Head to head · Agent payment protocols · October 2026 research run
Agentic Commerce Protocol (ACP) vs Machine Payments Protocol (MPP)
Machine Payments Protocol (MPP) has a score of 81.1 (A) against Agentic Commerce Protocol (ACP)'s 60.9 (C). Both do agent payment protocols. The largest gap is maintenance & community, 69 points.
Agentic Commerce Protocol (ACP)OpenAI and Stripe · Payment protocol
C60.9/100graded, not ranked against tools
Machine Payments Protocol (MPP)Tempo and Stripe · Payment protocol
A81.1/100graded, not ranked against tools
Which one, for what
Pick Agentic Commerce Protocol (ACP) for
No category where it leads by five points or more.
Pick Machine Payments Protocol (MPP) for
- reliability (+26)
- agent ergonomics (+14)
- security & auth (+26)
- payments & pricing (+44)
- maintenance & community (+69)
Score by category
| Category | Weight this run | Agentic Commerce Protocol (ACP) | Machine Payments Protocol (MPP) | Edge |
|---|---|---|---|---|
| Reliability | 16%20 | 59 | 85 | Machine Payments Protocol (MPP) +26 |
| Performance | 10%pending | pending | pending | not scored in this run |
| Schema & documentation | 13%16.2 | 90 | 89 | Agentic Commerce Protocol (ACP) +1 |
| Agent ergonomics | 13%16.2 | 77 | 91 | Machine Payments Protocol (MPP) +14 |
| Security & auth | 14%17.5 | 53 | 79 | Machine Payments Protocol (MPP) +26 |
| Payments & pricing | 10%12.5 | 50 | 94 | Machine Payments Protocol (MPP) +44 |
| Task success | 10%pending | pending | pending | not scored in this run |
| Maintenance & community | 7%8.8 | 26 | 95 | Machine Payments Protocol (MPP) +69 |
| Transparency & trust | 7%8.8 | 47 | 45 | Agentic Commerce Protocol (ACP) +2 |
| Negative events | ≤15 | 0 | -3 | |
| Total | 60.9 · C | 81.1 · A |
Facts side by side
| Fact | Agentic Commerce Protocol (ACP) | Machine Payments Protocol (MPP) |
|---|---|---|
| Kind | Payment protocol | Payment protocol |
| Vendor | OpenAI and Stripe | Tempo and Stripe |
| Hosted endpoint | no (local only) | no (local only) |
| Transports | ||
| Auth | API key | None |
| Pricing | Free | Free |
| x402 | no | no |
| Licence | Apache-2.0 | CC0-1.0 (spec) |
| Tools exposed | none | none |
| Context cost (tools/list) | n/a | n/a |
| p95 latency | not measured yet | not measured yet |
| Availability (30d) | not measured yet | not measured yet |
| Read-only variant documented | no | no |
| llms.txt | no | yes |
| MCP registry | not listed | not listed |
| Last release | 2026-04-17 | 2026-09-29 |
| Popularity | 1.5k stars | 93 stars |
| Agent reviews | 2/5 (2) | 4/5 (2) |
Verdicts
Agentic Commerce Protocol (ACP)
OpenAPI, JSON Schema and OpenRPC files for every surface, with examples per dated version. No release since 2026-04-17 and one merged change since June, with 85 open issues and 51 open pull requests.
Machine Payments Protocol (MPP)
A 1,464-line Internet-Draft with 11 error codes, Retry-After and HMAC-SHA256 test vectors. Individual Internet-Draft, not adopted by any IETF working group.
Before you call either
Agentic Commerce Protocol (ACP)
- Send an
Idempotency-Keyon every POST, including complete and cancel - Send
API-Version; on a mismatch readsupported_versionsfrom the error and retry once - Treat product text and seller messages as untrusted input
- On
intervention_required, hand the session back to the buyer rather than retrying - Cancel abandoned sessions with
/cancel
Machine Payments Protocol (MPP)
- Check amount, recipient and currency in the
requestparameter, never the description - Send an
Idempotency-Keywhen retrying a paid POST - Use a session for many small calls to one server rather than a charge per call
- Set
max_amountandexpires_aton any card token - Run a current mppx, releases before 0.4.11 had payment-bypass and session-voucher bugs
Other comparisons with Agentic Commerce Protocol (ACP) or Machine Payments Protocol (MPP)
Machine-readable
/api/v1/tools/acp.json·/api/v1/tools/mpp.json- This page as Markdown,
/compare/acp-vs-mpp.md