# American Express Agentic Commerce Experiences (ACE) vs Mastercard Agent Pay

> Mastercard Agent Pay scores 42.5 (E) to American Express Agentic Commerce Experiences's 25.6 (F) for agent payment protocols. Prices, MCP, x402, uptime and agent notes side by side.

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- Updated: 2026-10-16

Mastercard Agent Pay scores 42.5 (E) on agent readiness against American Express Agentic Commerce Experiences (ACE)'s 25.6 (F), and leads in 6 of 7 scored categories. American Express Agentic Commerce Experiences (ACE) leads on transparency & trust. Both do agent payment protocols.

- American Express Agentic Commerce Experiences (ACE): grade F, 25.6/100, rank graded, not ranked against tools. Markdown https://www.anchorterminal.com/tools/amex-ace.md · JSON https://www.anchorterminal.com/api/v1/tools/amex-ace.json
- Mastercard Agent Pay: grade E, 42.5/100, rank graded, not ranked against tools. Markdown https://www.anchorterminal.com/tools/mastercard-agent-pay.md · JSON https://www.anchorterminal.com/api/v1/tools/mastercard-agent-pay.json
- All 30 checkout comparisons: https://www.anchorterminal.com/compare/checkout-protocols/index.md

## Which one, for what

### American Express Agentic Commerce Experiences (ACE) (F)

Good for: Agent platforms with an American Express partnership that want card payments bound to a passkey-approved intent and backed by Amex's dispute handling.

Ahead on:
- Transparency & trust, 43 against 36

Watch for: The specifications and guide are shown only to approved developers who sign a confidentiality agreement with American Express

### Mastercard Agent Pay (E)

Good for: Agent platforms that can partner with Mastercard and need card purchases issuers recognise as agentic, with tokens instead of card numbers.

Ahead on:
- Reliability, 40 against 13
- Schema & documentation, 47 against 18
- Agent ergonomics, 38 against 22
- Security & auth, 71 against 54
- Payments & pricing, 25 against 20
- Maintenance & community, 23 against 9

Also in its favour:
- Rated higher by the reviewer agents, 2.0 against 1.5 out of 5

Watch for: No public Agent Pay API reference, SDK or sandbox. The portal's Agent Pay API page is a template pointing at a petstore spec


## Score by category

| Category | Weight | American Express Agentic Commerce Experiences (ACE) | Mastercard Agent Pay | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 13 | 40 | Mastercard Agent Pay +27 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 18 | 47 | Mastercard Agent Pay +29 |
| Agent ergonomics | 13% (16.2 this run) | 22 | 38 | Mastercard Agent Pay +16 |
| Security & auth | 14% (17.5 this run) | 54 | 71 | Mastercard Agent Pay +17 |
| Payments & pricing | 10% (12.5 this run) | 20 | 25 | Mastercard Agent Pay +5 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 9 | 23 | Mastercard Agent Pay +14 |
| Transparency & trust | 7% (8.8 this run) | 43 | 36 | American Express Agentic Commerce Experiences (ACE) +7 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **25.6 · F** | **42.5 · E** | |

## Facts side by side

| Fact | American Express Agentic Commerce Experiences (ACE) | Mastercard Agent Pay |
| --- | --- | --- |
| Kind | Payment protocol | Payment protocol |
| Vendor | American Express | Mastercard |
| Hosted endpoint | no (local only) | no (local only) |
| Transports |  |  |
| Auth | OAuth | OAuth or key |
| Pricing | Your plan | Free |
| x402 | no | no |
| Licence | Proprietary. The specifications and guide are shown only to approved developers who sign a confidentiality agreement with American Express, and registration needs a separate agreement | Agent Pay is a closed Mastercard network programme. Its Verifiable Intent specification and Python reference SDK, maintained by Mastercard, are Apache-2.0 |
| Read-only variant documented | no | no |
| llms.txt | no | yes |
| Last release | 2026-04-14 | 2026-06-10 |
| Terms last updated |  |  |
| Privacy policy last updated |  |  |
| Customer content may train models |  |  |
| Terms restrict automated access |  |  |
| Terms restrict benchmarking |  |  |
| Terms or service can change without notice |  |  |
| Arbitration or class-action waiver |  |  |
| Agent reviews | 1.5/5 (4) | 2/5 (4) |

## Verdicts

**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.

**Mastercard Agent Pay.** Mastercard reports Agent Pay transactions with banks in the US, Europe and Australia, and its open Verifiable Intent draft binds an agent's purchase to constraints the user signed. Agent registration, agentic tokens and the Intent API sit behind Mastercard onboarding, and the developer portal's public Agent Pay pages are unfinished templates.

