When I recently upgraded to the Assistant tier, one of the first things I did - before ever using the Assistant - was go into the settings and remove the default 24-hour duration of threads.
Every thread I've ever created has been permanent.
Despite that, the UI offers to allow me to 'preserve' each thread, which appears to be superfluous functionality;
I would even argue that the option only being provided for ephemeral threads could help alert users who may have accidentally created a temporary thread to the situation - whereas it always being shown regardless of whether it makes sense in context desensitises users to its presence.
