I wrote a Python-API for OGS5 as presented at the user-meeting on 2019-01-11.
You can find it on Github as part of the GeoStat-Framework:
I also wrote a script-generation routine, to convert existing models to an ogs5py-script.
I created a repository where I converted most of the Benchmark-scripts (about 300). You can find it here:
A presentation and short introduction to ogs5py can be found here:
Presentation User-Meeting (Jan 2019)
Feel free to contribute and I would be happy about any suggestions!