Character.AI MLE Interview Questions (2026)

Questions reported from Character.AI machine learning engineer interviews. This bank tracks 8 questions asked at Character.AI (5 with free model answers). Practice them live with DeepOffer's AI voice interviewer.

← All 465 questions

Practice this question with an AI interviewer

Get asked follow-ups live, then receive a scored report — like a real MLE interview loop.

Start AI mock interview

#43 Describe the KV cache, derive its memory formula, and discuss what it costs at production scale. ★
#169 Explain prefix/prompt caching: when to use it and what invalidates a cached prefix. ★
#170 Compare FP16, BF16, FP8, INT8, INT4, and FP4 for serving and name what breaks at each step down. ★
#195 Estimate what one message costs to serve and identify which lever moves that cost most. ★
#196 Our serving cost is dominated by KV cache, not weights — cut it by an order of magnitude and name what you give up.
#197 Design the cache that sits between turns for dialogues averaging ~180 messages.
#242 Design guardrails for a consumer-facing assistant: input filters, output filters, or both? ★
#251 Design the safety system for open-ended character chat.