Proactively Migrate Legacy Custom Instructions Before Model Retirement Deadlines
Prepare for the retirement of GPT-4.5 and o3 legacies today.
Update your custom instructions and workflows before the June and August 2026 deadlines to ensure the GPT-5 series models match your required output style.
The Scenario
You have built a specific workflow or custom instruction set around GPT-4.5 or o3 and need to ensure your productivity isn't disrupted when these models are retired.
Before & after
Developers might rely on legacy endpoints like GPT-4.5 or o3 indefinitely, only to have their applications break unexpectedly when the 30-day or 90-day sunset period ends.
Migrate your API calls to GPT-5.5 or higher immediately. This update takes about 10–15 minutes of dev time but prevents service outages.
The Prompt
Review my current custom instructions for GPT-4.5: [PASTE_INSTRUCTIONS]. Transition these to be optimized for GPT-5.6 reasoning and GPT-5.5's natural style to maintain my brand voice.
GPT-4.5 is scheduled for retirement from ChatGPT on June 27, 2026, and o3 on August 26, 2026. While API changes vary, the migration of ChatGPT conversations to newer models suggests users should proactively move their custom workflows to GPT-5 series models to maintain continuity in writing style and functionality.
Source
Model Release Notes | OpenAI Help Center"OpenAI o3 will be retired from ChatGPT on August 26, 2026... and GPT-4.5 will be retired from ChatGPT on June 27, 2026."