Model Releases
@WeAreDevs Here's how I define 'Fable class models' - first Claude Fable 5, now Claude Opus 5.5 and GPT-Astra 6 and maybe GPT-5.6 Sol as wel…
Simon Willison defines “Fable class models” as a lineage of generative AI systems that began with Claude Fable 5, progressed to Claude Opus 5.5, and later included GPT‑Astra 6 (with a possible additio
Simon Willison defines “Fable class models” as a lineage of generative AI systems that began with Claude Fable 5, progressed to Claude Opus 5.5, and later included GPT‑Astra 6 (with a possible additional variant GPT‑5.6 Sol). His description was posted on Twitter on 28 September 2026 and has garnered approximately 2,927 views.
Related
- Here are Fable's pelicans for the different thinking effort levels, plus how much each one cost to generate via the Claude API
- A TIL on using http://agentsview.io to calculate token spending with Claude Fable 5 despite that model not yet being included in the AgentsV…
- ... four years later, I got the new Claude Fable 5 to actually build the game https://x.com/simonw/status/2085089518223602058
- Wrote up my initial impressions of Claude Fable 5 - it has a big model smell: slow, expensive and capable of crunching through pretty much e…
Source: Simon Willison (X) | 2026-09-28