The US government basically told them they can't sell "Fable" and so they aren't. That's probably 90% of the story. Once the government stepped in, their 5th generation was effectively killed. They either had to lock it up (Mythos), neuter it (Fable), or leave people with the perception they were overpaying for a weaker model (Opus 5). Hopefully Anthropic has learned to anticipate this risk and has a plan for rollout…
The government seems like it's in a rough spot. If they let Mythos out, they seem worried people could use it to mass-hack the internet. China seems to not care so much about this and they're right behind. I don't really know what the answer is.
(Or perhaps vulns that NSA/etc discovered and has been keeping it private; as they're known to do).
I feel there's a lot that's unaccounted for, and the whole "AWS team reports a 'jailbreak' that is just 'review this codebase'" story doesn't add up.
I wonder if there were some parallel construction going on, and if at the same time, the NSA started losing the exploits they had because it was getting patched.