Are project files made in StreamAuthor 1.x or 2.x compatible with StreamAuthor 3.x?

Yes, but we would suggest users to convert StreamAuthor 1.x and 2.x project files prior to opening them in StreamAuthor 3.0. When you open an older project, a warning message will popup to ask you "Do you want to convert it to StreamAuthor version 3.0 format?"
Just click "Yes" to continue processing and generate a compatible version.

Strongly suggest that you backup the original project files created by StreamAuthor 1.x or 2.x before convert into 3.x project.