OpenAI releases GPT-5.5 and GPT-5.5 Pro in API

OpenAI has released GPT-5.5, a new frontier model for complex professional work, to the Chat Completions and Responses API. The company also released GPT-5.5 Pro for Responses API requests for tougher problems that benefit from more compute. GPT-5.5 supports a 1M token context window, image input, structured outputs, function calling, prompt caching, Batch, tool search, built-in computer use, hosted shell, apply patch, Skills, MCP, and web search. Key updates include a reasoning effort that now defaults to medium. When image_detail is unset or set to auto, the model now uses original behavior. Caching for GPT-5.5 only works with extended prompt caching, while in-memory prompt caching is not supported. The company also released GPT Image 2, a state-of-the-art image generation model for image generation and editing. GPT Image 2 supports flexible image sizes, high-fidelity image inputs, token-based image pricing, and Batch API support with a 50% discount. OpenAI updated the Agents SDK with new capabilities, including running agents in controlled sandboxes, inspecting and customizing the open-source harness, and controlling when memories are created and where they are stored. In March 2026, OpenAI released GPT-5.4 mini and GPT-5.4 nano to the Chat Completions and Responses API. GPT-5.4 mini brings GPT-5.4-class capabilities to a faster, more efficient model for high-volume workloads, while GPT-5.4 nano is optimized for simple high-volume tasks where speed and cost matter most. GPT-5.4 mini supports tool search, built-in computer use, and compaction, while GPT-5.4 nano supports compaction but does not support tool search or computer use. Also in March, the company expanded the Sora API with reusable character references, longer generations up to 20 seconds, 1080p output for sora-2-pro, video extensions, and Batch API support for POST /v1/videos. Generations on sora-2-pro are billed at $0.70 per second. Earlier in March, OpenAI released GPT-5.4 and GPT-5.4 Pro. The release included tool search in the Responses API, which lets models defer large tool surfaces until runtime to reduce token usage and improve latency. The release also included built-in Computer use support in GPT-5.4 through the Responses API computer tool for screenshot-based UI interaction, along with a 1M token context window and native compaction support for longer-running agent workflows.