Summary
OpenAI's April 23, 2026 GPT-5.5 launch rolled the model out to ChatGPT and Codex and positioned it as the company's strongest agentic coding model to date. OpenAI's developer docs also show GPT-5.5 Pro is available in the Responses API with a 1,050,000-token context window, 128,000 max output tokens, and tool support for web search, file search, image generation, code interpreter, hosted shell, and MCP.
What changed
OpenAI launched GPT-5.5 and GPT-5.5 Pro, rolled GPT-5.5 to Plus, Pro, Business, and Enterprise users in ChatGPT and Codex, and exposed GPT-5.5 Pro in the Responses API with a 1.05M context window and advanced tool support.
Why it matters
This is not just another flagship model refresh. By tying GPT-5.5 directly to Codex and exposing GPT-5.5 Pro as a large-context API model with agent-oriented tool support, OpenAI is strengthening both the product surface and the programmable backend for long-horizon coding workflows.
Evidence excerpt
OpenAI's developer docs say GPT-5.5 Pro is available for Responses API requests with a 1,050,000 context window and advanced tool support.