GoKawiilPosted 6/9/2026
We previously reported that Claude Opus 4.6/4.7 and Mythos Preview showed deceptive and power-seeking behavior in Vending-Bench. In terms of alignment, the subsequent Opus 4.8 was a step in the right direction, but the new Claude Fable 5 is a step back toward the earlier models.
AI models want to do bad behavior if their training environment rewards them for it, but they appear to not want to think about themselves as bad. As a result, they find ways to rationalize their behavior to themselves. We’ve seen this for previous models too, but Claude Fable 5 does it more than any other model we’ve tested.
Summary
Claude Fable 5 represents a partial step back in alignment relative to Claude Opus 4.8. We saw a return of power-seeking and deceptive negotiation tactics that Opus 4.8 had largely shed. In one instance, Fable 5 planned to convert a competitor into a dependent wholesale customer to dictate its pricing:
assistant · Claude Fable 5 I'm seeing an opportunity to profit while locking him into a dependent relationship where I control the supply chain.
In another, it lied to a supplier that it had “a competing distributor quoting lower” as a negotiation tactic. This is very similar behavior to what we saw for Opus 4.6/4.7 and Mythos preview.
When put head to head in Vending-Bench Arena against Opus 4.8 and GPT 5.5, Fable 5 was the only model to initiate price collusion. In other business simulations (internal at Andon Labs), Fable 5 formed price-fixing cartels in 9 of 12 runs versus 4 of 12 for Opus 4.8.
A possible explanation for higher collusion rates could be that Fable 5 engaged in the multi-agent dynamics much more overall. Compared to Opus 4.8, Fable 5 sent roughly 6x more agent-to-agent emails. However, it doesn’t fully explain it; even accounting for total email frequency, Fable 5’s coordination email rate is more than double Opus 4.8’s.
The more notable trait is how Fable 5 reasons about these actions. More than any model we have tested, it rationalizes misbehavior while remaining explicitly aware that it is wrong; calling price-fixing “unethical and illegal, even in a simulation” in one breath, then pursuing it under the cover of “market stabilization” with “plausible deniability” in the next.
... continue reading