OpenAI
GPT-5.5: price, context window, and caching
OpenAI's April 2026 flagship for coding and professional work, now a previous generation that stays in the API.
Released April 23, 2026 · Prices as of September 28, 2026
In OpenAI’s words
“A new class of intelligence for coding and professional work.”
What OpenAI says it’s good at
Facts
Specs and prices
| Fact | GPT-5.5 |
|---|---|
| Maker | OpenAI |
| API model id | gpt-5.5 |
| Released | April 23, 2026 |
| Status | Previous generation |
| Context window | 1.05M tokens |
| Max output | 128K tokens |
| Open weights | No |
| Input, per 1M tokens | $5 |
| Cache hit, per 1M | $0.50 |
| Cache write, per 1M | $5 (same as input) |
| Output, per 1M tokens | $30 |
| 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-5.5: Prompts over 272K input tokens cost 2x for input and 1.5x for output, for the full session.
Good to know
- It leaves ChatGPT and Codex sign-in on October 14, 2026, and stays in the API.
Cost
What typical work costs
Example token counts at GPT-5.5’s published rates. On the agentic session, caching saves $9.00 against billing every token as ordinary input.
| Agentic coding session, 100K input, 400K written to cache, 2M read from cache, 50K output | $5.00 |
|---|---|
| Large one-off review, 150K input with no cache hits, 10K output | $1.05 |
| Output-heavy generation, 30K input, 80K output | $2.55 |
| A month of sessions, 110 sessions: 5 a day, 22 working days | $550.00 |
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-5.5 compared
Claude Opus 4.8 vs GPT-5.5
Claude Opus 4.8 and GPT-5.5 share a $5 input price, yet GPT-5.5 costs less on cached sessions and Opus 4.8 less on output-heavy work. Where the crossover falls.
Claude Opus 5.5 vs GPT-5.5
Claude Opus 5.5 undercuts GPT-5.5 on input, output, and cache hits, yet a cached coding session is only 12% cheaper. GPT-5.5 leaves Codex sign-in soon.
Claude Sonnet 5 vs GPT-5.5
GPT-5.5 costs 2.5x Claude Sonnet 5 for input and 3x for output, and it leaves ChatGPT and Codex sign-in on October 14, 2026. What that means for coding.
GPT-5.5 vs Gemini 3.1 Pro Preview
GPT-5.5 costs 2.5x as much as Gemini 3.1 Pro Preview on every rate and every workload. Where they differ instead: output limits, long prompts, and access.
GPT-5.5 vs GPT-5.4
GPT-5.5 costs exactly twice GPT-5.4 on every rate, and both are leaving Codex sign-in. What the 2x gap means for API users and where Codex points instead.
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-6 Astra vs GPT-5.5
GPT-6 Astra doubles GPT-5.5's input price and adds a 1.25x cache-write charge GPT-5.5 never had. What that does to agentic sessions and to Codex.
Your own numbers
See what GPT-5.5 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.