The flagship variant with more compute for the hardest work
Best suited to background mode, long-running reasoning, and tasks that need one request to keep a full evidence chain intact.
Overview
GPT-5.5 Pro is the high-compute member of OpenAI's GPT-5.5 family. It is not positioned as a separate modality tier or a larger-context SKU; it is the version to choose when a single request is valuable enough to trade latency for deeper reasoning, more careful verification, and stronger persistence on hard work.
OpenAI notes that GPT-5.5 Pro requests can take minutes, which makes the Responses API and background mode a natural fit. In CrossModel it keeps the same headline shape as GPT-5.5: 1,050,000 tokens of context, 128,000 output tokens, text and image input, text output, reasoning tokens, and the same tool-oriented API surface.
Key capabilities
| Dimension | Detail |
|---|---|
| Context window | 1,050,000 tokens |
| Max output | 128,000 tokens |
| Input modalities | Text, image |
| Output modalities | Text |
| Best API fit | Responses API with background mode for long-running tasks |
GPT-5.5 Pro does not provide a cached-input discount. Current pricing is kept in the live model catalog, not duplicated in this article.
Pro positioning
Not a larger window, but more willingness to spend compute
GPT-5.5 Pro inherits GPT-5.5 long-context and tool strengths, then aims them at harder, slower, more reliable work.
The simplest way to decide between GPT-5.5 and GPT-5.5 Pro is to ask whether the model should optimize for a crisp answer now or for maximum confidence after more work. GPT-5.5 is the daily flagship for coding, research, and professional output. GPT-5.5 Pro is better reserved for architecture reviews, migration plans, security analysis, contract-heavy comparisons, and research synthesis where the cost of a shallow answer is high.
For product design, that means Pro should rarely sit behind every autocomplete or chat turn. It works better as an escalation target: collect the evidence with cheaper calls, hand the difficult bundle to Pro, and let one long-running request produce the final judgment.
Inherited GPT-5.5 baseline
Pro starts from GPT-5.5 gains on long tasks
These GPT-5.5 launch metrics explain why Pro is a fit for long-context, multi-tool, multi-step verification.
Pro's value depends on the GPT-5.5 baseline. OpenAI reports GPT-5.5 at 82.7% on Terminal-Bench 2.0, 58.6% on SWE-Bench Pro, and a major long-context retrieval gain on MRCR v2 8-needle in the 512K-1M range: 74.0% versus GPT-5.4 at 36.6%. Those are exactly the axes where Pro's extra compute matters: long context, tool coordination, and real engineering loops.
When to use it
- Critical code and architecture review: cross-module correctness, permissions, concurrency, migration risk, and test gaps.
- Long evidence synthesis: combine research packets, contracts, design docs, financial models, and meeting notes into one grounded decision.
- Security and compliance analysis: slow, careful reasoning over high-risk findings with explicit assumptions and audit trails.
- Background agents: tasks that may run for minutes and should return a complete, verified deliverable instead of a quick draft.
CrossModel exposes GPT-5.5 Pro through an OpenAI-compatible API. Current pricing is available in the model catalog.