Looking at the "Update a group" page we deduced the URL to GET a named group, but that didn't return the properties. Further looking at Get all contact properties by groupName it shows we can include the includeProperties=true parameter as well.
Could you please update the documentation to show this?
Also - is there an email list or similar where we can sign up to get changes to the API, or upcoming deprecations?
The 'Get Contact Property Groups from a Portal' endpoint has been deprecated since December 2014. Upcoming/new API changes will be announced on the forums; subscribing to the 'Announcements' topic is one of the best ways to keep updated with API changes. For HubSpot product updates, you can also check out the product updates blog (see below).
Regarding the other topic you linked to; that example is still valid, despite the fact that it's not documented. Consider that officially supported; I'll work on getting the Contact Properties API docs updated today.
Getting a Contact Property Group's properties isn't documented
Yes - thanks for that. Good to know there's a place for these announcements now, we'd asked in the past but were told there wasn't a way to get notified of changes.
Getting a Contact Property Group's properties isn't documented
I'd like to add that this is not the first time that an API has changed without us getting notified, thereby breaking our integration. This really is no way to run a public API. Please consider publishing an email notifying (paying) customers of upcoming changes, just like any self-respecting business would. (This is also not the first time we make this request.)