GPT-5.5 Pro

OpenAI·Apr 2026reasoningproprietary

GPT-5.5 Pro is the high-compute variant of GPT-5.5 that spends substantially more inference-time reasoning on every request. It targets frontier research questions, competition-grade math and gnarly debugging sessions where a single correct answer is worth far more than latency or cost. At $30 per million input tokens and $180 per million output tokens it is one of the most expensive APIs on the market, so most teams reserve it for verification passes and the hardest few percent of tasks.

Benchmark results

No verified benchmark results tracked yet for GPT-5.5 Pro. This page is updated as official evaluations are published.

Where it shines

  • Best-available answer quality on extremely hard problems
  • Deep multi-step reasoning with extended thinking budgets
  • Useful as a verifier/escalation tier above GPT-5.5

Alternatives to GPT-5.5 Pro

Qwen3-Max

Alibaba's trillion-parameter API flagship — frontier-adjacent quality with strong agentic tool use at mid-tier prices.

Gemini 3 Pro

Google's November 2025 frontier breakout — 91.9% GPQA Diamond and 37.5% HLE made it the reasoning leader of its generation.

Gemini 2.5 Pro

Google's 2025 workhorse flagship — first mainstream thinking model with a 1M context, still widely deployed.

DeepSeek V3.2

The sparse-attention release that halved DeepSeek's already-lowest-in-class prices while keeping GPT-class quality.

Frequently asked questions

How much does the GPT-5.5 Pro API cost?
GPT-5.5 Pro costs $30 per million input tokens and $180 per million output tokens. A workload of 10M input and 1.5M output tokens per month costs about $570.00.
What is the context window of GPT-5.5 Pro?
GPT-5.5 Pro supports a context window of 1,000,000 tokens (1M), with up to 128K output tokens per response.
Is GPT-5.5 Pro open source?
No — GPT-5.5 Pro is a proprietary model available through OpenAI's API and partner platforms.
What are the best alternatives to GPT-5.5 Pro?
The closest alternatives by overall capability are Qwen3-Max, Gemini 3 Pro, Gemini 2.5 Pro, DeepSeek V3.2. See the comparison pages for detailed head-to-head breakdowns.