Openfire Backwards Compatibility with Spark

I have an Openfire sever currently running at version 3.7.1 and looking to update to version 4.1.3.

Most of our users run Spark version 2.6.3 on their PC’s. What is the backwards compatibility like when upgrading the Openfire Server?

When Openfire 3.10.0 was released Spark 2.6.3 stopped working properly with it (couldn’t login with SSL), so 2.7.0 has been quickly released. Though i’m currently able to login with 2.6.3 to 4.1.3 server and it seems to work (although it takes very long to login). But i advise to at lease go to 2.7.7 version.