OpenAI halves API prices with GPT-6 Sol and Luna

OpenAI released GPT-6 Sol and GPT-6 Luna on 22 September 2026, about an hour after Anthropic announced Claude Opus 5.5. GPT-6 Luna costs $0.10 per million input tokens and $0.50 per million output tokens, down from $0.20 and $1.20 for its predecessor GPT-5.6 Luna. GPT-6 Sol costs $2 and $10, against $4 and $20 for GPT-5.6 Sol. The comparison comes from Simon Willison, who put the new models side by side on the day of release.

Anthropic is cutting prices with Opus 5.5 as well. Opus 4.5 through Opus 5 cost $5 for input and $25 for output per million tokens; Opus 5.5 costs $4 and $20, and cache reads are 60 percent cheaper. Opus 5.5 has a maximum output of 128,000 tokens. According to Willison, GPT-5.6 is scheduled for a 25 percent price increase in November.

Why it matters: Anyone running high-volume classification or extraction pays less than half the previous output price with GPT-6 Luna. The announced increase makes staying on GPT-5.6 more expensive from November, so existing pipelines built on language models should be tested against the new generation before then. Willison's comparison covers pricing; by his own account, a solid read on the quality of Sol and Luna is still to come.