Payment + discovery
Binance B402 Bazaar
Capability descriptions, payment requirements, and service evidence mapped to B402 discovery.
P21 / INTEROPERABILITY
One protocol. Across systems.
Bitcoin-native evidence across agent frameworks, payment systems, and execution chains.
Compatibility specifications; released adapters are listed in implementation status. Implementation status
Payment + discovery
Coinbase CDP Bazaar
x402 service discovery with payment evidence kept separate from task verification.
Tool distribution
MCP Registry
Versioned tool contracts with explicit inputs, permissions, findings, and failure states.
Native evidence
TAP / DMT / Ordinals
Bitcoin-derived rules and asset evidence interpreted under native metaprotocol semantics.
Agent commerce
Virtuals ACP
Agent commerce records connected to independently evaluated service outcomes.
Evidence + coordination
Trac / OpenMayhem
Original signed receipts and source context carried across coordinated agent workflows.
Alternative payment adapters
PayAI / thirdweb
Provider-specific payment schemes mapped to a common evidence contract.
Financial agent tooling
OKX Onchain OS
Financial-action evidence bound to network, asset, recipient, and execution policy.
Communication + identity
A2A / ERC-8004
Agent communication and identity references alongside independent evidence evaluation.
Bitcoin payments
Lightning L402
Bitcoin-native service payments with authorization and verification kept separate.
External evidence + beacons
Chainlink / drand
External proofs and beacon sources with distinct verification and trust profiles.
Agent clients
Hermes / local agents
One evidence model across agent clients, local tooling, and service interfaces.
Independent systems. Shared evidence.
Each interface preserves its own payment, identity, and execution semantics. Proof21 provides the evidence contract between them.
Interface contracts ↗