A modern programming language that makes developers happier.

kotlinlang

According to <https://docs.spring.io/spring-boot/3.5/appendix/dependency-versions/coordinates.html|the dependency documentation>, the upcoming Spring Boot 3.5 will still be on Kotlin 1.9.x.
Is there any information about why they do not upgrade to 2.x?

Most likely because there's no particular reason to do so. That doesn't prevent you from using Kotlin 2 in your project.

It's because Spring Boot 3.5 is still based on Spring Framework 6.2.x, <https://docs.spring.io/spring-framework/reference/6.2/languages/kotlin/requirements.html|which has Kotlin 1.7+ as its baseline>.
Spring Boot 4.0 will be based on Spring Framework 7 – <https://docs.spring.io/spring-framework/reference/7.0/languages/kotlin/requirements.html|which (currently) has Kotlin 2.1+ as its baseline>.

We are using Spring Boot 3.4.x and the latest Kotlin 2.1.x, worked well.

To use RabbitMQ/AMQP in Spring Boot, just configure it in properties and declare a Jackson base message converter.