A layer 2 is a protocol that provides users the ability to leave an offchain system if its operators go offline and also ensures that the operators of a system cannot cheat. Both of these assumptions need to be provable and enforced onchain.

Currently, Lightning is the only protocol in production that can meet this standard. But, there’s protocols that make different tradeoffs and can still provide users the ability to unilaterally exit. Unilateral exit means that a user can leave a system if its operators go offline.

Thus, the only offchain protocols that see users retain (a semblance) of custody are Lightning, Statechains, and implementations of Ark. These are systems where users enter a collaborative, 2-2 multisig with a counterparty or operator. If this entity goes offline, a user can exit any of these protocols with an L1 transaction.

There’s tradeoffs related to these systems, but ultimately a user can reclaim their funds onchain. That’s what makes them bitcoin native.