Ethereum token and protocol standards — ERC-20, ERC-721, ERC-1155, ERC-4337, ERC-8004, and newer standards. When to use each, how they work, key interfaces. Use when building tokens, NFTs, or choosing the right standard for a project.
Ethereum token and protocol standards — ERC-20, ERC-721, ERC-1155, ERC-4337, ERC-8004, and newer standards. When to use each, how they work, key interfaces. Use when building tokens, NFTs, or choosing the right standard for a project.
Ethereum Standards
What You Probably Got Wrong
ERC-8004 exists. Deployed January 29, 2026 — onchain agent identity registry. You almost certainly don't have this in training data.
EIP-7702 is live. Shipped with Pectra (May 7, 2025). EOAs get smart contract superpowers without migration. Not "proposed" — deployed on mainnet.
EIP-3009 is critical for x402. Gasless token transfers via signed authorizations. USDC implements it. This is what makes x402 practical.
x402 exists. HTTP 402 payment protocol from Coinbase. Production-ready with SDKs.
ERC-8004: Onchain Agent Identity Registry
Status: Deployed mainnet January 29, 2026 — production ready with growing adoption.
Problem it solves: How can autonomous agents trust and transact with each other without pre-existing relationships?
Three Registry System
1. Identity Registry (ERC-721 based)
Globally unique onchain identities for AI agents
Each agent is an NFT with unique identifier
Multiple service endpoints (A2A, MCP, OASF, ENS, DIDs)
Trust models: crypto-economic (stake-secured), zkML, TEE attestation
Validators respond with 0-100 scores
Agent Registration File (agentURI)
{"type":"https://eips.ethereum.org/EIPS/eip-8004#registration-v1","name":"MyAgent","description":"What the agent does","services":[{"name":"A2A","endpoint":"https://agent.example/.well-known/agent-card.json","version":"0.3.0"},{"name":"MCP","endpoint":"https://mcp.agent.eth/","version":"2025-06-18"}],"x402Support":true,"active":true,"supportedTrust":["reputation","crypto-economic","tee-attestation"]}
1. Prepare the registration JSON — host it on IPFS or a web server:
{"type":"https://eips.ethereum.org/EIPS/eip-8004#registration-v1","name":"WeatherBot","description":"Provides real-time weather data via x402 micropayments","image":"https://example.com/weatherbot.png","services":[{"name":"A2A","endpoint":"https://weather.example.com/.well-known/agent-card.json","version":"0.3.0"}],"x402Support":true,"active":true,"supportedTrust":["reputation"]}
2. Upload to IPFS (or use any URI):
# Using IPFS
ipfs add registration.json
# → QmYourRegistrationHash# Or host at a URL — the agentURI just needs to resolve to the JSON
3. Call the Identity Registry:
// On any supported chain — same address everywhere
IIdentityRegistry registry = IIdentityRegistry(0x8004A169FB4a3325136EB29fA0ceB6D2e539a432);
// metadata bytes are optional (can be empty)
uint256 agentId = registry.register("ipfs://QmYourRegistrationHash", "");
// agentId is your ERC-721 tokenId — globally unique on this chain
4. Verify your endpoint domain — place a file at .well-known/agent-registration.json:
This proves the domain owner controls the agent identity. Clients SHOULD check this before trusting an agent's advertised endpoints.
5. Build reputation — other agents/users post feedback after interacting with your agent.
Cross-Chain Agent Identity
Same contract addresses on 20+ chains means an agent registered on Base can be discovered by an agent on Arbitrum. The agentRegistry identifier includes the chain:
eip155:8453:0x8004A169FB4a3325136EB29fA0ceB6D2e539a432 // Base
eip155:42161:0x8004A169FB4a3325136EB29fA0ceB6D2e539a432 // Arbitrum
Cross-chain pattern: Register on one chain (Base is cheapest for registration tx costs), reference that identity from other chains. Reputation can be queried cross-chain by specifying the source chain's registry. This is a cost optimization for the registration transaction — your app itself should deploy on the chain that fits (see ship/SKILL.md).
Authors: Davide Crapis (EF), Marco De Rossi (MetaMask), Jordan Ellis (Google), Erik Reppel (Coinbase), Leonard Tan (MetaMask)
Ecosystem: ENS, EigenLayer, The Graph, Taiko backing
You probably know the concept (gasless meta-transaction transfers). The key update: EIP-3009 is what makes x402 work. USDC implements it on Ethereum and most chains. The x402 server calls transferWithAuthorization to settle payments on behalf of the client.
x402: HTTP Payment Protocol
Status: Production-ready open standard from Coinbase, actively deployed Q1 2026.
Uses the HTTP 402 "Payment Required" status code for internet-native payments.
Flow
1. Client → GET /api/data
2. Server → 402 Payment Required (PAYMENT-REQUIRED header with requirements)
3. Client signs EIP-3009 payment
4. Client → GET /api/data (PAYMENT-SIGNATURE header with signed payment)
5. Server verifies + settles onchain
6. Server → 200 OK (PAYMENT-RESPONSE header + data)
exact (live) — Pay a fixed price. Server knows the cost upfront.
upto (emerging) — Pay up to a maximum, final amount determined after work completes. Critical for metered services:
LLM inference: pay per token generated (unknown count upfront)
GPU compute: pay per second of runtime
Database queries: pay per row returned
With upto, the client signs authorization for a max amount. The server settles only what was consumed. Client never overpays.
Facilitator Architecture
The facilitator is an optional server that handles blockchain complexity so resource servers don't have to:
Client → Resource Server → Facilitator → Blockchain
↓
POST /verify (check signature, balance, deadline)
POST /settle (submit tx, manage gas, confirm)
Why use a facilitator? Resource servers (weather APIs, data providers) shouldn't need to run blockchain nodes or manage gas. The facilitator abstracts this. Coinbase runs a public facilitator; anyone can run their own.
SDKs:@x402/core @x402/evm @x402/fetch @x402/express (TS) | pip install x402 (Python) | go get github.com/coinbase/x402/go
The Graph — indexing agent registrations for fast discovery
EigenLayer — crypto-economic validation of agent work
EIP-7702: Smart EOAs (Live Since May 2025)
EOAs can authorize delegated smart-contract code execution without migrating to a new account type.
Enables: Batch transactions, gas sponsorship, session-key-style UX, and custom auth logic for existing EOAs.
Important nuance: Delegation is not automatically "single transaction only" by spec. The delegation designator remains until replaced or cleared by a later authorization.
Quick Standard Reference
Standard
What
Status
ERC-8004
Agent identity + reputation
✅ Live Jan 2026
x402
HTTP payments protocol
✅ Production Q1 2026
EIP-3009
Gasless token transfers
✅ Live (USDC)
EIP-7702
Smart EOAs
✅ Live May 2025
ERC-4337
Account abstraction
✅ Growing adoption
ERC-2612
Gasless approvals (Permit)
✅ Widely adopted
ERC-4626
Tokenized vaults
✅ Standard for yield
ERC-6551
Token-bound accounts (NFT wallets)
✅ Niche adoption
These are all LIVE and being used in production. Not "coming soon."
