Fable 5 – Median thinking declined in August

Lon Lundgren on X: "After Anthropic made Fable 5 permanently available in subscription plans, I noticed a large drop in performance. The model felt dumber, and I couldn't explain why.

Measured five different ways, August delivered dramatically fewer thinking tokens than July." / X

Measured five different ways, August delivered dramatically fewer thinking tokens than July."

After Anthropic made Fable 5 permanently available in subscription plans, I noticed a large drop in performance. The model felt dumber, and I couldn't explain why.

Measured five different ways, August delivered dramatically fewer thinking tokens than July.

This wasn't a one-time drop. Reasoning fell over the entire period, and fluctuated across multi-day episodes.

Some of these fluctuations aligned with specific product announcements and releases.

I started to see how the model could feel great one day, and terrible the next.