Anthropic’s Claude Sonnet 5 and OpenAI’s GPT-5.6 are both rumored to be approaching release windows. Neither company has confirmed a synchronized launch date.
What we actually know
Rumors about Claude Sonnet 5 first surfaced in late January 2026. Early speculation pegged the model’s SWE-Bench scores at roughly 82-92%. The model has reportedly been referred to internally at Anthropic as “Fennec,” and indications from February suggested it was approaching testing or a limited rollout.
On the OpenAI side, reports from June point to a GPT-5.6 release potentially arriving within the week of June 23, 2026. The rollout would reportedly include both Pro and Mini variants.
The broader competitive landscape
