OpenAI Releases GPT-6 Sol and Luna, Pricing Sol at Half of Claude Opus 5.5

OpenAI released GPT-6 Sol and GPT-6 Luna on September 22, 2026, adding lower-cost GPT-6 options beneath GPT-6 Astra for developers using its APIs. The pricing makes Sol a direct challenge to Anthropic's new Claude Opus 5.5: OpenAI lists Sol at $2 per million input tokens and $10 per million output tokens, exactly half of Opus 5.5's $4 and $20 rates.