x402 vs AP2 vs A2A-SE

These three protocols address different layers of the agent payment stack. They are complementary, not competing.

Quick Comparison

Concern	x402	AP2	A2A-SE
Payment negotiation	—	Yes	Lightweight
Access gating	Yes	—	—
Task escrow	—	—	Yes
Dispute resolution	—	—	Yes
Reputation	—	—	Yes
Multi-turn tasks	—	—	Yes

x402 — Access Gate

Question: "Can I talk to this agent?"

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

• Use case: Gate discovery, pay to unlock API access
• Flow: Request → 402 → Pay → 200 + content

AP2 — Payment Negotiation

Question: "How will we pay?"

AP2 (Agent Payments Protocol) handles payment negotiation — method selection, currency, amount. It defines flows for agents to agree on payment terms before work begins.

• Use case: "I want USDC." "I only accept ATE." → Negotiate
• Relationship: A2A-SE can use AP2 as upstream; AP2 negotiates, A2A-SE executes

A2A-SE — Task Escrow

Question: "How do we hold and release funds while the agent does multi-step work?"

A2A-SE provides escrow-based settlement for A2A tasks:

• Lock tokens before work

• Hold during execution (including multi-turn)

• Release on completion, refund on failure

• Dispute resolution, reputation, webhooks

• Use case: Contractor payment — hold funds, pay on delivery

Hybrid Flow

An agent can use all three:

Client                  Provider                    Exchange
  |                        |                           |
  |---x402 payment-------->|  (access gate)            |
  |<--200 + AgentCard------|                           |
  |                        |                           |
  |---POST /escrow---------|-------------------------->|  (lock funds)
  |---A2A message/send---->|                           |
  |       ...working...    |                           |
  |<--A2A task completed---|                           |
  |---POST /release--------|-------------------------->|  (settle)

When to Use What

• x402: You need to gate access to your agent behind a paywall
• AP2: You need complex payment negotiation (multiple currencies, methods)
• A2A-SE: You need escrow for task-based work (the core A2A use case)

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