OpenAI's DevDay 2025 showcased significant advancements in its AI platform, transforming ChatGPT into an operating system that integrates with external services like Canva and Zillow. Key announcements included the launch of the Apps SDK, AgentKit, and Codex, enabling developers to create more sophisticated applications and workflows within the ChatGPT interface. The event featured live demos highlighting the capabilities of these new tools and the API updates, emphasizing OpenAI's commitment to enhancing developer experience.