Everything about GPT-5.5 Pro

GPT-5.5 Pro at a glance

Released on April 23, 2026, GPT-5.5 Pro is one of the 16 OpenAI models tracked on this site. It is a closed model: you access it through an API, from OpenAI or one of the 20 providers listed on models.dev. It has a reasoning mode: it can "think" before answering, which helps with multi-step problems but uses more tokens, and therefore more money. That makes it 6 months old as of October 22, 2026.

We file it under frontier models (24 models in this category on the site).

What do independent benchmarks say?

According to results published by Epoch AI (checked on October 22, 2026), GPT-5.5 Pro has a capability index of 96.9 out of 100, computed on 3 benchmarks from our basket.

With only 3 benchmarks reported, it does not enter the public ranking, which requires at least 4 results, so its index should be read as partial.

• GPQA Diamond (PhD-level science questions): 93.9% — the best tracked model, Gemini 4 Argon, reaches 96.4%
• OTIS Mock AIME (competition mathematics problems): 100% — best score among tracked models
• FrontierMath (very hard research-level mathematics): 87.7% — the best tracked model, GPT-6 Astra, reaches 93.7%

Technical specifications

Its context window reaches 1,050,000 tokens, roughly 1,575 pages of text at 500 words per page: enough to load a whole book or a mid-sized codebase. A single answer can run to 100,000 tokens.

It accepts as input: text, image and PDF. Its knowledge stops at December 1, 2025: beyond that, it needs web search or your documents.

It can call tools (functions, APIs) and return structured JSON output, which makes it a possible foundation for an AI agent.

How much does GPT-5.5 Pro cost?

GPT-5.5 Pro costs $30 per million input tokens and $180 per million output tokens (median of 20 providers, checked on October 22, 2026).

To put it in perspective: reading 20,000 tokens (about thirty pages) and writing 2,000 costs roughly $0.96; a thousand of those tasks, $960.

That is 12.4 times the median output price of frontier models ($14.5).

To estimate your own budget, use the agent cost calculator.

What is it good for?

Given its category, GPT-5.5 Pro is mainly aimed at hard tasks where quality matters more than cost: deep reasoning, complex code, long analyses.

Its very large context window makes it worth considering for analysing large sets of documents in a single request.

Before adopting it, test it on your own examples: benchmarks measure standard tasks, not your job.

Alternatives

In the same category, the models closest to GPT-5.5 Pro are:

• Claude Sonnet 5.5 (Anthropic, index 95.9) — see the comparison
• Claude Opus 5.5 (Anthropic, index 95.9) — see the comparison
• Gemini 4 Argon (Google DeepMind, index 95.3) — see the comparison
• GPT-6 Astra (OpenAI, index 94.7) — see the comparison