Proxy implementation, Arbitrum. Find the implementation behind a proxy contract on Arbitrum One: reads the EIP-1967 implementation, beacon and admin slots, EIP-1822 (UUPS), the older OpenZeppelin layout and EIP-1167 minimal-proxy bytecode, and names the kind found. Use before trusting or decoding a contract whose code can be swapped by its admin; for a fuller risk verdict use contract_risk. A malformed address is 400; an address without code is 404, both uncharged.