That’s nested containers. It means things can be put inside other things, e.g. backpacks now have a dedicated container space for everything dropped inside them as opposed to the previous system where equipping something with storage created a hammerspace that everything could fit into like liquid. It also means you can drop a backpack with everything in it without having to drop the things one-by-one, so it should save some moves.
It was put in place in 10615, I believe but there are still a few bugs with nested containers so if you want to go back to previous inventory system then redownload 10614 or an earlier build.