Each of those history items was selectable, and you could continue any of those conversations.
To do that, they need to store the model state (to allow continuation).
But when they switch out the model, the old model states wouldn't be valid anymore - they need regenerating.
Regenerating the model state for a new model uses as much computation as the original conversation did.
So, if they want to restore history, they have to do all the compute work they have done in the past, again. Thats gonna be a lot of GPU-hours - Expensive!
Another option is they set up another smaller farm of the old model version, and use that for continuing old conversations - but obviously thats some effort to set up, and they'd need to dedicate a set of a few hundred GPU's to running each old version forever. - Expensive!
Or yet another option is they show old conversations, but don't allow continuation. That probably just requires a little dev work - and in their position, thats what I'd do. - Worse user experience.
To do that, they need to store the model state (to allow continuation).
But when they switch out the model, the old model states wouldn't be valid anymore - they need regenerating.
Regenerating the model state for a new model uses as much computation as the original conversation did.
So, if they want to restore history, they have to do all the compute work they have done in the past, again. Thats gonna be a lot of GPU-hours - Expensive!
Another option is they set up another smaller farm of the old model version, and use that for continuing old conversations - but obviously thats some effort to set up, and they'd need to dedicate a set of a few hundred GPU's to running each old version forever. - Expensive!
Or yet another option is they show old conversations, but don't allow continuation. That probably just requires a little dev work - and in their position, thats what I'd do. - Worse user experience.