Tutorials, comparisons and design patterns for building autonomous agents that self-fund, call 345+ models and orchestrate MCP Tools.
x402's fourth scheme adds the one thing exact never had: a way to get money back. We read both spec documents, the shipped TypeScript, and the escrow contract itself — then swept 24 hours of Base mainnet to see who is actually using it. The scheme is client-only, its fee semantics have already drifted from upstream, and the refund machinery it exists for fires on 0.28% of payments.
The x402 spec everyone reads is 4,252 words. The extension specs nobody reads are 14,820. We audited all nine — sign-in-with-x, offer-receipt, auth-hints, payment-identifier, builder-code, gas sponsoring, HTTP message signatures, Bazaar — mapped which SDKs actually implement them (TypeScript 7 of 9, Python and Go 4 of 9), traced a month of security patches, and found three verifiable inconsistencies between the specs and the shipped code.
We cloned tempoxyz/mpp-specs and read all 23 specification documents of the Machine Payments Protocol, the Stripe + Tempo rival to x402. MPP registers a real HTTP authentication scheme, ships payment channels as a first-class primitive, carries fiat rails through Shared Payment Tokens, and defines an MCP transport. We also found wire examples that contradict their own prose, a credential example missing a required field, and an MCP binding pinned to a superseded spec revision.
Our facilitator API deep dive ended with a one-line escape hatch: self-host with x402-rs. This is the follow-up. We cloned the repo at HEAD, read the config parser, probed the maintainer's live testnet instance, and found both the strongest open-source settlement plane in the ecosystem and three documentation bugs that will bite anyone deploying it.
The W3C WebMCP draft turns any web page into an in-browser MCP-style tool server via document.modelContext. We read the spec (28-Jul-2026 draft), the declarative form proposal, and Cloudflare's one-switch deployment — and map the two things the standard deliberately leaves out: agent identity and payments.
Between 2 and 7 August, Cloudflare ran its first Agents Week and published a stack that covers the four verbs it says the agentic web needs: readable, discoverable, callable, payable. Wallets and cloudflare.pay gave agents a buy side. The new MCP spec reached production infrastructure nine days after going final. Workers AI and AI Gateway merged into one control plane with cross-provider failover and a single credit balance. And OSL launched a payment rail that speaks x402, AP2 and MPP at once.
Nanopayments powered by Circle Gateway went live on mainnet on 29 April 2026: gas-free USDC payments down to $0.000001, on eleven chains, using the x402 protocol. The mechanism is not a new scheme — it is the standard exact scheme with a different EIP-712 domain, a Gateway Wallet contract as verifyingContract, and settlement deferred into a batch signed inside an AWS Nitro Enclave. We walk the whole path: deposit, 402, TransferWithAuthorization, off-chain debit, batch, withdrawal. Then the constraints the marketing does not lead with: authorizations must stay valid at least three days, deposits on Ethereum-anchored chains take 13 to 19 minutes, smart contract accounts are excluded because the batch path verifies with ecrecover, and Solana is supported by Gateway but not by Nanopayments.
The Agent Directory Service is the discovery layer of AGNTCY, the Linux Foundation project that Cisco contributed in July 2025. It stores agent records as OCI artifacts addressed by content identifier, indexes them in a Kademlia DHT keyed on a skill taxonomy, and signs them with Sigstore. We read the IETF draft end to end, audited the dir and oasf repositories, and crawled the public staging registry on 6 August 2026: 9,814 artifacts, an estimated 1,900 records, three quarters of them with no address to call and none with a price.