Machine Learning System Design Interview, issue 9, Nov 28, 2025
The Catastrophic Forgetting Trap
AI Research Engineer interview at OpenAI, and the interviewer asks:
“We deleted our original training dataset for GDPR compliance. We need to teach the live model a new class of data today. How do you do it?”
Why fine-tuning on new data without old samples silently erases your model - and how EWC saves the day.
The full answer, with the mechanism and the arithmetic, is for paid subscribers on Substack.