Q: When running my GAMS model, other directories are created as well. These directories are named 225a, 225b, 225c, etc. and contain several files. My question is, do I need to keep these 225a (etc.) directories, or is it safe to delete them as they take up space?

These directories are only needed while your GAMS job is running.

If you have those directories still there you either used gamskeep instead of gams. Or your job crashed or it was interrupted by a hard kill (e.g. Ctrl-Break on Windows). If this happens, the GAMS job will be terminated immediately and no cleanup occurs.

In all cases you can delete these 225? directories safely. Within the GAMS IDE you may use the menu Utilities → Delete 225 directories to delete these sub directories of the current project directory.