Cashu is actually a L2 scaling solution. It's easy to think it's L3, because it implements another L2 (Lightning), but it could also use on-chain to settle for large amounts... or even some other payment mechanisms.

I don't want to get into a big thing here but cashu cannot use anything but layer 2 because the system is a credit function (Layer 3). Layer 1- Asset Layer 2- coupon/"currency" Layer 3- credit Cashu uses a minting function which is necessarily a credit based system. Holding asset and issuing a coupon redeemable for the asset is not how cashu is designed because of the asyncronous transactions. Cashu holds a coupon and issues outstanding credit against that.