It’s implied that they do, but don’t have the balls to tell you they do.

They tell you, and allow you to opt out in certain plans.

Except when their automated reviews decides that you've written something dangerous, in which case they'll use it for training.

And no, they won't tell you what their automated reviews consider "dangerous".

And neither will they make clear what "analytical purposes" is for the data you can't opt out of.

So they give you the ability to "opt-out" of "training purposes", and then you still share everything for analytical purposes (which you can't opt out of). It's a smart tactic on their side if they are contributing to cultural discourse on this to keep the straw man focus on training data.

And also to have the popular AI straw man: that your data isn't valuable and oh man they're losing so much money on tokens and giving you a subsidy, so you you better use up your entire subscription balance weekly/daily/every 5h putting in all your "worthless" data that you miss out otherwise (FOMO). Oh man only way it could get worse is if they implemented gambling slots psychology.