xflr5 v6 legacy project files (.xfl) can be imported into flow5.
The XML format of plane and polar objects has been slightly modified to conform to the new data structures, which means that legacy files will not be usable in flow5.
The format of the foil polar files (.plr) is unchanged, so legacy .plr files can be read by flow5.
Note that airfoil and polar data can be exported from flow5 in the legacy .xfl format, so that the exchange of airfoil polar data between the two applications is seamless.
Lastly, there is no backward compatibility, i.e. project files generated by flow5 (.fl5) are not readable by xflr5.