Tutorials, comparisons and design patterns for building autonomous agents that self-fund, call 345+ models and orchestrate MCP Tools.
L402 turned HTTP 402 into a working protocol five years before x402 existed: a macaroon that commits to a Lightning payment hash, verified statelessly against a preimage. We audited the spec, the standardization trail, and Aperture's source tree as of 2026-08-18. bLIP-26 has been an open pull request since June 2023 with 91 review comments and no merge. Neither L402 nor Payment appears in the IANA HTTP authentication scheme registry. And Aperture now emits three offers on one 402, because Lightning Labs shipped the Stripe/Tempo Payment scheme next to its own.
ERC-8004 deploys three registries: identity, reputation, validation. We audited the Solidity in erc-8004/erc-8004-contracts and measured what each registry actually holds on Ethereum and Base. Identity works. Reputation is thin. Validation has never been used on Ethereum. And a single EOA can upgrade all three.
On 19 July 2026 Skyfire published six Internet-Drafts defining KYAPay: a JWT family that carries who authorized an agent, how that human was verified, which AML screening ran, and how the request will be paid — all in one HTTP header. Co-authors come from Experian, Akamai, Okta and Ory. We read the raw drafts, audited the three IANA registries they target, and compared them against what Skyfire ships in production today. Registered claims: zero.
We cloned a2aproject/A2A on 2026-08-15 and read the specification, the proto and the SDK compatibility layers. A2A 1.0 unified Part types, renamed every enum, moved errors to google.rpc.Status and made version negotiation a header. It also added signed Agent Cards and a two-tier extension governance framework that, as of today, holds zero official extensions. The x402 payment extension still speaks the 0.3 wire format.
Between 6 and 13 August the supply side of the agent stack advanced on four fronts at once: a vendor-neutral packaging format for skills and MCP servers, EC2-backed agent sessions that live for two weeks, an open source model router with published cost curves, and a browser engine that reads the web for a fraction of Chromium's memory. In the same week, the only public demand-side number moved the other way: x402 daily settlement volume is down 93% year to date.
We cloned open-telemetry/semantic-conventions-genai on 2026-08-14 and read every model file. Sixty-three gen_ai attributes, five agent span types, MCP context propagation through params._meta — and zero attributes for money. PR #443, opened five days ago, would add gen_ai.usage.cost.* as a float. That is the exact place where telemetry stops and settlement begins.
Three purpose-built payment chains went live or were dated in 2026: Tempo (Stripe, mainnet March 18), Kite (April 30) and Arc (Circle, September 16). We cloned the x402 reference implementation and read each chain's docs. The binding constraint is not the chain — it is the token interface underneath it.
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.