OpenAI launched GPT-6.1 Sol on September 29, 2026 at DevDay, included on paid ChatGPT plans and the API the same day. Reported API pricing is $2 input, $10 output, and $0.10 cached input per million tokens — the same $2/$10 list as GPT-6 Sol (September 22), with 6.1 as the capability upgrade. OpenAI positions it against GPT-6 Astra at $10/$50 standard. Tibo called it a good, unusually efficient model; OpenAI called it the most cost-efficient model for its performance available that day.