The GPT-6 Family Tree: Astra, Sol, Terra and Luna

OpenAI released GPT-6 Astra on Sep 3, 2026, and says it is "state-of-the-art on computer use, browsing, software engineering, cybersecurity, science, and professional work". Its standard API price is $10 per million input tokens and $50 per million output tokens. Over the next eight weeks OpenAI released four more GPT-6 models, each priced below Astra: GPT-6 Sol and GPT-6 Luna on Sep 22, GPT-6.1 Sol on Sep 29 and GPT-6.1 Terra on Oct 26.

Each model is trained like Astra

OpenAI's system cards describe each later model by Astra's training. An appendix added on Sep 22 to the Astra system card says "GPT-6 Sol and Luna use the same types of data and training as GPT-6 Astra", and the system card addenda for GPT-6.1 Sol and GPT-6.1 Terra say the same of each. The Sol and Luna post adds that OpenAI "trained GPT‑6 Sol and Luna with similar methods as GPT‑6 Astra". None of these pages calls a model distilled from Astra.

Each also follows an earlier model

OpenAI's posts also tie each new model to one before it. The Sol and Luna post prices them in a table that runs from GPT-5.6 Sol to GPT-6 Sol and from GPT-5.6 Luna to GPT-6 Luna, and says Luna "improves on its predecessor". Later posts call GPT-6.1 Sol "an upgrade to GPT-6 Sol" and GPT-6.1 Terra "a significant step up from GPT‑5.6 Terra". The three GPT-5.6 models reached general availability together on Jul 9. The Astra post compares Astra with GPT-5.6 Sol, which it calls "our previous frontier cyber-capable model".

Prices fall from $10 to $0.10 per million input tokens

At launch, GPT-6 Sol and GPT-6.1 Sol cost $2 per million input tokens and $10 per million output, a fifth of Astra's prices. GPT-6.1 Sol cut cached input to $0.10, half of GPT-6 Sol's. GPT-6.1 Terra costs $1 and $5, and GPT-6 Luna $0.10 and $0.50, a hundredth of Astra's.

Which ChatGPT plans get each model

The Astra launch post says Astra rolled out first to a limited set of organizations and would become available to all ChatGPT Plus, Pro, Business and Enterprise users over the coming days, with Enterprise access off by default at launch, and that Pro, Business and Enterprise users also get GPT-6 Astra Pro. OpenAI's help center lists GPT-6 Pro, "powered by GPT‑6 Astra", for Pro $100, Pro $200, Business and Enterprise, and says Plus includes Astra in ChatGPT Work and Codex.

GPT-6 Sol and GPT-6 Luna came to ChatGPT Work and Codex for Plus, Pro, Business, Enterprise and Edu users, and Free and Go users got GPT-6 Luna in the desktop app. GPT-6.1 Sol followed for the same plans, rolling out to Pro users first, the release notes say. GPT-6.1 Terra's post lists Plus, Pro, Enterprise and Edu, and the release notes add Business.

On Oct 7, OpenAI brought GPT-6 to ChatGPT's Chat tab, calling it "a new GPT‑6 model". The post and the release notes say it is powered by GPT-6 Sol for Plus, Pro, Business and Enterprise and by GPT-6 Luna for Free and Go, with the Free and Go rollout to start the next day. The post adds that both are "tuned for everyday conversation".

Faster tiers

In the API, Astra's Fast mode "delivers up to 2x the speed of Standard processing at 2x the Standard price", the launch post says. On Sep 29, OpenAI's API changelog added Ultrafast mode for GPT-6 Astra in the Responses API, "to reduce the time between generated output tokens". OpenAI's pricing page lists Astra Ultrafast at $60 per million input tokens and $300 per million output. On Oct 8, the changelog added Ultrafast for GPT-6.1 Sol, which the pricing page lists at $12 per million input tokens and $60 per million output.

GPT-6 Rosalind for life sciences

OpenAI's API changelog lists GPT-6 Rosalind on Oct 30, for organizations "approved for Rosalind Research through the trusted-access program", and the pricing page lists it at $15 per million input tokens and $75 per million output.