Due to a nasty interaction between Unity's package compression and Steam's patch diff protocol, it seems steam is redownloading every package that has changed a single bit in each patch. This can make the downloads large. There are two possible solutions, but one might not be viable if unity doesn't allow package build options to fix it. Both solutions could be used together. 1. Reduce the number of assets per a package, and bundle together ones that will likely be both changed at once and loaded at once for both optimal patching and loading. 2. Place a compression barrier between assets so if one changes, the rest of the file remains identical by binary allowing it to utilize a proper binary patch file. To repeat myself, Unity probably doesn't allow handling the second option from the UI, but it might in the build scripts. It's probably highly undocumented and would require reading the technical documentation of the actual tools used to create the packages.