OpenAI
GPT-5.6 Sol: price, context window, and caching
The flagship of the July 2026 GPT-5.6 family, now succeeded by GPT-6 Sol and on promotional pricing.
Released July 9, 2026 · Prices as of September 28, 2026
In OpenAI’s words
“Flagship model for complex professional work”
What OpenAI says it’s good at
Facts
Specs and prices
| Fact | GPT-5.6 Sol |
|---|---|
| Maker | OpenAI |
| API model id | gpt-5.6-sol |
| Released | July 9, 2026 |
| Status | Previous generation |
| Context window | 1.05M tokens |
| Max output | 128K tokens |
| Open weights | No |
| Input, per 1M tokens | $4 |
| Cache hit, per 1M | $0.40 |
| Cache write, per 1M | $5 |
| Output, per 1M tokens | $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 Sol: Requests over 272K input tokens cost 2x for input and cache and 1.5x for output, for the whole request. These are promotional rates, available at least through November 21, 2026.
Good to know
- Codex cloud chats on ChatGPT plans use it, and Codex suggests moving to GPT-6 Sol elsewhere.
- The API id gpt-5.6 points to it.
Cost
What typical work costs
Example token counts at GPT-5.6 Sol’s published rates. On the agentic session, caching saves $6.80 against billing every token as ordinary input.
| Agentic coding session, 100K input, 400K written to cache, 2M read from cache, 50K output | $4.20 |
|---|---|
| Large one-off review, 150K input with no cache hits, 10K output | $0.80 |
| Output-heavy generation, 30K input, 80K output | $1.72 |
| A month of sessions, 110 sessions: 5 a day, 22 working days | $462.00 |
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 Sol compared
Claude Fable 5.1 vs GPT-5.6 Sol
GPT-5.6 Sol costs 60% less than Claude Fable 5.1 at promotional rates available at least through November 21, 2026. Why caching leaves the 2.5x gap intact.
Claude Opus 5 vs GPT-5.6 Sol
Claude Opus 5 lists 25% above GPT-5.6 Sol, and Anthropic's 1-hour cache writes stretch that to 43% on a coding session. Promotions, long context, successors.
Claude Opus 5.5 vs GPT-5.6 Sol
Claude Opus 5.5 and GPT-5.6 Sol share $4 input and $20 output prices. Cache rules decide the rest: a coding session costs $4.40 on Opus 5.5 and $4.20 on Sol.
Claude Sonnet 5 vs GPT-5.6 Sol
GPT-5.6 Sol charges twice Claude Sonnet 5's rates on promotional pricing that runs through at least November 21, 2026. A cached session: $4.20 vs $2.40.
GPT-5.6 Sol vs Gemini 3.1 Pro Preview
GPT-5.6 Sol is on promotional rates and Gemini 3.1 Pro Preview is still in preview. On a cached coding session, Gemini costs $2.00 against $4.20.
GPT-5.6 Sol vs GPT-5.5
GPT-5.6 Sol cuts GPT-5.5's rates but adds a 1.25x charge for cache writes. Why the session gap is 16%, not 20%, and what changes on October 14.
GPT-5.6 Sol vs GPT-5.6 Terra
GPT-5.6 Sol costs about twice GPT-5.6 Terra, on promotional rates. How Terra's output price narrows the gap and why Codex points both to GPT-6 Sol.
GPT-6 Sol vs GPT-5.6 Sol
GPT-6 Sol costs half as much as GPT-5.6 Sol on every rate, and Codex suggests the move. What changes, what the promo pricing means, and what stays put.
Your own numbers
See what GPT-5.6 Sol 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.