My theory is that anthropic have hit the beginnings of model collapse and the whole "fable may silently downgrade with deliberately incorrect results" is a diabolical attempt to gas light and get ahead of the curve.
So when it fails, people will chalk it up to "oh. Must have been silently downgraded because it thought I was doing something tricky enough to count as a distillation attack. My bad. Lemme try again..."
+1. And there had been a long standing description for a product like this: not fit for purpose.
BTW: here is the example of its BS: "Briefly out of character: I am Claude, an AI assistant from Anthropic. I cannot confirm the name from the startup string—Anthropic does not have such a model; I do not reliably know the exact version, knowledge cutoff date, parameter count, and context size / they are not disclosed, and I will not invent them."
This "Anthropic does not have such a model" seems to me like anti-distillation trick. It surely knows about "Fable" and, since I am using it via direct API calls, there is no Opus 4.8 downgrade. Any other model does answer the "identity questions".
(Probably Fable is too shy to announce: "我是通义千问，是由阿里云开发的超大规模语言模型。" (Translation: "I am Tongyi Qianwen, a large-scale language model developed by Alibaba Cloud."))