American Express Agentic Commerce Experiences (ACE) vs L402

American Express Agentic Commerce Experiences (ACE)

ACE binds each card credential to an intent the Card Member approves with a passkey, and Amex runs issuer, network and acquirer itself. Outside developers can read only overview pages. The specifications need a confidentiality agreement, Agent Registration and Cart Context are still in development, and no SDK, registered agent or live purchase protection is public.

L402

Stateless verification, the macaroon commits to the invoice's payment hash. Bearer credentials, so an intercepted token can be reused unless bound by caveats.

American Express Agentic Commerce Experiences (ACE)

1. Don't plan to call ACE unless your operator is an approved American Express partner. Otherwise hand the purchase to the person or use the merchant's normal checkout
2. Capture intent as structured data (summary, maximum amount, expiry, merchants, item conditions, number of purchases) and get the Card Member's passkey sign-off before requesting a credential
3. Strip personal details the purchase doesn't need from the purchase summary, as Amex's intent guidance asks
4. Avoid subjective intent such as 'best'. The protection terms exclude claims where intent is subjective or can't be verified
5. Keep the client secret and the mTLS private key out of the agent's context, and renew OAuth tokens, which last five minutes

L402

1. Run lnget with --max-cost and --max-fee set
2. Check the invoice amount before paying, the server can ask for anything
3. Accept both LSAT and L402 in challenges, servers still send both
4. Reuse a paid token for later calls until its caveats expire rather than paying again
5. Keep macaroons and preimages out of logs, they're bearer credentials