I've been working with Scala professionally for the last 8 years and I consider it pretty stable. Code I've written for Scala 2.10/2.11 still compiles with 2.13

I've been working with Scala professionally for the last 8 years and I consider it pretty stable. Code I've written for Scala 2.10/2.11 still compiles with 2.13. I think the biggest change for me was the redesigned collections-library, but that was rather simple migration. That said; there are a few breaking changes with the migration to 3.0 - especially if you rely on unsupported features of the compiler, namely macros. Macros have been widely used in the past and will not be supported anymore.