We support ArbOS 40 “Callisto” because it prepares us for Ethereum’s upcoming Pectra upgrade in a straightforward way. It lets EOAs run smart contract code (EIP-7702), boosts our cryptographic operations with enhanced BLS support (EIP-2537), and extends access to historical block data (EIP-2935), along with a minor Stylus caching fix. Honestly, there’s not much more to add, it’s a clean, necessary upgrade.