ChatGPT's Biggest Upgrade Ever: What Developers Actually Need to Know [June 2026] (opens in new tab)

OpenAI has shipped more developer-facing infrastructure in the first half of 2026 than in the prior two years combined. GPT-5.5 is live. The Agents SDK is production-ready. Codex hit 5 million weekly active users. And yet most of the coverage is about ChatGPT's chat UX. Let's skip that and talk about what actually matters: ChatGPT's biggest upgrade ever and what developers actually need to know in June 2026. What changed at the API layer, which features are production-grade versus demo-ware, ...