tempo's agent payment standard, launched in March 2026 alongside Tempo's mainnet. Like x402 it answers a request with payment requirements and takes a signed authorisation. It settles through Stripe PaymentIntents with Tempo as the default chain, and is rail-agnostic by design. - URL: https://roundhouseai.io/resources/x402-vs-stripe-machine-payments-protocol - Markdown: https://roundhouseai.io/resources/x402-vs-stripe-machine-payments-protocol.md - Published: 2026-10-14 · reviewed 2026-10-14 ## Per-call pricing vs subscriptions for AI products A subscription charges for access over time and smooths variable usage into a predictable bill. Per-call pricing charges for each unit of work and makes cost track usage exactly. Subscriptions suit products with ongoing human users; per-call pricing suits products bought by software that cannot commit to a month. - URL: https://roundhouseai.io/resources/x402-vs-subscriptions-for-ai-products - Markdown: https://roundhouseai.io/resources/x402-vs-subscriptions-for-ai-products.md - Published: 2026-10-14 · reviewed 2026-10-14 --- Articles: 53. Documentation: https://roundhouseai.io/docs.md