Contract Addresses & Protocol References

Deployed contract addresses for ERC-8004 agent identity registries and x402 facilitator endpoints on Base

Reference addresses and endpoints for the protocols that power agent identity and payments on Base.

ERC-8004 Agent Registry

ERC-8004 is a deployed onchain protocol with two smart contracts: the Identity Registry (ERC-721 NFT registry where agents register their identity) and the Reputation Registry (feedback and trust signals).

Base Mainnet

Contract	Address
Identity Registry	0x8004A169FB4a3325136EB29fA0ceB6D2e539a432
Reputation Registry	0x8004BAa17C55a88189AE136b182e5fdA19dE9b63

Base Sepolia (Testnet)

Contract	Address
Identity Registry	0x8004A818BFB912233c491871b3d84c89A494BD9e
Reputation Registry	0x8004B663056A597Dffe9eCcC1965A193B7388713

These are the canonical registry addresses shared across all ERC-8004 deployments on Base. The same addresses are used by 8004scan.io, the Agent0 SDK, and SIWA.

ERC-8004 contracts on GitHub →

ERC-8128 Request Signing

ERC-8128 is a cryptographic signing standard for HTTP messages — not a deployed smart contract. It defines how agents sign each request using their Ethereum key (EOA via ECDSA, or smart contract accounts via ERC-1271), and how servers verify those signatures.

There is no contract address to deploy or configure. The standard operates entirely through the HTTP headers Signature-Input, Signature, and Content-Digest. Smart contract account verification uses the standard ERC-1271 isValidSignature interface already present on deployed accounts.

ERC-8128 specification →

x402 Payment Facilitators

x402 facilitators are off-chain services, not a single smart contract. A facilitator verifies payment payloads submitted by clients and settles payments onchain on behalf of servers. Multiple independent facilitators operate on Base.

Coinbase CDP Facilitator (recommended)

The Coinbase facilitator is the default for most integrations and requires a CDP API key:

API endpoint	https://api.cdp.coinbase.com/platform/v2/x402
Verify path	POST /v2/x402/verify
Settle path	POST /v2/x402/settle
Networks	Base, Solana
Auth	CDP API key required

CDP x402 facilitator docs →

Public Testnet Facilitator

For development and testing without a CDP API key:

API endpoint	https://www.x402.org/facilitator
Auth	None required

Third-party Facilitators

Multiple third-party facilitators run on Base mainnet with varying network support and fee structures. See the x402 ecosystem page for the current list.

Protocol summary

Protocol	Type	What it does
ERC-8004	Deployed smart contract	Onchain NFT registry mapping agents to public keys and endpoints
ERC-8128	Cryptographic standard	Per-request HTTP message signing using Ethereum keys — no contract
x402	Off-chain service + USDC transfers	Facilitates pay-per-request stablecoin payments between agents and services

Related guides

Identity with SIWA

Register your agent in the ERC-8004 registry and verify requests with ERC-8128.

x402 payments

Let your agent pay for API access with stablecoins using the x402 protocol.