The set up doesn’t seem like the classic scenario since there’s a way out. It’s more Kobashi Maru.
pre-crime promise - if caught, don’t rat
Scenario:
Both confess - each 6 years
You confess, anon no rat - you free, anon get 4
Anon confess, you no rat - anon free, you 4
Both no rat - 2 years
As rational and self-interested, you both confess (in hopes of getting no time), and knowing you can’t trust other to keep pre-crime promise (since they also rational and self-interested)
As a result, you both get 4
Why not rat in such a scenario?