Free forecast vs cycled model runs
Cool, didn't realize that the GFS was on Github.
Looking on down the wiki, it seems like the &quot;free-forecast&quot; is associated with the deterministic model, while the &quot;cycled&quot; is associated with the Ensemble Kalman Filter. That is, the free-forecast is not constrained by data assimilation algorithms- it can just start from a restart file and go. A cycled run, however, needs multiple runs, as well as data.
This is all speculation based on naming conventions. If you really want an answer, perhaps asking the code developer?