When OpenAI announced on 7 October that GPT-6 was coming to everyone, it was true, with a catch. There are two versions. Paid plans (Plus, Pro, Business and Enterprise) use GPT-6 Sol. The Free plan and the cheaper Go plan use GPT-6 Luna. Same family, same headline, quite a different experience once you push it.

If you're on Free or Go and wondering whether you're missing out, here's what actually differs, and how to tell whether it matters for the way you use ChatGPT.

Which plan gets which model

• Free: GPT-6 Luna, with ads.

• Go ($8 a month in the US): GPT-6 Luna with more room than Free. It may also include ads.

• Plus ($20 a month in the US): GPT-6 Sol, no ads.

• Pro 100, 200 and 500: GPT-6 Sol plus the Pro model, GPT-6 Astra. We broke down the three Pro plans in ChatGPT Pro 100 vs 200 vs 500.

One small warning if you go digging: some of OpenAI's help pages still call the free model GPT-5.6 Luna. The launch announcement and the pricing page say GPT-6 Luna. The help pages appear to be catching up.

What actually differs

How hard it can think. This is the biggest difference. On Free and Go you get the quick Instant mode and a Think button for harder questions. Plus adds the Medium and High thinking levels, and Pro goes up to Extra High. For a quick email, a caption or a recipe you won't notice. For a messy problem, such as working through a contract, planning a launch or checking the logic of a spreadsheet, the deeper levels are where Sol pulls ahead.

How much it can hold at once. This is the context window: roughly, how much of your conversation and files it can keep in mind. According to OpenAI's pricing page, Free gets 27K in Instant mode, while Go and Plus get 54K, rising to 256K when thinking. Pro gets more again. If you paste in a long document and it starts forgetting the beginning, this is usually why.

Speed. Free and Go are described as limited on bandwidth and availability, which in practice means slower answers at busy times. Plus is listed as fast.

The extras. Deep research and Codex are limited on Free and Go and expanded on Plus. Memory is limited on Free, longer on Go and expanded on Plus. Scheduled tasks come with Go and Plus but not Free. ChatGPT Work is desktop only on Free and Go, and also on web and mobile with Plus.

What about limits?

This is where it gets vague. OpenAI says everyday text chats aren't capped on any plan, subject to guardrails against abuse. The limits sit on the heavier things: uploads, image generation, voice, data analysis and the thinking modes. OpenAI doesn't publish the numbers for Free or Go, only that Go gets more than Free, apart from voice, which is the same.

When you hit a thinking limit, ChatGPT shows when it resets and may carry on with a lighter model in the meantime.

So you can't plan around a number. You can plan around a pattern: if you keep seeing reset messages on the days you actually need it, that's your answer.

And the ads

Ads appear on Free and Go only, and have been live in the UK since June 2026. Go's pricing card says the plan "may include ads", so paying $8 doesn't buy you an ad-free ChatGPT. Plus does. If ads in the middle of a work conversation bother you, that alone may settle it.

How to decide in a week

Don't decide from a comparison table. Decide from your own use. For one ordinary week, whenever ChatGPT frustrates you, note which of three things happened: it ran out (a limit), it gave a shallow answer that more thinking would have fixed (the model), or it forgot something you'd told it earlier (the context window).

• If it's mostly nothing, stay on Free.

• If it's mostly limits on uploads or images, Go is the cheap fix.

• If it's mostly shallow answers to hard questions, or forgetting long documents, that's the gap between Luna and Sol, and Plus is the step that closes it. We look at that decision properly in Is ChatGPT Plus Still Worth It in 2026?

Whichever model you're on, the quickest improvement costs nothing: stop starting from scratch. A model that already knows your job, your priorities and how you like answers back does more with every message, which matters most on the plans where the heavy features are rationed. That's what AI for Creators sets up, in ChatGPT or Claude.

US list prices as of 12 October 2026. UK prices include VAT and are shown at checkout. OpenAI's help pages are still being updated after the GPT-6 launch.