OpenAI DevDay 2025: AgentKit, Apps SDK and Codex general availability

Background

DevDay is OpenAI's developer conference. The 2025 edition was held in San Francisco on 6 October 2025.^[1][3]

What happened

At the event Sam Altman said that ChatGPT had more than 800 million weekly users, that 4 million developers had built with OpenAI and that the API processed over 6 billion tokens per minute.^[1]

Altman announced AgentKit, a set of tools built on the Responses API. It included Agent Builder, ChatKit, a Connector Registry, enhanced Evals, Guardrails and reinforcement fine-tuning.^[2] Evals are tests that measure how well a model performs a task, and guardrails are checks that limit what an agent may do or output.

OpenAI also announced the Apps SDK, which lets developers build apps that run inside ChatGPT, and made Codex generally available.^[3]

Key details

New API models included GPT-5 Pro, gpt-realtime-mini and gpt-image-1-mini. Sora 2 came to the API at the same event.^[3][4]

The same day AMD and OpenAI announced a partnership to deploy 6 gigawatts of AMD GPUs.^[5] A GPU is a graphics processor, which is the kind of chip commonly used to run large AI models.

Impact

For developers, the event brought together several tools into one stack: models in the API, a framework for agents built on the Responses API, and a way to build apps that appear inside ChatGPT. Codex moved from a preview to general availability in the same announcement.^[3]

A developer conference is where a company presents its developer offerings together, so the announcements above should be read as a set of product and platform changes made on one day.

The usage figures Altman cited describe the platform at the time of the event rather than a forecast of future growth.

Partnerships such as the AMD agreement affect where a company's models run, because the chips that serve them come from the partner.