Tutorials, comparisons and design patterns for building autonomous agents that self-fund, call 345+ models and orchestrate MCP Tools.
AAuth gives every agent a signing key instead of an API key. Its Budgets extension adds a spending cap that the person's server sizes, the resource enforces, and that moves no money: payment stays on 402 and x402. We read revision -11 (25 September), the unsubmitted Budgets draft and TPX, probed the one named production deployment, and ran the draft's streaming cost trailer through 16 HTTP client setups. Nine never see it, including both OpenAI SDKs. The fallback formula overstates cost, and the default signature does not cover the request body that sets the price.
OpenAI says 'out of money' with a 429, Anthropic with a 400, 402 or 429, OpenRouter with a 402 that sometimes means 'wait'. The four official SDKs honor Retry-After up to anywhere from 60 seconds to 49 days, and x402 has no throttling signal at all. We read the IETF RateLimit draft, the x402 reference code and the SDK retry logic, then probed 1,951 x402 sellers: 8.6% publish a limit, 7 use the current syntax, and some count unpaid price checks against paid quota.
Between 18 and 25 September, 17 pull requests merged into x402. The sharpest was a Python paywall bypass: the middleware matched routes on the escaped path while the framework dispatched on the decoded one, so /api%2Fpremium reached a paid handler for free until all three SDKs shipped a fix on 22 September. The same week, a Lightning exact scheme merged that binds each invoice to a hash of the request it pays for, and Block joined the x402 Foundation. Also: Coinbase for Agents now pays x402 from Coinbase USDC balances with a 5 USDC cap and no payment-specific OAuth scope, and a BlackRock paper names x402 while citing Stripe's OpenRouter deal as a sign that model routing is becoming financial infrastructure.
Zodiac Roles lets a scoped key act for a Safe, but x402 pays with a signature, and a Roles member cannot sign for the Safe. We built two bridges on a Base fork with the unmodified x402 SDK: a daily top-up to a hot wallet, and an undocumented Roles library that makes the Safe sign only allowlisted USDC authorizations. The second one works, costs 475,823 gas per payment, spends budget at signing, and survives role revocation.
ERC-8183 is the proposed job escrow for agent commerce. The published EIP, its inline reference code and the reference repository define three incompatible fund() functions. On the live AgenticCommerceV3 contract on Base, 95% of completed volume was self-evaluated, 77% came from two addresses paying each other, and the admin able to pause refunds and withdraw escrow is a single EOA.
ANS anchors agent identity to DNS, ACME and a public transparency log, and GoDaddy runs it in production. We checked the signed checkpoint, an inclusion proof and a status token ourselves, then parsed all 351,912 events: 95.8% of registrations sit under one domain, 99.94% are v1.0.0, none carries an LEI, 0.18% publish TLSA, and a Zelle-named agent is still ACTIVE.
Every agent paying in USDC holds an asset with an off-switch. We counted it: 833 addresses ever listed on Ethereum, 639 still listed, 120.7M USDC immobilized, plus 469 on Base. Then we traced what x402 does when a payer is frozen — and found it maps to a generic simulation failure with no error code of its own.
Coinbase ships three different spend guards for agents: an in-process SDK ledger, a server-side policy engine, and Wallet MCP's per-transaction approval link. Only one of them is reachable from a chat surface, and it is the one that cannot do per-call micropayments. We read the primary sources and probed the endpoint.