An AI agent that pays for its own API calls on AWS

I built a small AWS Bedrock AgentCore agent that pays for a paywalled API with real USDC on Arbitrum One. It asks for a report, gets back HTTP 402 Payment Required, settles the charge on its own, and retries. No API key, no card on file, no human clicking approve. The settlement lands on Arbitrum One mainnet, and the run prints an Arbiscan link to the transaction so you can read it yourself.

There's a great walkthrough of the same idea on Base Sepolia by William Mendoza Gopar. This post expands upon his work: mainnet instead of testnet, real USDC instead of a burn-address demo, and a merchant built on CloudFront, Lambda@Edge, and API Gateway. The full source is at github.com/hummusonrails/arbitrum-x402-aws.

What AgentCore gives you

AgentCore is AWS's hosted runtime for AI agents, still in preview. The piece this project leans on is AgentCore Payments: a managed signer that holds an embedded wallet for you and produces payment authorizations on request. Your code asks the PaymentManager to handle a charge, and the private key stays inside AgentCore.

You stand up four resources once: a PaymentManager with a connector to Coinbase CDP, an embedded crypto wallet as a PaymentInstrument, and a PaymentSession that carries a spend budget and an expiry. After that, paying is a single call.

What x402 is

x402 puts the 402 Payment Required status code to work. A paid endpoint answers an unpaid request with 402 and a JSON body describing what it wants: the network, the token, the recipient, and the amount. The client signs an EIP-3009 transferWithAuthorization for USDC, which lets someone else submit the transfer on-chain, and resends the request with the signature attached. The server verifies and settles through a facilitator, then returns the content. No accounts to create, no keys to rotate, and charges as small as a fraction of a cent. That last property is what lets an agent use it with no human in the loop.

One aside on the AWS side: this x402 support is a brand-new preview release. This week I worked with the AWS team to make sure it settles across EVM chains, Arbitrum One included, so the wallet, the facilitator, and the settlement path behave the same way on Arbitrum as on any other EVM network.

Why Arbitrum One

An agent that pays per API call cannot spend a dollar in transaction fees to move a fraction of a cent. The math only works if the settlement layer makes sub-cent payments cheap enough to vanish into the cost of the call itself. Arbitrum One clears that bar on price.

Price is half of it. The other half is predictability.

An agent commits to a workflow and runs it; it cannot pause to renegotiate when gas spikes partway through. When fees jump for a few minutes, a person shrugs and waits, but an agent paying per call either overpays or stalls. Arbitrum's gas pricing is built to absorb those spikes. The recent Arbitrum One upgrade replaced the old single-target pricing model, and during peak activity it cut gas by around 98% compared to what that model would have charged. Fees stay low, and they stay close to where they were a minute ago. For x402 micropayments, that stability is worth as much as the headline number.

The shape of the demo

Three pieces talk to each other. The agent runs on AgentCore with its embedded CDP wallet. The merchant is an AWS stack: CloudFront in front, a Lambda@Edge function on viewer-request that speaks x402, and an API Gateway HTTP API with a Lambda behind it that holds the report. Settlement runs through the Coinbase CDP facilitator, which broadcasts the USDC transfer on Arbitrum One.

The round trip looks like this. The agent does a GET /report. Lambda@Edge sees no payment and returns 402 with the terms. The agent asks AgentCore to produce a payment for those terms and retries. This time Lambda@Edge has a payment header, calls the facilitator to verify and settle, and on success passes the request through to API Gateway, which returns the gated JSON.

The agent side

The agent code is short because the wallet logic lives in AgentCore. It makes a normal GET. If the response is anything other than 402, it returns it. If it is a 402, it hands the whole challenge, status, headers, and body, to generate_payment_header, which reads the terms, signs the authorization inside the embedded wallet, and returns the header to attach. Then it retries the GET.

def fetch_with_payment(*, client, payment_manager, url, user_id,
                       payment_instrument_id, payment_session_id):
    first = client.get(url)
    if first.status_code != 402:
        return first

    payment_required_request = {
        "statusCode": 402,
        "headers": dict(first.headers),
        "body": first.text,
    }
    proof_headers = payment_manager.generate_payment_header(
        user_id=user_id,
        payment_instrument_id=payment_instrument_id,
        payment_session_id=payment_session_id,
        payment_required_request=payment_required_request,
        network_preferences=["eip155:42161"],  # Arbitrum One
        client_token=str(uuid.uuid4()),
    )
    return client.get(url, headers=proof_headers)

I pass network_preferences=["eip155:42161"] so the payment targets Arbitrum One rather than relying on a default. The agent never builds EIP-712 typed data and never touches the private key. From the caller's point of view it made one GET and got back a 200 with the report and an Arbiscan link.

The merchant side

The payment logic sits in the Lambda@Edge function on viewer-request. With no payment header it returns the 402 and the accepts[] terms. With a header it decodes the payment, calls the CDP facilitator's /verify, then /settle, and returns the original request so CloudFront continues on to API Gateway. A verify or settle failure comes back as a fresh 402 or a 502.

One detail to note: CDP's facilitator uses short-lived JWTs that are bound to the exact request URL and method and expire in two minutes. You cannot mint one ahead of time and paste it into config. The edge function signs a fresh JWT with node:crypto for each verify and settle call, which is also why the CDP key material gets inlined into the edge bundle at build time (Lambda@Edge cannot read environment variables at runtime).

A design choice worth flagging: this version verifies and settles in viewer-request, before the origin responds. That keeps the demo to one function and one round trip. For production you want to verify in viewer-request and settle in viewer-response, so you only take the money after the content is delivered.

Funding it and running it

Setup is one command that creates the AgentCore resources and prints a wallet address. You fund that wallet with USDC on Arbitrum One, grant the agent signing permission, and paste the printed IDs into .env. Then:

$ make run-agent
GET https://<merchant>/report
  via AgentCore PaymentSession payment-session-...
  using Instrument            payment-instrument-...

Status: 200
Body:
{ ...gated report JSON... }

Arbiscan: https://arbiscan.io/tx/0x...

The agent requests the report, pays, and prints the JSON plus the transaction link. The whole round trip takes a few seconds, most of it the facilitator talking to the chain. The charge in the repo is 0.01 USDC per call.

Cost and the preview caveat

Idle, this costs close to nothing. CloudFront, Lambda@Edge, API Gateway, and AgentCore are billed per use, and the demo's traffic fits inside their free tiers. Per call you pay the 0.01 USDC settlement and a rounding error of compute.

AgentCore Payments is in preview, so treat it that way. Field names and SDK shapes can move between releases, and I hit a few of those while building this. Pin your versions and re-test after you upgrade.

Where this goes next

The same pattern extends in two directions worth trying. The agent can pay several different x402 endpoints with the same wallet and session, which makes it a buyer for any priced API it can reach. And the spend budget on the PaymentSession is the natural place to wire an alert or a hard stop, so an agent that misbehaves runs out of allowance instead of running up a bill.

Resources

Repo: github.com/hummusonrails/arbitrum-x402-aws
The Base Sepolia walkthrough by William: go to his blog
x402 protocol: x402.org
Bedrock AgentCore: aws.amazon.com/bedrock/agentcore
EIP-3009 (Transfer With Authorization): eips.ethereum.org/EIPS/eip-3009

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