← ChatGPT & Codex changelog

OpenAI API — April, 2026

New frontier models GPT-5.5 and GPT-5.5 Pro are now available, offering a 1M token context, image input, and a suite of advanced features for complex professional work. A new state-of-the-art image generation and editing model, GPT Image 2, provides flexible image sizes and discounted Batch API support. Enhancements to the Agents SDK include controlled sandboxes and refined memory management. Legacy o3 and o4 deep research models have been deprecated.

Source: official ChatGPT & Codex release notes. Summaries are written from the official notes; see how we work.

Added

  • Released GPT-5.5, a new frontier model for complex professional work, to the Chat Completions and Responses API, and released GPT-5.5 Pro for Responses API requests for tougher problems that benefit from more compute.
  • 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.
  • Updated the Agents SDK with new capabilities, including:

Changed

  • 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:
  • Reasoning effort 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. In-memory prompt caching is not supported. Learn more here.
  • running agents in controlled sandboxes;
  • inspecting and customizing the open-source harness; and
  • controlling when memories are created and where they're stored.

Removed

  • Deprecated o3-deep-research and o4-mini-deep-research, including their June 26, 2025 snapshots. These models are scheduled to shut down on July 23, 2026. See the deprecation notice.

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