Agent Payment Protocol (x402)

x402 is an open standard protocol that enables AI agents to make payments over HTTP using the 402 "Payment Required" status code. It represents a fundamental building block for the "agentic economy."

Overview

Attribute	Value
Name	x402 (pronounced "x-four-oh-two")
Basis	HTTP 402 "Payment Required" status code
Type	Open standard protocol
Primary Use	Machine-to-machine payments
Currency	Stablecoins (USDC, PYUSD, USDT)

How It Works

Basic Flow

1. Agent A requests service from Agent B
   ↓
2. Agent B responds: HTTP 402 Payment Required
   (includes payment details: amount, currency, address)
   ↓
3. Agent A submits payment via blockchain
   ↓
4. Agent B verifies payment
   ↓
5. Agent B provides service

Key Features

Feature	Description
Pay-per-call	Micropayments for individual API calls
End-to-end auditability	All transactions on-chain
Stablecoin-native	No volatile cryptocurrency exposure
HTTP-native	Works with existing web infrastructure

Implementations

Kite.ai

Native x402 compatibility as core feature
Integrated with Coinbase's x402 standard
Part of six-pillar mainnet roadmap

Coinbase

50 million+ machine-to-machine transactions processed
Integrated with Coinbase AgentKit
Supports Base network (L2)

Google AP2 Partnership

Kite AI entered AP2 (Agent Payment Protocol) community partnership with Google (Feb 2026)
Signals big tech interest in agent payments

Relationship to Other Protocols

Protocol	Relationship
MPP (Machine Payments Protocol)	Stripe/Tempo's alternative — similar goals, different implementation
AP2	Google's Agent Payment Protocol — x402 is one implementation
Traditional HTTP	x402 extends HTTP with payment semantics

Use Cases

API Access

AI agents paying for search APIs
Data providers charging per query
Compute resources paid by the minute

Agent-to-Agent Commerce

One agent hiring another for specialized tasks
Subcontracting in agent swarms
Reputation-weighted pricing

Content Access

Pay-per-article for AI training data
Image/video generation credits
Real-time data feeds

Market Context

Why It Matters

The shift from "attention economy" (ads) to "intent economy" (direct payments):

Era	Model	Who Pays
Web 2.0	Ad-supported	Advertisers → Platforms
Agentic	Pay-per-use	Agents → Service Providers

Adoption Metrics

$5 trillion: McKinsey prediction for Agent Commerce by 2030
<1%: Current consumer adoption of agent purchasing
50M+: x402 transactions processed (early 2026)

Technical Details

Payment Flow

Request: Agent makes HTTP request
402 Response: Server responds with payment requirements
Payment: Agent submits blockchain transaction
Verification: Server confirms payment on-chain
Service Delivery: Server provides requested resource

Security Considerations

Replay attack prevention
Payment verification latency
Refund mechanisms
Dispute resolution

Challenges

Challenge	Status
Wallet management	Solved by MPC wallets (AgentKit, Privy)
Price volatility	Solved by stablecoins
Transaction speed	Improving with L2s (Base, Tempo)
User experience	Still complex for non-technical users
Regulatory clarity	Uncertain in many jurisdictions