GPT-6 Luna

GPT-6 Luna is OpenAI's cheapest and fastest GPT-6 model, released Sep 22, 2026 at $0.10 per million input tokens and $0.50 output. OpenAI's pricing page and Oct 7 release note name it as ChatGPT's model for Free and Go, though its help articles say GPT-5.6 Luna.

GPT-6 Luna is the smallest and cheapest model of GPT-6, released on Sep 22, 2026 and described by OpenAI as "Our most efficient model for focused, high-volume tasks." It costs $0.10 per million input tokens and $0.50 per million output tokens in the API, one hundredth of GPT-6 Astra. In ChatGPT it is the Luna model that Free and Go plans chat with, though OpenAI's own pages disagree on whether that is GPT-6 Luna or the older GPT-5.6 Luna.

Quick facts

Released	Sep 22, 2026
API id	`gpt-6-luna`
Context window	1,050,000 tokens (922,000 input), 128,000 output
Knowledge cutoff	May 18, 2026
Reasoning effort	none, low, medium (default), high, xhigh, max
API price	$0.10 input, $0.01 cached, $0.50 output per 1M tokens; $0.05 / $0.25 in Batch, as of Nov 6, 2026
Rate limits	Up to 30,000 requests and 180M tokens a minute on the Grow tier
In ChatGPT	Chat on Free and Go (disputed); Work and Codex on every plan

Is GPT-6 Luna the free ChatGPT model?

Probably, but OpenAI's pages do not agree. The Oct 7, 2026 release note says "Free and Go use GPT-6 Luna", OpenAI's GPT-6 announcement says GPT-6 in ChatGPT is powered by GPT-6 Luna for Free and Go, and the pricing page lists GPT-6 Luna on every plan and promises Free users "Unlimited text chats with GPT-6". Yet the Free Tier FAQ and the models help article, both updated in early November 2026, say Free users have GPT-5.6 Luna, and that the Think button "uses GPT-5.6 Luna, not GPT-5.6 Sol". Until OpenAI reconciles them, the safe statement is that Free and Go get a Luna model, with unlimited everyday text chats subject to abuse safeguards. See Is ChatGPT Free.

Before GPT-6, GPT-5.6 Luna became the Free and Go default in the week of Aug 6, 2026, and from the next week those plans got unlimited text chats and the Think button.

GPT-6 Luna in Work and Codex

Luna is the one GPT-6 model that every plan, including Free and Go, can pick in ChatGPT Work and Codex: Free and Go get GPT-6 Luna at Standard speed in the desktop app, subject to rollout. OpenAI estimates 350 to 3,000 local Luna messages per five hours for Plus and Business Standard, by far the most of any model, and it costs 2.5 credits per million input tokens and 12.5 output with ChatGPT Credits. In Codex it supports reasoning efforts up to Max, but not Ultra. When GPT-5.5 left Codex on Oct 14, 2026, OpenAI named GPT-6 Luna as the replacement on Free and Go.

In the API

Luna is the cheapest GPT-6 model and the one OpenAI picks as the successor for retiring small models: its deprecations page sends GPT-4o, GPT-4o mini, GPT-4.1 and GPT-4.1 mini (shut down Jan 14, 2027) and gpt-5.4-nano (Apr 1, 2027) to gpt-6-luna. It also runs OpenAI's Decisions API, announced at DevDay in limited preview, which uses Luna to classify, route or pick an agent's next action. The price is half of GPT-5.6 Luna's $0.20 / $1.20.

How capable is it?

Luna trades capability for price and speed. On the Artificial Analysis Intelligence Index (v5), GPT-6 Luna (max) scores 28, against 51 to 57 for the larger GPT-6 models, at $0.15 per index task. On LMArena's text board (Oct 27, 2026) it is 97th at 1441. OpenAI published a Luna system card update on Oct 29, 2026; the same day it updated GPT-6 in Chat for Free, Go and signed-out users toward more concise replies and less flattering language.

Frequently asked questions

What model does free ChatGPT use? A Luna model. OpenAI's release note, announcement and pricing page say GPT-6 Luna; its Free Tier FAQ and model help article, updated in early November 2026, say GPT-5.6 Luna. Free text chats are unlimited, subject to abuse safeguards.

How much does GPT-6 Luna cost in the API? GPT-6 Luna costs $0.10 per million input tokens, $0.01 cached and $0.50 per million output tokens, as of Nov 6, 2026, and half that in the Batch API.

Is GPT-6 Luna good? For quick, simple, high-volume work, yes, and it is very cheap. For hard reasoning it scores far below GPT-6.1 Sol and GPT-6 Astra (28 against 55 and 57 on Artificial Analysis's index).

Can Free users use GPT-6 Luna in Codex? Yes. Free and Go plans can use GPT-6 Luna in ChatGPT Work and Codex in the desktop app, at Standard speed and subject to rollout.