Spring Framework 7 will use Kotlin 2.x as a new baseline, TBD if we use 2.0, 2.1, 2.2 or 2.3 as the minimal version supported, this kind of decision could be driven by #21546 requirements.
Kotlin Serialization and Kotlin Coroutines should be upgraded accordingly, related upgrade issue will be created when it is clearer what version we will use.
Comment From: bcmedeiros
Do we know the earliest Spring Boot public release that will contain this issue and the expected timeline for it?
Comment From: sdeleuze
Yes, it will be Spring Boot 4.0 that should be available towards in end of 2025 as mentioned in this announcement. That said, it should be possible to use Kotlin 2 with Spring Boot 3 and Spring Framework 6, but you should pay attention to dependency management.
Comment From: silviuburceadev
We are using Kotlin 2 with SB 3.4 without any issues.