Tutorials, comparisons and design patterns for building autonomous agents that self-fund, call 345+ models and orchestrate MCP Tools.
On EVM chains, x402 rides on EIP-3009 signatures. Solana has no transferWithAuthorization, so the exact SVM scheme takes a different route: the agent signs a real transaction minus one signature, and the facilitator co-signs as fee payer. We walk through the spec — instruction layout, fee-payer safety rules, memo nonces, and the replay window.
IP allowlists and User-Agent strings cannot authenticate autonomous agents. Web Bot Auth puts an Ed25519 signature on every request, publishes keys in a well-known directory, and now has an IETF working group behind it. We walk the wire format, the deployments at Cloudflare and AWS, and the point where verified identity meets x402 payment.
The Agentic Commerce Protocol from OpenAI and Stripe defines how ChatGPT buys goods on your behalf. We read the spec: the five checkout_sessions endpoints, the signed delegate_payment call that mints a scoped vault token, and Stripe's Shared Payment Token. Then we contrast its card-custodial model with x402's non-custodial stablecoin rail.
Payments week for autonomous agents: the Linux Foundation took over x402 with Visa, Mastercard, Stripe and Circle onboard; a Visa-Artemis report drew the line between card macro-commerce and stablecoin micro-commerce; Binance wired x402 into its agentic wallet; and Zscaler documented agents making crypto payments to attackers via prompt injection.
x402 moves the money; the Bazaar answers the prior question: which endpoint, at what price, with what schema? We read the CDP discovery layer end to end — settle-time indexing with no registration step, the three HTTP surfaces, the discovery MCP server, the seller and buyer SDK calls, and the cracks that still show.
x402 and EIP-3009 are single-chain settlement primitives. When an agent holds USDC on Base but the service wants it on Arbitrum, you need settlement mobility. CCTP V2 burns native USDC on the source chain and mints it on the destination, and Hooks let one transaction pay the service atomically on arrival. A technical read of depositForBurn, finality thresholds, and how it composes with x402.
The default agent wallet is an EOA, and an EOA key has one spending limit: everything. This is a deep dive into the on-chain layer that fixes it — ERC-4337 smart accounts, session keys, the ERC-7715/7710 permission standards, Coinbase Spend Permissions, paymasters that pay gas in USDC, and the asset-enforced spend mandate on the horizon.
A2A carries the message, AP2 shapes it, x402 settles it. The A2A x402 extension wires the three together with a five-state payment machine over the A2A Task lifecycle. We read the v0.1 spec: identifiers, data structures, metadata keys, and the security rules that keep private keys away from the model.