OpenAI Launches GPT-5.5 With 400K Context Window and Faster Fast Mode

OpenAI released GPT-5.5 in March 2025. The model arrives for ChatGPT and Codex users across Plus, Pro, Business, and Enterprise tiers. OpenAI describes the release as the most capable and safe GPT model to date. The company positions the update as a new generation of capabilities for real work.

GPT-5.5 introduces a 400K context window for processing large inputs. The Fast Mode option accelerates token generation by 1.5 times. Users pay a 2.5x cost multiplier for this speed increase. The standard API pricing sets input at $5.00 per 1M tokens. Cached input costs $0.50 per 1M tokens. Output pricing sits at $30.00 per 1M tokens.

OpenAI claims the model improves performance in agent coding, computer use, and knowledge work. The company states these gains occur without slowing speed or using more tokens. Early testers report that ChatGPT handles a wider range of tasks with better quality. Users note significant improvements in sustained workloads.

OpenAI rolls out GPT-5.5 with expanded context and faster speeds

The model excels at multi-step tasks involving planning, tool use, and result verification. OpenAI states the API usage fees are 2x more expensive than GPT-5.4. The release expands the scope of work the system can handle. Users can process more tasks simultaneously with this update.