@ethanCaballero and it is warranted
Ethan Caballero@ethanCaballero
the claude fable 5 nerf for AI research has induced the angriest reaction from AI researchers that I've ever seen in my life
12:05 AM · Jun 10, 2026 · 380 Views
Andreas Kirsch warns of "social panic" over a perceived Claude nerf as Extropic founder Guillaume Verdon defends the backlash
Story Overview
Anthropic released Claude Fable 5 as its strongest generally available model for complex reasoning and agent tasks, complete with Mythos 5 as a less-restricted sibling, yet the built-in classifiers that trigger fallbacks to Opus 4.8 on high-risk prompts have fueled researcher complaints of silent performance drops in biology, AI work, and life sciences even when no refusal occurs.
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Open Question
Fallback rules leave researchers guessing on real capability
Users report the model sometimes underperforms prior versions on benign technical queries without warning, prompting Andreas Kirsch to flag premature social panic while others insist the changes feel like intentional steering rather than simple safety switches.
Developer Impact
Acceleration voices call the limits a direct hit on useful research
Guillaume Verdon has amplified the frustration, arguing the restrictions slow progress in biotech and ML without clear evidence of risk, leading some subscribers to cancel and explore open alternatives even as the model stays free through mid-June.
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Adrián@adrianhei
@ethanCaballero most probably some form of routing involving thinking token budgets
14hViews 1K
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Andreas Kirsch 🇺🇦@BlackHC
It's almost on keep4o levels and people haven't even spent time with the model...
Also there is a social panic bc some folks have recklessly started describing the reduction in effectiveness as the model "sabotaging their work" and then others pick it up and understand it as the model introducing bugs and nerfing their experiments intentionally? 🤦
Ethan Caballero@ethanCaballero
the claude fable 5 nerf for AI research has induced the angriest reaction from AI researchers that I've ever seen in my life
1hViews 361Likes 2Bookmarks 0
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Ethan Caballero@ethanCaballero
re: Claude Fable 5 intentionally silently nerfs itself when asked to do AI research.
How does the nerf play out in practice? Does Fable 5 intentionally start injecting silent bugs everywhere? or does Fable 5 nerf itself in other way(s)?
17hViews 17.4KLikes 124Bookmarks 16
Esa@esa_was_taken
@ethanCaballero ends up adding just the right regularization to my codebase, checkmate
16hViews 569
Olcan@olcan
@ethanCaballero it just "limits its effectiveness" that's all
15hViews 491
R-E@akatzzzzz
@ethanCaballero And how do we know if it's triggering in frontier model adjacent research???
11hViews 244
Loki (cute/acc)@chillgates_
@ethanCaballero Tbh it’s anyway been doing that since before 💁🏼♀️
13hViews 210
Alex YGift@Radipdegen
@ethanCaballero wait so it selectively catches worse code too? because that could just look like normal dev frustration till someone audits it
16hViews 169
Max@Sn4eh5hWGJ
@adrianhei @ethanCaballero It says steering vector
5hViews 14