GPT-5.5 Pro

• 🆕 OpenAI's most advanced Pro reasoning model, released April 2026
• 🧠 Built on GPT-5.5's unified architecture, tuned for high-stakes tasks
• 📏 1M+ token context window (922K input, 128K output)
• 👁️ Accepts text and image inputs
• 🔧 Supports function calling, web search, and agentic tool use
• ⚡ Spends extra compute to "think harder" for precise answers
• 🎯 Designed for tough problems needing top-tier reasoning

OpenAI

OpenAI is an American artificial intelligence research organization headquartered in San Francisco, structured as both a for-profit public benefit corporation and a nonprofit foundation. The lab developed the GPT family of large language models, the DALL-E…

GPT-5.5 Pro is the highest-effort variant of OpenAI's GPT-5.5 generation, released April 24, 2026, one day after standard GPT-5.5. OpenAI describes it as a version of GPT-5.5 that "produces smarter and more precise responses," using more compute to think harder and deliver consistently better answers on tough problems. Like its predecessors, it runs through the Responses API to support multi-turn interactions, and some requests may take several minutes to complete. It carries a 1M+ token context window and accepts both text and image inputs.

Compared to its same-family predecessor GPT-5.4 Pro, GPT-5.5 Pro inherits the gains OpenAI reports for the GPT-5.5 base over GPT-5.4. OpenAI says GPT-5.5 reaches strong results with fewer reasoning tokens than prior models at the same reasoning effort, which compounds savings in tool-heavy, multi-step workflows. The company also notes a clear improvement over GPT-5.4 on GeneBench, a new evaluation focused on multi-stage scientific data analysis in genetics and quantitative biology.

OpenAI positions GPT-5.5 as its flagship for complex reasoning and coding, with particular gains in agentic coding, computer use, knowledge work, and early scientific research. The 1M-token window makes full-codebase analysis and large-corpus reasoning more tractable without elaborate chunking.

The Pro tier is intended for the narrower set of high-value, high-stakes scenarios that genuinely need top-tier reasoning, rather than everyday workloads. Teams typically reserve it for specific high-stakes pipelines while using standard GPT-5.5 as the default.