GPT-5.5
The latest OpenAI flagship — premium reasoning with 256K context.
via OpenAI →
What is this model?
GPT-5.5 is OpenAI's flagship model launched in April 2026, as successor to the GPT-5 series. It combines the multimodal capabilities of GPT-4o with the deep reasoning of the o-series, in one unified model. With 256K context window (the largest in our catalog) and strong performance on all major benchmarks (MMLU-Pro, GPQA, AIME), this is OpenAI's answer to the top-tier models from Anthropic and Google.
Strengths
Strengths: 256K context window (50% larger than Claude Opus 4), unified multimodal+reasoning architecture, strong in long-form analysis, native tool use, and the best OpenAI performance on coding benchmarks. For "I want absolute top OpenAI quality and cost is secondary" this is the right pick.
Best suited for
- Research, deep dives and analyses
- Long documents and summaries
- Complex reasoning and multi-step tasks
How ZelixAI uses this model
GPT-5.5 is the premium "all-in-one" pick within ZelixAI: for customers who want more quality than GPT-4o offers, without the latency tradeoff of o3, and with a 200K+ context window for RAG workflows with large knowledge bases. Watch costs — this is our most expensive OpenAI model.
Real-world examples within ZelixAI
Real example: a media company runs full annual reports (200K+ tokens) through GPT-5.5 for automatic summaries and risk analyses. A software house uses it for architecture reviews — load an entire microservice codebase and ask GPT-5.5 to identify bottlenecks and security issues. A research institute uses it for literature reviews where 50+ scientific papers fit in one context window.
Limitations and caveats
Limitations: highest OpenAI cost in our catalog (~$5/1M input). Recent launch (April 2026) — less long in production validated than GPT-4o. US cloud provider — not for strict EU data residency. For real-time chat it's overkill; use GPT-4o mini instead.
Technical specifications
| Provider | OpenAI |
| Context window | 256K tokens |
| Throughput | 15–40 tokens/s (Average) |
| Cost tier | Premium |
| Tool / function-calling | yes |
| Data residency | United States (cloud provider) |