OpenAI's New GPT-6 Sol and Luna Models Bring Astra Improvements to Cheaper Tiers

Tuesday September 22, 2026 1:58 pm PDT by Juli Clover

OpenAI today launched GPT–6 Sol and GPT–6 Luna, two new models that follow GPT–6 Astra. OpenAI says the new models were developed using methods similar to Astra's for improvements in professional work, factuality, coding, computer use, and alignment.

GPT–6 Sol is for everyday work, and it costs less than Astra. GPT–6 Luna is an even cheaper model. Luna is optimized for fast responses and higher volume, while Sol has more reasoning capability.

The new models outperform their predecessors on OpenAI's benchmark tests, and GPT–6 Sol makes "about half as many mistakes" as GPT–5.6 Sol. GPT–6 Sol shows improvements in coding and computer use compared to GPT–5.6 Sol, and it matches or beats Claude Fable 5.1 scores on some benchmarks.

OpenAI compared GPT–6 Sol to Opus 5 on several tests, but Anthropic released a new Opus 5.5 model today that outperforms Astra on some coding and knowledge work benchmarks.

GPT–6 Sol and Luna are adopting the improved communication style OpenAI introduced with Astra for simplified conversations with less jargon and fewer low-value details. Answers should be slightly shorter without losing substance, and the new models have lower rates of misleading claims about their coding work in OpenAI's alignment testing.

OpenAI is lowering token prices for Sol and Luna compared to their 5.6 counterparts, and prompt caching has been improved. OpenAI says agents will reuse more context, respond faster, and get 90 percent discounts on cached input-token reads.

GPT–6 Sol is priced at $2 per million input tokens and $10 per million output tokens, down by half. GPT–6 Luna costs $0.10 per million input tokens and $0.50 per million output tokens, down from $0.20 and $1.20, respectively. GPT–6 Sol costs half as much per token as Opus 5.5, but Anthropic says Opus 5.5 uses fewer tokens per task than Opus 5, so it's not a straight comparison.

GPT–6 Sol and GPT–6 Luna are rolling out in ChatGPT Work and Codex starting today for Plus, Pro, Business, Enterprise, and Edu users. GPT–6 Luna is available to Free and Go users in the desktop app. GPT–6 Sol and Luna are not yet available in Chat mode.

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