Still no diff patching support? I'm really sick of having to re-download 40 gigs every other day when an early-access game based on Unreal decides it needs to update.
Seriously, diff patching has been a thing for decades and we're in the age of artificially-restricted bandwidth allocation. If Unreal can't get with the times, then Unreal needs to go away and make room for engines that bother to use modern practices.
There are no other better engines and what's more, there only two serious competitors out there. CryEngine and Unity. CryEngine has nowhere near the amount of documentation UE has (both official and unofficial) and investing time into learning to work with CryEngine is questionable since the company behind it may go bakrupt at any time and the skills you'll learn are not really usable outside of your project(s) since pretty much no one in the industry (except CIG and Warhorse) uses it. Unity is great for what it is, but it's not exactly the best choice as far as ambitious projects go.
CIG switched to Amazon's Lumberyard fork of CryEngine, which I suspect will become the canonical upstream, provided Amazon keeps up it's support and doesn't alienate people with crazy Amazon service tie-ins. My (not very in-depth or researched) impression is that the original team at CryTek suffered a brain drain long before this latest round of financial difficulties (e.g. lead engineer Tiago Sousa moving to id Software to succeed John Carmack as lead renderer guy), so I suspect they don't have a huge the "real change is happening in this branch" advantage over Lumberyard anymore, and Amazon is surely more stable than CryTek is.
Note I'm not working inside this industry, this is just pieced together from news observation.
Steam does delta compression automatically and for most changes shouldn't be an issue.
UE4 has an append mode to add extra content in separate .pak, but if you are using Steam to distribute it doesn't save you anything. I believe it understands pak files enough to decompress, delta encode, then recompress.
Yeah, given how steam tends to fragment game files on disk, I figure Steam probably figures this stuff out for your game(unless we're talking about one of those games you can play before it's all there). If this is the case, I can see why they wouldn't bother adding it to the engine.
Unreal has had the ability for games to create patches (new exe and changed/additional content) for some time.
Distribution and application is generally the harder part of diff patching though and I suspect most early-access games prefer not to worry about it (though 40GB seems a bit further along than early access!)
Seriously, diff patching has been a thing for decades and we're in the age of artificially-restricted bandwidth allocation. If Unreal can't get with the times, then Unreal needs to go away and make room for engines that bother to use modern practices.