The MSVC library has always been "source available" with Visual Studio, but I guess MS thought that they're very unlikely to actually make a profit from it[1] so they're giving it a permissive license instead.
[1] The "new MS" seems to delight a lot of people, but IMHO it's not all great; I'd much rather they not be "shedding" all this open-source stuff and kept selling software, if it meant they wouldn't stuff telemetry in everything they touch.
[1] The "new MS" seems to delight a lot of people, but IMHO it's not all great; I'd much rather they not be "shedding" all this open-source stuff and kept selling software, if it meant they wouldn't stuff telemetry in everything they touch.