Originally published on AI Tech Connect.
Key takeaways at a glance This article consolidates several related but separately-timed OpenAI developments. The retirement announcements were confirmed in June 2026; GPT-5.5 Instant became the ChatGPT default in May 2026; GPT-5.3-Codex launched in February 2026. Here is the short version before the detail — along with a clear note on who actually needs to act. GPT-4.5 retires from ChatGPT on 27 June 2026 — less than three weeks from today. This is a ChatGPT product retirement. Custom GPT builders and ChatGPT Enterprise teams must act; raw API developers on GPT-4.5 were already migrated when it was removed from the API in July 2025. o3 retires from ChatGPT on 26 August 2026 — ten weeks away. Again, this is a ChatGPT product retirement. The o3 API has no announced end date; API developers…
