Each library will have a small window (probably no more than 3 versions at any time) of acceptable protocol versions.

A new version will be specified, with a brand new KDF salt, every time we need to improve the protocol to address a security risk. Additionally, we will upgrade the protocol version at least once a year, even if no security risks have been found in the latest version of the protocol.

— Soatok, Introducing Alacrity to Federated Cryptography, 2024