>and why price it day 1 at 1/2 the cost of Fable?

Why would they price it the same as Fable it it doesn't cost the same as Fable ?

That's half my point - Anthropic's remarks suggest that is Fable significantly bigger (hence more costly to run) than Opus, so it is priced accordingly, but GPT 5.6 priced the same as 5.5 is one datapoint that suggests they are the same size.