World Liberty Financial ($WLFI) has released AgentPay SDK v0.2.1, an update that extends its open-source AI agent payment toolkit to support x402 and MPP (Machine Payment Protocol) HTTP payment flows, while also expanding EIP-3009 signing support and adding Tempo mainnet compatibility.
What Is AgentPay SDK?
Think of AgentPay SDK as a wallet and payment system built specifically for AI agents, not humans.
When an AI agent is running a task, it often needs to pay for things along the way: pulling data from a paid API, accessing a service, or completing a machine-to-machine transaction. Without a purpose-built payment layer, that agent either can’t do the job or has to hand off control to an outside system to handle the money.
AgentPay solves that. It gives the agent its own wallet, a set of spending rules defined by the operator, and the ability to sign and send payments locally without contacting $WLFI or any third party. The agent can spend, but only within the boundaries the operator sets.
SDK stands for Software Development Kit, which is essentially a packaged set of tools developers use to build or extend software. In this case, the kit includes a command-line interface (CLI), a local signing daemon, a policy engine, and a skill pack that connects the wallet to agent hosts like Claude Code, Codex, and OpenClaw.
What Changed In AgentPay SDK v0.2.1?
The original AgentPay SDK, released around March 21, gave AI agents a local, self-custodial runtime for wallet setup, policy-based transfers, and human approval checkpoints. Version 0.2.1 builds on that foundation by letting agents pay for API access and HTTP-native services directly, without handing control away from the operator.
All transactions settle in $USD1, $WLFI‘s dollar-pegged stablecoin, which has roughly $4.4 billion in circulation according to DefiLlama.
What x402 Support Adds
The x402 flow handles HTTP 402 payment responses, a standard where an API signals that a resource requires payment before access is granted. With v0.2.1, AgentPay supports:
- Exact-payment and EIP-3009 x402 HTTP payment flows
- Reusable HTTP request controls including –method, repeatable –header, –data, and –json-body
The flow works like this: the agent requests a resource, the API responds with a 402 status and a price, AgentPay checks the operator’s spending policy, signs locally using EIP-3009, and retries with payment proof attached. The API then returns the data.
What MPP Support Adds
MPP (Machine Payment Protocol) introduces session-based payments on Tempo mainnet. Instead of paying per request, an agent can open a session, deposit funds, make multiple requests, and close out when the job is done.
New MPP features in v0.2.1 include:
- MPP HTTP 402 payments on Tempo mainnet
- Tempo session flows with session open, voucher signing, optional –deposit, automatic top-up, and explicit close
- Persisted session reuse via –session-state-file
- Decoded Payment-Receipt output plus JSON and NDJSON automation modes
How Does AgentPay Keep Operator Control Intact?
This is the core design question the SDK is built around. Every transaction, whether a simple transfer or a paid API call, runs through the same local policy engine before any signing takes place. There is no code path that bypasses policy enforcement.
The architecture spans four layers: a command-line interface (CLI), a local signing daemon, a policy engine, and a skill pack for integration with agent hosts like Claude Code, Codex, and OpenClaw. Private keys never leave the operator’s machine. $WLFI does not custody assets, access keys, or process funds.
When a transaction exceeds a preset threshold, the SDK pauses and requires human approval. If a wallet runs low on funds, the system halts the operation and returns an error with the wallet address, chain ID, and a QR code for replenishment.
The SDK charges no platform fees. Only standard blockchain gas fees apply. It is released under the MIT licence with no telemetry or auto-update mechanisms.
Who Is AgentPay SDK v0.2.1 Built For?
AgentPay targets developers building autonomous agents that need to pay for services during execution, such as paid APIs, data feeds, or machine-to-machine services, while keeping a human operator in control of how and when money moves. The macOS-first setup integrates with macOS Keychain and runs a root-managed LaunchDaemon locally.
Conclusion
AgentPay SDK v0.2.1 does one thing the original release could not: it lets AI agents pay for work in real time, mid-task, without the operator losing control of how that money moves.
The addition of x402 and MPP support means agents can now access paid APIs, data feeds, and HTTP-native services as part of their normal execution flow. Sessions can be opened, funded, used across multiple requests, and closed out, all within policy limits the operator defines upfront.
The core design has not changed. Keys stay local. Signing stays local. $WLFI has no access to wallets or funds. The only thing that has expanded is what the agent can do inside that controlled environment.
For developers building autonomous agents that interact with paid services, v0.2.1 closes a practical gap that the first release left open.
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World LibertyFi on X: Post on March 31
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World LibertyFi docs: About AgentPay SDK
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Report by The Defiant: World Liberty Financial Launches Toolkit to Let AI Agents Spend $USD1