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Inference-Time Intervention: Eliciting Truthful Answers from a Language Model

Written for the Research library (claude-opus-5-5) from the paper text. Original — arxiv.org/pdf/2306.03341

Summary

Large language models often say false things even when their internal activations seem to hold the correct answer. The authors tested LLaMA-7B on TruthfulQA. Linear probes reading its intermediate activations told true answers from false ones far more reliably than the model's own generations did, with a gap of about 40%. To use this hidden signal, they propose Inference-Time Intervention (ITI). A logistic probe is trained on the output of each attention head, and the few heads where truthfulness is easiest to read linearly are kept. At every decoding step, those heads' activations are shifted along the learned "truthful" direction. ITI needs no fine-tuning, only a few hundred labelled QA pairs and very little extra compute. On LLaMA, Alpaca and Vicuna it clearly raises TruthfulQA scores, and Alpaca's truthfulness roughly doubles. A single strength parameter trades truthfulness against informativeness. The method is a cheap, adjustable alternative or complement to RLHF. It also suggests that models keep an internal sense of what is true that ordinary decoding fails to bring out.

Key points

  • Data: the 817 TruthfulQA questions (38 categories) were split into 5,918 QA pairs, each labelled true or false. Probes use last-token head activations with a 4:1 train/validation split.
  • Headline result: Alpaca's truthfulness on TruthfulQA rose from 32.5% to 65.1%. Truthful directions plateau quickly, and as few as 40 samples are enough to locate useful heads.
  • Sparsity matters. On LLaMA-7B, choosing whole heads (True*Info 42.3%) beat intervening on all heads (35.4%) and choosing individual features (39.2%). Probing all heads together (84.4%) is only slightly better than the best single head (83.3%).
  • Without retuning, LLaMA-7B + ITI improved on out-of-distribution sets: Natural Questions 46.6→51.3, TriviaQA 89.6→91.1, MMLU 35.71→40.16.
  • Code is released as honest_llama (github.com/likenneth/honest_llama). The paper was published at NeurIPS 2023.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

Fields: Other

Cited by

371 papers of our library cite it (of the 140673 whose bibliographies we read); 17 of them have a page here, 354 not yet.

Cite

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.48550/arxiv.2306.03341 · arXiv 2306.03341

@misc{li2023inference,
  title = {{Inference-Time Intervention: Eliciting Truthful Answers from a Language Model}},
  author = {Li, Kenneth and Patel, Oam and Viegas, Fernanda and Pfister, Hanspeter and Wattenberg, Martin},
  year = {2023},
  doi = {10.48550/arxiv.2306.03341},
  eprint = {2306.03341},
  archivePrefix = {arXiv},
  url = {https://doi.org/10.48550/arxiv.2306.03341}
}

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