Quick Take Layer 3 blockchains provide higher levels of customizability while retaining some level of security from layer 1 blockchains. Layer 3 blockchains can be built with recursive proving, compressing multiple validity proofs into one recursive proof. StarkWare, zkSync, Slush, Immutable and Sorare are some of the projects that have revealed plans relating to Layer 3s. Layer 3s would be better suited for application-specific purposes while providing reduced transaction costs for users.