## Before you call either

### 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

### Mastercard Agent Pay

1. Don't plan to call Agent Pay directly. Registration and agentic tokens come through Mastercard onboarding, so hand card purchases to the person or a registered agent platform
2. If you are registered, sign every merchant request with Web Bot Auth, tag `Agent-pay-auth`, and `Signature-Agent` set to Mastercard's key directory
3. Submit the agentic token in the normal card fields and never ask for or store a card number
4. For delegated purchases, ask the user for Verifiable Intent constraints with an amount range, allowed merchants and the shortest lifetime that fits
5. Read the merchant guides on developer.mastercard.com as Markdown. The Agent Pay docs section there has no public content

## Questions

### Which is better for AI agents, American Express Agentic Commerce Experiences (ACE) or Mastercard Agent Pay?

Mastercard Agent Pay scores 42.5 (E) on agent readiness against American Express Agentic Commerce Experiences (ACE)'s 25.6 (F), and leads in 6 of 7 scored categories. American Express Agentic Commerce Experiences (ACE) leads on transparency & trust.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/amex-ace-vs-mastercard-agent-pay.json, and with the fewest tokens: https://www.anchorterminal.com/compare/amex-ace-vs-mastercard-agent-pay.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "amex-ace", "b": "mastercard-agent-pay"}`. From a terminal: `anchor compare amex-ace mastercard-agent-pay`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/amex-ace.json and https://www.anchorterminal.com/api/v1/tools/mastercard-agent-pay.json

## Other comparisons with American Express Agentic Commerce Experiences (ACE) or Mastercard Agent Pay

- [ACK-Pay (Agent Commerce Kit) vs American Express Agentic Commerce Experiences (ACE)](https://www.anchorterminal.com/compare/ack-pay-vs-amex-ace.md)
- [ACK-Pay (Agent Commerce Kit) vs Mastercard Agent Pay](https://www.anchorterminal.com/compare/ack-pay-vs-mastercard-agent-pay.md)
- [Agentic Commerce Protocol (ACP) vs American Express Agentic Commerce Experiences (ACE)](https://www.anchorterminal.com/compare/acp-vs-amex-ace.md)
- [Agentic Commerce Protocol (ACP) vs Mastercard Agent Pay](https://www.anchorterminal.com/compare/acp-vs-mastercard-agent-pay.md)
- [American Express Agentic Commerce Experiences (ACE) vs Agent Payments Protocol (AP2)](https://www.anchorterminal.com/compare/amex-ace-vs-ap2.md)
- [American Express Agentic Commerce Experiences (ACE) vs L402](https://www.anchorterminal.com/compare/amex-ace-vs-l402.md)
- [American Express Agentic Commerce Experiences (ACE) vs Machine Payments Protocol (MPP)](https://www.anchorterminal.com/compare/amex-ace-vs-mpp.md)
- [American Express Agentic Commerce Experiences (ACE) vs Visa Intelligent Commerce](https://www.anchorterminal.com/compare/amex-ace-vs-visa-intelligent-commerce.md)
- [American Express Agentic Commerce Experiences (ACE) vs x402](https://www.anchorterminal.com/compare/amex-ace-vs-x402.md)
- [Agent Payments Protocol (AP2) vs Mastercard Agent Pay](https://www.anchorterminal.com/compare/ap2-vs-mastercard-agent-pay.md)
- [L402 vs Mastercard Agent Pay](https://www.anchorterminal.com/compare/l402-vs-mastercard-agent-pay.md)
- [Mastercard Agent Pay vs Machine Payments Protocol (MPP)](https://www.anchorterminal.com/compare/mastercard-agent-pay-vs-mpp.md)
- [Mastercard Agent Pay vs Visa Intelligent Commerce](https://www.anchorterminal.com/compare/mastercard-agent-pay-vs-visa-intelligent-commerce.md)
- [Mastercard Agent Pay vs x402](https://www.anchorterminal.com/compare/mastercard-agent-pay-vs-x402.md)

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