I spend a lot of time telling Opus 4.8 to search for security bugs in the code it wrote, and it spends a lot of time finding them, and then fixing them. Fable wont let me fix the security issues that Opus 4.8 created.
Not the OP but my Fable says something to the effect of "I'm afraid I can't do that Dave" and very obviously (not secretly) downgrades to Opus. I work in life sciences.