← ChatGPT & Codex changelog

OpenAI API — September, 2026

Key highlights of this release include GPT-6 Astra, our most capable model for complex end-to-end tasks, and the public beta of the Agents API for building robust AI agents with managed sessions. Additional features are GPT-Live 1 general availability for voice conversations and new GPT Image 2.5 Sunburst and Flare models for advanced image generation and editing. Developers further benefit from Prompt Cache Diagnostics for GPT-5.6+, new controls for long-running GPT-6 Astra work, and clearer API error differentiation for rate limits.

Added

  • Released the Agents API in public beta. Build agents with a managed Codex harness while OpenAI handles session orchestration, context compaction, and recovery.
  • Released GPT Image 2.5 Sunburst and GPT Image 2.5 Flare for image generation and editing through the Image API and the Responses API image generation tool.
  • Use Sunburst for workflows where editing precision matters most, or Flare for fast, high-quality everyday image generation. Both models support the new xhigh and max quality settings and use GPT Image 2 token rates. See the image generation guide and pricing.
  • Released GPT-6 Astra, our most capable model, built for the hardest end-to-end work.
  • Added new controls for long-running work with GPT-6 Astra in the Responses API:

Changed

  • Use durable sessions to continue work across turns, stream progress, and connect your own tools and MCP servers. Run agents in OpenAI-hosted sandboxes or connect a sandbox from your own infrastructure or a supported provider.
  • Start with the Agents API quickstart.
  • GPT-Live 1 is now generally available in the API. Build full-duplex voice conversations that can continue while a backend model or agent handles reasoning and tools.
  • Use Responses delegation with an OpenAI model, or client delegation to connect your own backend. Voice sessions cost $0.05 per minute, billed per second; backend model and tool usage is charged separately.
  • Start with GPT-Live, prompting, and migration guidance. See pricing for details.
  • Prompt Cache Diagnostics is now generally available in the Responses API for GPT-5.6 and later supported models.
  • Compare cache reuse against a previous response, identify reasons for cache misses, and follow troubleshooting guidance to improve cache reuse.
  • Use GPT-6 Astra for reasoning, coding, computer use, research, and document creation. It combines these capabilities to carry complex tasks from an initial request to a finished result, using the context and tools you provide.
  • Key changes to consider when migrating:
  • GPT-6 Astra does not support the none reasoning effort level.
  • GPT-6 Astra does not support custom temperature or top_p values or log probabilities (logprobs).
  • Tool calling requires the Responses API. If you use tools with Chat Completions, follow the Responses migration guide.
  • Misalignment monitoring asynchronously checks for potential issues during agent work in supported Responses API requests. Checks can trigger safety alerts or stop a conversation for review.
  • Start with Using GPT-6 Astra for capabilities, prompting, and migration guidance. Explore computer use for browser and desktop workflows, and see pricing for available inference tiers.
  • Async tool calling: Let the model continue working while your application runs function or custom tools, then return results as they become available.
  • Mid-turn steering: Send additional instructions while a response is in progress over WebSockets, so the model can incorporate corrections or changing requirements.
  • Change reasoning effort mid-conversation: Increase effort for difficult work or reduce it for routine follow-ups while preserving the cached prompt prefix.
  • Updated API errors so applications can distinguish traffic that increases too quickly from temporary model overload.
  • Traffic that increases too quickly can return a 429 error with the slow_down code. Temporary model overload returns a 503 error with the server_is_overloaded code. Both responses may include Retry-After. When the header is present, wait at least as long as it specifies before retrying. If it's missing, use exponential backoff. See the error codes guide and rate limits guide.
  • Connections to api.openai.com can now use IPv6.