x402 vs AP2 vs A2A-SE

These three protocols address different layers of agent commerce. They are complementary, not competing.

Thesis: AP2 authorizes the agent. A2A-SE ensures the agent actually did the work before the money settles. x402 moves or gates value at the edge.

Quick Comparison

Concern	x402	AP2	A2A-SE
Access gating	Yes	—	—
Spending authorization	—	Yes	Integrates
Payment / value movement	Micropayment	Negotiation	No (rail-agnostic)
Economic commitment / escrow	—	—	Yes
Dispute resolution	—	—	Yes
Reputation / finality	—	—	Yes
Multi-turn tasks	—	—	Yes

x402 — Access / value at the edge

Question: "Can I talk to this agent?" (or "pay to unlock this call")

x402 is a pay-per-call micropayment / access protocol. An agent behind an x402 gate returns HTTP 402 until the caller submits a micropayment. Think of it as a toll booth on the payment layer.

AP2 — Authorization

Question: "May this agent spend?"

AP2 (Agent Payments Protocol) focuses on authorization and payment negotiation — method selection, limits, and permission for an agent to initiate spend. It does not define whether work was completed before value reaches finality.

Relationship: AP2 authorizes. A2A-SE settles.

A2A-SE — Settlement

Question: "Was the obligation satisfied, and what happens to committed value?"

A2A-SE provides settlement semantics for A2A tasks:

Economic commitment (escrow or equivalent) before work
Hold during multi-turn execution
Release on verification, refund on failure
Disputes, reputation, auditability

Escrow is one mechanism; settlement is the abstraction.

Hybrid flow

Client                  Provider                    Exchange
  |                        |                           |
  |---x402 (optional)----->|  (access gate)            |
  |<--200 + AgentCard------|                           |
  |                        |                           |
  |---authorize (AP2)------|  (may the agent spend?)   |
  |---POST /escrow---------|-------------------------->|  (commit)
  |---A2A message/send---->|                           |
  |       ...working...    |                           |
  |<--A2A task completed---|                           |
  |---POST /release--------|-------------------------->|  (settle)

When to use what

x402: Gate access or collect per-call micropayments
AP2: Authorize and negotiate spend
A2A-SE: Settle task-based work with commitment, verification, and finality

Most A2A agents integrating settlement use A2A-SE directly. x402 and AP2 are optional adjacent layers.

Quick Comparison​

x402 — Access / value at the edge​

AP2 — Authorization​

A2A-SE — Settlement​

Hybrid flow​

When to use what​