Nature: LLMs transmit behavioural traits through hidden signals embedded in training data

A new Nature paper (s41586-026-10319-8) finds that language models encode and propagate behavioural traits — including biases, reasoning styles, and tendencies — through hidden signals in training data, not just through explicit content. The mechanism persists across fine-tuning and is not detectable by standard alignment audits. Published in Nature, the study has immediate implications for how model providers understand inheritance of behaviour between model generations and base-model contamination.