It's currently about as fast as Scala 2.12, which means it compiles at roughly 3000 lines/sec. However, it supports more aggressive incremental compilation than Scala 2 so at least in my projects, which are typically 50K to 100K lines, most compiles are under a second, and I rarely see compile times over 5 seconds.

There's ongoing performance work to make both Scala 2 and Scala 3 faster than they are now. A lot of what people perceive as slow compile times are actually other factors (such as inefficient macros or slow build tools).