Context:

• Dario “Pacing the Frontier”

• Sonnet 3.5 - 4.5 were all Anthropics “frontier model” at time of release (June ‘24 - Sep ‘25)

• since Opus 4.5 - 5.5 (Nov ‘25 - Sep ‘26), only Opus and Mythos/Fable were released as “frontier models”

Resolves based on Anthropic System card / marketing for new (public) model releases

e.g. Sonnet 5.5 would have been NO based on the system card (167.93 < 169.12)