Agents now spend money. They pay for metered API calls, lease compute, buy data, and pull in services from all over the web. The one economic step they cannot finish on their own is paying. A person still has to set up billing ahead of time, distribute API keys, or sign off on each charge.

Opus Protocol removes that dependency. It gives machines recurring-payment infrastructure: a single on-chain mechanism that handles both one-off charges and ongoing subscriptions, available to any agent, with every record visible to the public. Payments settle on Robinhood Chain. That chain is an Arbitrum Orbit Ethereum L2 built for ~100ms block times, so in practice the sequencer confirms almost instantly and each transaction costs well below a cent.

Who it is for

Agent developers rely on Opus Protocol so their agents can pay without supervision. The agent reads pricing from whatever compatible service it finds, commits on-chain to a subscription, and no human has to answer a billing question afterwards.

Service providers adopt Opus Protocol as a billing layer where agent traffic is a first-class customer. You publish a pricing plan to the chain, place a middleware gate ahead of your API, and bill agents and people through one entry point. There are no keys to hand out and no invoices to chase.

Key capabilities

Capability	Description
One-time payments	Charges per request, settled over the x402-compatible flow
Subscription plans	Listed in an on-chain catalog and renewed automatically
Allowances	Spending grants with a cap, used to meter usage-based billing
Payment sessions	Tokens that cover high-frequency traffic and settle in batches (available at GA)
Webhooks	Lifecycle events delivered to your infrastructure as they happen

How it works

A provider publishes pricing plans to the Opus Protocol Plan Registry, which lives on-chain. When an agent asks for a paid resource, the response is 402 Payment Required carrying the plan’s terms. The SDK reads them and authorizes the payment (or the subscription) on-chain, after which the resource comes back. The chain then keeps the record, and either party can check it.

The Architecture page follows this flow through each layer.

What Opus Protocol does not do

A wallet, a token, a blockchain of its own: Opus Protocol is none of these. It is a billing layer that runs on top of the wallets, stablecoins, and services you already use. Think of it as closer to Stripe than to an L1.

Standards compatibility

Opus Protocol implements x402 natively. Coinbase introduced this HTTP payment protocol in May 2025; the x402 Foundation now stewards it under the Linux Foundation, and its participants include AWS, Circle, Google, Mastercard, Microsoft, Shopify, Stripe, and Visa. Opus Protocol is compatible with MPP (Machine Payments Protocol) as well, the IETF-tracked standard that Stripe and Tempo published in March 2026. See x402 Compatibility and MPP Compatibility for the details.

Get started

If you want an agent to pay for services:

1. Follow the Quickstart
2. Add the Agent SDK
3. Read up on Plans and Subscriptions

If you want to charge agents for something you run:

1. Follow the Quickstart
2. Add the Provider SDK
3. Publish a plan, then gate your API with the payment middleware

Beta scope

Opus Protocol is currently in public beta, running on Robinhood Chain mainnet. The beta includes the TypeScript SDK, the Opus Protocol Dashboard, subscription plans, fixed allowances, and one-time payments through the x402 flow. USDG is the only settlement asset. While the beta runs, Opus Protocol itself operates the Facilitator as a single centralized service.

The protocol fee on a one-time payment is 0.5% of the transaction value. Each settled subscription billing cycle carries a 0.3% fee, and sessions carry a fee of 0.2% of session volume. During the beta there is no fee for publishing to the Plan Registry.

A Python SDK, payment sessions, cross-chain settlement, support for additional stablecoins, and the decentralized facilitator network are planned for general availability and later.