Claude Fable 5.1 & GPT-6 Astra packages are live

spec-driven

AI

Spec-driven development for agents — propose, spec, tasks, verify, archive before any multi-file edit, so the model builds what was agreed and leaves…

Choose your model

Available for 11 model families. The engineering substance is the same in each; the structure, checklist phrasing and constraint ordering are tuned per family.