Raspbian is the official Linux distribution of the Raspberry Pi products, and a new version has been released by its developers.
As the name indicates, Raspbian is based on Debian, but nothing that major happened to the base of the OS, with one exception. The developers did make a number of upgrades to the packages, as it was to be expected. Raspbian is stable, and the current iteration of the OS will be kept a little bit longer, but the devs need to upgrade packages in the OS.
Since Raspbian is one of the most used operating systems for the Raspberry Pi devices (all of them), it stands to reason that the team will pay a lot of attention to what comes by default, and that includes packages like Sonic Pi or Scratch.