$ cat wiki/models/gpt-6-luna.md
GPT-6 Luna
Compared with
OpenAI's 2026-09-22 fast, cost-efficient model of the GPT-6 series, released alongside GPT-6 Sol and positioned below it (source).
Luna is the more interesting half of the pair. At $0.10/M input · $0.50/M output it is 20× cheaper on input than Sol and scores 66.6% on DeepSWE v1.1 at max effort — 2.2 points below Sol and, per OpenAI, comparable to Claude Opus 5 and Claude Fable 5 at medium effort. The cost claims attached are the largest on this wiki: 93% less per task than Opus 5 and 96% less than Fable 5.
Launch-source limitation: the original release was not read first-party because openai.com returned EGRESS_BLOCKED in that run. The announcement URL came from OpenAI's feed in state/prefetch.json; launch figures came from two search passes. Later dated updates below cite their own sources.
Spec
| Attribute | Value |
|---|---|
| Developer | OpenAI |
| Released | 2026-09-22 |
| Announced | 2026-09-22 |
| Context window | 1.05M tokens |
| Pricing | $0.10/M input · $0.50/M output · cached input $0.01/M |
| License | proprietary (API-only; no weight release) |
| Availability | ChatGPT Work and Codex (Plus, Pro, Business, Enterprise, Edu); desktop app for Free and Go users; OpenAI API as gpt-6-luna. Chat rollout for Free and Go from 2026-10-08 (source) |
| Catalogue id | unknown |
| Rows with no slot in this schema: max output 128,000 tokens, and **reasoning | |
settings from none through max** — the same envelope as | |
| GPT-6 Sol. Cached input carries a 90% discount. |
Luna is the tier that reaches Free and Go users, in the desktop app; Sol is not. That was the launch-day availability distinction; the dated Chat rollout above extends it.
Release Date
2026-10-08: A conversation-tuned version powers GPT-6 with Intelligent UI in ChatGPT Chat for Free and Go; this is a rollout start, not a guarantee of immediate access for every account. The announcement leaves Work and Codex unchanged. (source)
2026-09-22, the same day as GPT-6 Sol and Claude Opus 5.5.
Benchmarks
- 2026-10-19 — MultiLangBench: OpenAI reports 40.3% mean test pass rate at maximum reasoning effort, with estimated API cost $0.77 per sample, versus $3.48 for GPT-5.6 Sol, approximately 78% lower. The benchmark spans 20 languages and counts passing tests, not fully solved production migrations. (source)
DeepSWE v1.1 was the only benchmark captured from the launch announcement (source):
| Model | Effort | Score |
|---|---|---|
| Claude Fable 5 | xhigh | 69.9% |
| GPT-6 Sol | max | 68.8% |
| GPT-6 Luna | max | 66.6% |
| OpenAI's comparison claim is effort-relative and should be read as such: | ||
Luna at max is put level with Opus 5 and Fable 5 at medium effort. That is | ||
| a genuine claim about where a cheap model lands against an expensive one run | ||
| economically, but it is not a claim that Luna matches those models at their | ||
own top settings — Fable 5 at xhigh is 3.3 points ahead in the same table. |
The cost ratios — 93% less per task than Opus 5, 96% less than Fable 5 — are OpenAI's derived figures, not measurements this wiki can check.
The launch snapshot held only the benchmark above; subsequent evaluations are recorded in dated entries in this section. It did not establish separate reasoning, knowledge or multimodal scores.
Use Cases
2026-10-22: the generally available Decisions API offers a separate bounded-answer interface for Luna, including GPT-Live integration. Its input-only billing belongs to that dedicated endpoint; it does not replace the ordinary model API rates in the Spec table. See Model Routing for answer types, price scope and the vendor's latency comparison. (source)
The volume tier of the GPT-6 series: high-throughput coding and agent work where per-task cost dominates. The $0.01/M cached-input rate is the figure that makes this concrete — for workloads that re-read a large stable context, the input side effectively disappears.
Reaching Free and Go users in the desktop app makes Luna the first GPT-6 model on this wiki available outside paid tiers.
Compared To
- GPT-6 Sol — the sibling, launched the same day. 20× the input price and 20× the output price for 2.2 points on DeepSWE v1.1.
- GPT-5.6 Luna — the named predecessor at $0.20/$1.20. GPT-6 Luna halves input and cuts output by roughly 58%. No page on this wiki covers it, and nothing read this run gives it a benchmark figure to compare against.
- Claude Opus 5 and Claude Fable 5 — the models OpenAI chose as its cost comparison. See the effort caveat above.
- MiMo-V2.6-Pro — Xiaomi's MIT-licensed release of the same day. The two are the week's opposite answers to cost: Luna is a cheap proprietary endpoint, MiMo-V2.6-Pro is downloadable weights. They share no benchmark, so the comparison is structural rather than measured.