GPT-6 models explained: Astra vs Sol vs Luna vs Terra

OpenAI replaced its whole line-up in September and October 2026 with the GPT-6 family, and gave the models space-themed names instead of numbers. If you’re confused, you’re not alone. Here’s the plain-English version.

Quick answer: Astra is the most powerful, Sol is the everyday workhorse, Luna is the cheap and fast one, and Terra is the new low-cost model for operating computers. In ChatGPT you mostly don’t choose: your plan decides.

The four GPT-6 models

Model	Released	What it’s for	API price (in / out, per 1M tokens)	Context
GPT-6 Astra	Sep 3, 2026	Hardest reasoning, long research, complex coding	$10 / $50	~1.05M tokens
GPT-6.1 Sol	Sep 29, 2026	Everyday work, the sensible default	$2 / $10	~1.05M tokens
GPT-6 Luna	Sep 22, 2026	High-volume, simple tasks	$0.10 / $0.50	~1.05M tokens
GPT-6.1 Terra	Oct 26, 2026	Computer use, reading screens, fast writing	$1 / $5	Check OpenAI

From OpenAI’s API changelog and announcements. A million tokens is roughly 750,000 words.

Astra: the heavyweight

GPT-6 Astra is the most capable and most expensive GPT-6 model, at five times the API price of Sol. In ChatGPT, it powers Pro reasoning on the Pro plan (from $100 a month). Use it for problems where getting the answer right is worth a lot: long research, tricky analysis, multi-step coding.

Sol: the everyday default

GPT-6 Sol arrived on September 22, 2026, and GPT-6.1 Sol replaced it a week later. It’s the middle tier and the sensible default for most apps built on OpenAI: strong enough for most tasks at a fifth of Astra’s price.

Luna: cheap and fast

GPT-6 Luna costs 10 cents per million input tokens. It’s built for jobs that run thousands of times, like tagging support tickets or summarizing short messages, where speed and cost matter more than depth.

Terra: the computer-use specialist

GPT-6.1 Terra is the newest, released October 26, 2026. OpenAI describes it as fast and efficient, with strong visual reasoning and precise computer use: it can look at a screen and click, type and navigate apps for you. It costs half the API price of GPT-6.1 Sol. In ChatGPT it’s available to Plus, Pro, Enterprise and Edu users in ChatGPT Work and Codex, not the regular chat.

Which one do you need?

• Using ChatGPT: you don’t pick a model directly. Free gives unlimited GPT-6 chats, Plus adds advanced reasoning, and Pro adds Astra. See ChatGPT Go vs Plus vs Pro.
• Building with the API: start with Sol. Drop to Luna for simple, high-volume jobs, use Terra for agents that operate screens, and save Astra for the hardest problems.

How they compare with Claude and Gemini

Anthropic and Google refreshed their models the same autumn. GPT-6.1 Sol’s $2 / $10 API price matches Claude Sonnet 5.5 and Gemini 4 Argon’s introductory price. See our new models tracker for every release, or read Claude Fable vs Opus vs Sonnet for Anthropic’s line-up.