All ExtendSim versions are upwardly compatible. So ExtendSim 2024 will read in models built in ExtendSim 10, 9, 8, and 7. ExtendSim 10 will read in models built in ExtendSim 9, 8, 7, and Extend 6. And so on.
However, ExtendSim is not backwardly compatible. Models and blocks you build in ExtendSim 2024 cannot be read by earlier versions, such as ExtendSim 10 or ExtendSim 9.