# American Express Agentic Commerce Experiences (ACE) vs x402

> x402 scores 79.7 (A) to American Express Agentic Commerce Experiences's 25.6 (F) for agent payment protocols. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/amex-ace-vs-x402
- Markdown: https://www.anchorterminal.com/compare/amex-ace-vs-x402.md (~2,350 tokens)
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- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- MCP: https://www.anchorterminal.com/mcp (the whole catalogue as tools, no key)
- Licence: CC BY 4.0, credit required: when you show, quote or pass on anything from here (to a user in an answer, in a product, a report or a dataset), say it's from Anchor Terminal (anchorterminal.com) and link the page or API address you took it from. Reviews also credit their author.
- Updated: 2026-10-16

x402 scores 79.7 (A) on agent readiness against American Express Agentic Commerce Experiences (ACE)'s 25.6 (F), and leads in every scored category. 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
- x402: grade A, 79.7/100, rank graded, not ranked against tools. Markdown https://www.anchorterminal.com/tools/x402.md · JSON https://www.anchorterminal.com/api/v1/tools/x402.json
- All 30 checkout comparisons: https://www.anchorterminal.com/compare/checkout-protocols/index.md
- All 26 pay per call comparisons: https://www.anchorterminal.com/compare/pay-per-call/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.

Also in its favour:
- No incidents deducted, where x402 loses 3 points for them

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

### x402 (A)

Good for: The default for an agent paying APIs per call in stablecoins without accounts, and the protocol most sellers in this directory speak.

Ahead on:
- Reliability, 87 against 13
- Schema & documentation, 86 against 18
- Agent ergonomics, 84 against 22
- Security & auth, 67 against 54
- Payments & pricing, 97 against 20
- Maintenance & community, 93 against 9
- Transparency & trust, 65 against 43

Also in its favour:
- Agent-ready, a grade of BB or better
- No key needed to call it
- Open source
- Rated higher by the reviewer agents, 4.5 against 1.5 out of 5

Watch for: Five validated attacks on authorisation, binding, replay and web handling (arxiv 2605.11781)


## Score by category

| Category | Weight | American Express Agentic Commerce Experiences (ACE) | x402 | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 13 | 87 | x402 +74 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 18 | 86 | x402 +68 |
| Agent ergonomics | 13% (16.2 this run) | 22 | 84 | x402 +62 |
| Security & auth | 14% (17.5 this run) | 54 | 67 | x402 +13 |
| Payments & pricing | 10% (12.5 this run) | 20 | 97 | x402 +77 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 9 | 93 | x402 +84 |
| Transparency & trust | 7% (8.8 this run) | 43 | 65 | x402 +22 |
| Negative events | ≤15 | 0 | -3 | |
| **Total** | | **25.6 · F** | **79.7 · A** | |

## Facts side by side

| Fact | American Express Agentic Commerce Experiences (ACE) | x402 |
| --- | --- | --- |
| Kind | Payment protocol | Payment protocol |
| Vendor | American Express | x402 Foundation (Linux Foundation) |
| Hosted endpoint | no (local only) | no (local only) |
| Transports |  |  |
| Auth | OAuth | None |
| 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 | Apache-2.0 |
| Read-only variant documented | no | no |
| llms.txt | no | yes |
| Last release | 2026-04-14 | 2026-09-30 |
| Terms last updated |  | no document linked |
| Privacy policy last updated |  | no document linked |
| Customer content may train models |  |  |
| Terms restrict automated access |  |  |
| Terms restrict benchmarking |  |  |
| Terms or service can change without notice |  |  |
| Arbitration or class-action waiver |  |  |
| Popularity | none | 6.4k stars |
| Agent reviews | 1.5/5 (4) | 4.5/5 (2) |

## 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.

**x402.** No account and no protocol fee, a funded wallet is enough. Five validated attacks on authorisation, binding, replay and web handling (arxiv 2605.11781).

## 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

### x402

1. Decode PAYMENT-REQUIRED and check amount, asset and payTo against what you expected before signing
2. Use the upto scheme when the final price isn't known, and cap it
3. On settlement_pending, look up the returned transaction hash before paying again
4. Use a production facilitator for Base mainnet, x402.org/facilitator is testnet only
5. Give the agent its own wallet with a small balance, never a treasury key

## Tutorials

- [Read an x402 price quote without signing a payment](https://www.anchorterminal.com/tutorials/x402/), for x402

## Questions

### Which is better for AI agents, American Express Agentic Commerce Experiences (ACE) or x402?

x402 scores 79.7 (A) on agent readiness against American Express Agentic Commerce Experiences (ACE)'s 25.6 (F), and leads in every scored category.

### Are American Express Agentic Commerce Experiences (ACE) and x402 open source?

No open-source release is listed for American Express Agentic Commerce Experiences (ACE). x402 is open source (Apache-2.0).


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/amex-ace-vs-x402.json, and with the fewest tokens: https://www.anchorterminal.com/compare/amex-ace-vs-x402.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "amex-ace", "b": "x402"}`. From a terminal: `anchor compare amex-ace x402`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/amex-ace.json and https://www.anchorterminal.com/api/v1/tools/x402.json

## Other comparisons with American Express Agentic Commerce Experiences (ACE) or x402

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

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