All ExtendSim versions are upwardly compatible. So ExtendSim 10 will read in models built in ExtendSim 9, 8, and 7. ExtendSim 9 will read in models built in ExtendSim 8, 7, and Extend 6. And so on.

However, ExtendSim is not backwardly compatible. Models and blocks you build in ExtendSim 10 cannot be read by earlier versions, such as ExtendSim 9 or ExtendSim 8. Models and blocks you build in ExtendSim 9 cannot be read by earlier versions, such as ExtendSim 8 or ExtendSim 7.