Well, practically speaking it is banned to some extent. Some individual thinks they are clever and posts a reply that clearly is generated by ChatGPT and gets suspended for posting nonsense. There's no 'formal' rule because don't post crap is obvious.
I think there's an important point to be made that meta supports the network as a whole, and as such, well posts need to show understanding of the question, context and sometimes history of the network.
So far, a good chunk of ChatGPT posts we've run into fall into 3 broad categories - they tend to be new users with no apparent activity elsewhere, folks answering the question on how to detect ChatGPT or spammers. It’s also invariably 'new' users or at least throwaway accounts.
And frankly I've not seen any actual 'considerate' use of the tool, nor any real awareness of the network in these posts.
Fundamentally, the way it shows a certain lack of effort, respect for the commons, is essentially plagiarism and frankly is folks trying their luck.
When we do suspensions - here's a strange thing, the users rarely respond. I got an apology on Pets where I warned someone. Here? I can suspend someone a year and... no reply. It’s almost like they don't care, or want to find out if they can get away with it.
With nearly all these being 'new' users, I also feel like there's no good intent being demonstrated here.
Let’s say, hypothetically - someone trained a ChatGPT type tool on - well meta. Maybe the collected works of Shog9. It answers questions perfectly with awareness of the actual question and doesn't give generic prepackaged dog chow. I'd certainly be impressed - and consider it useful. So far that has not been the case.
On the other hand, the poor quality, lack of effort and the noise these posts create mean they don't add value and should be discouraged.
Basically, I'd say 'don't try your luck' if you want to do it, and we reserve the right to deal with folks trying their luck as we deem appropriate.