OpenAI
GPT-5.6 Luna: price, context window, and caching
The low-cost GPT-5.6 tier for cost-sensitive, high-volume work, which roughly corresponds to earlier GPT-5 nano models.
Released July 9, 2026 · Prices as of September 28, 2026
In OpenAI’s words
“GPT-5.6 model optimized for cost-sensitive workloads”
Facts
Specs and prices
| Fact | GPT-5.6 Luna |
|---|---|
| Maker | OpenAI |
| API model id | gpt-5.6-luna |
| Released | July 9, 2026 |
| Status | Previous generation |
| Context window | 1.05M tokens |
| Max output | 128K tokens |
| Open weights | No |
| Input, per 1M tokens | $0.20 |
| Cache hit, per 1M | $0.02 |
| Cache write, per 1M | $0.25 |
| Output, per 1M tokens | $1.20 |
| Runs in | Codex, Cursor, OpenCode, OpenRouter, and GitHub Copilot |
Standard API rates in US dollars, as published by the maker on September 28, 2026. Batch and priority tiers, taxes, and subscription plans are not included. GPT-5.6 Luna: Requests over 272K input tokens cost 2x for input and cache and 1.5x for output, for the whole request.
Good to know
- Codex suggests moving to GPT-6 Luna. It stays available in the API.
- OpenAI cut its price by 80% on July 30, 2026.
Cost
What typical work costs
Example token counts at GPT-5.6 Luna’s published rates. On the agentic session, caching saves $0.34 against billing every token as ordinary input.
| Agentic coding session, 100K input, 400K written to cache, 2M read from cache, 50K output | $0.22 |
|---|---|
| Large one-off review, 150K input with no cache hits, 10K output | $0.04 |
| Output-heavy generation, 30K input, 80K output | $0.10 |
| A month of sessions, 110 sessions: 5 a day, 22 working days | $24.20 |
Prompt caching
How OpenAI bills cached tokens
OpenAI
Prompt caching is on by default. From GPT-5.6 on you can also mark up to four explicit cache breakpoints, while GPT-5.5 and earlier cache automatically only.
From GPT-5.6 on, a cache write costs 1.25x the uncached input price and a cache hit costs 0.1x. GPT-5.5 and earlier add no charge for writing the cache: written tokens are billed as ordinary input, and a hit costs 0.1x on the models compared here.
On GPT-5.6 and later, a cached prefix stays reusable for at least 30 minutes after its last use, and caching starts at 1,024 input tokens.
Source: OpenAI: Prompt caching
GPT-5.6 Luna compared
Claude Haiku 4.5 vs GPT-5.6 Luna
After an 80% price cut, GPT-5.6 Luna costs a fifth of Claude Haiku 4.5 for input. A month of cached coding sessions: $24.20 against $132.00.
DeepSeek-V4.1-Flash vs GPT-5.6 Luna
DeepSeek-V4.1-Flash and GPT-5.6 Luna both price a cached coding session at $0.22, from opposite ends: Luna's cheaper input, DeepSeek's cheaper cache hits.
GPT-5.6 Luna vs Gemini 3.5 Flash-Lite
Gemini 3.5 Flash-Lite costs 1.5x as much as GPT-5.6 Luna on a cached coding session, $0.34 against $0.22, and about twice as much on output-heavy work.
GPT-5.6 Terra vs GPT-5.6 Luna
GPT-5.6 Terra costs 10x GPT-5.6 Luna on every rate after OpenAI's July 30 price cuts. What each tier is for, and why Codex now sends them different ways.
GPT-6 Luna vs GPT-5.6 Luna
GPT-6 Luna halves the input price of GPT-5.6 Luna, which already had an 80% cut, and trims output further. What the move saves, and what Codex suggests.
Your own numbers
See what GPT-5.6 Luna really costs you.
everyaitoken reads your Codex, Cursor, OpenCode, and OpenRouter history on your Mac and prices every request at API rates, with what caching saved or cost. $9 once.