How AI Agents Pay: AP2, ACP, x402 and MPP Explained
Unhappy-Life8236 · reddit · 2026-10-02
A Reddit deep-dive breaks down the four protocols making up the emerging AI agent payment stack:
- AP2 handles authorization: humans set spending caps and issue a payment mandate that merchants record; nothing moves until it's approved.
- ACP handles checkout: agents pass the cart as structured data instead of clicking through web pages, still running on regular cards and payment networks with no merchant-side changes.
- x402 covers pay-per-request: the server returns a 402 status with a price tag, the agent's wallet signs a USDC transfer, then retries — no accounts or API keys needed, ideal for selling API hits.
- MPP handles high-frequency access: agents open a session, accumulate charges, and settle at the end, avoiding x402 overhead per request.
Typical flow: AP2 first for human approval, then one of ACP/x402/MPP completes payment. The author also flags an overlooked gap: protocols solve payment but not per-agent usage tracking and human-readable invoicing for sellers.
Related event: How AI Agents Pay: AP2, ACP, x402 and MPP Explained(2 posts)→
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