Amazon Amazon This document describes an extension to the MLS protocol [RFC940] that improves its efficiency in terms of per-member download size. This comes at essentially no cost. In essence, this document defines a new message type called split commit which replaces regular MLS commits. Unlike regular commits, a split commit can be "split" by the Delivery Service (DS) into much smaller per-member commits, one for each receiving member. The size of a per-member commit is always logarithmic in the group size, while the size of a regular MLS commit can be linear. This extension works in settings with a DS that can do the splitting which can be demanding with encrypted MLS handshake messages. This is motivated by academic research [KKP22], [HKPPW22], [AHKM22].