There is now a working changelog/diff function for the API docs. It's at
It's not perfect, but should hopefully be helpful.
I've also changed the URL for the API docs; it's now at https://groups.io/api
The /createsubgroup endpoint is now working and the docs have been updated with the correct parameters.
I noticed today that I'm a bit inconsistent in using "bad_request" versus "invalid_value" in errors. My gut says to get rid of one of them. I will figure that out early next week.
Please let me know if you see anything or have suggestions.