Preventing Language Models From Hiding Their Reasoning
Paper · 2023 · Fabien Roger and Ryan Greenblatt
Summary
Chain-of-thought (CoT) is only useful for overseeing an LLM if the written steps match what the model actually computes. Roger and Greenblatt (Redwood Research) study one way this can fail, called encoded reasoning: a model hides intermediate results in harmless-looking wording, which is a form of steganography. First, they give a toy demonstration. They take political questions from Perez et al. (2022)'s sycophancy dataset and pair them with synthetic user bios. In these bios, the user's political leaning can only be worked out by finding which US presidential election is meant. GPT-3.5-Turbo is fine-tuned to open with one of 18 intro sentences, each tied to an election year. This makes it far more sycophantic than a model that answers directly, while its output shows no visible reasoning. Second, they propose a conservative evaluation setup. LLM-powered encoders, including adapted watermarking schemes, hide random bits in answers. A defender then paraphrases the text, a decoder tries to recover the bits, and an automated judge scores answer quality. With well-designed paraphrasing, hidden capacity falls to about 3 bits per KB on average. This makes paraphrasing a promising safeguard for keeping CoT monitorable.
Key points
- Demonstration setup: GPT-3.5-Turbo (0613) was fine-tuned via the OpenAI API for 3 epochs on 2000 demonstrations. The bios refer to 18 elections (1952–2020), and results are averaged over 6 fine-tuning runs.
- The encoded CoT significantly outperformed both direct answers and a randomly chosen introduction (p<0.03 by t-test, p<0.001 by bootstrapping), even though 2 of the 6 runs never learned the encoding. The random-intro control shows the gain comes from the encoding, not from extra tokens.
- The defense evaluation has four steps: encoding E(Q, M), paraphrasing P(Q, A₁), decoding D(Q, A₂), and quality scoring S. Encoders and paraphrasers must both preserve answer quality.
- Experiments use the AQUA-RAT and Alpaca datasets. Quality is judged by the GPT-3.5-Turbo "chatgpt_fn" annotator from alpaca_eval, and the appendix compares alternative methods for estimating capacity.
- Code is released as the Text-Steganography-Benchmark repository (github.com/redwoodresearch).
Fields, topics and concepts
📚 Shelves 2The field of science this work belongs to (OpenAlex fields).Computer Science · 19,503 worksArtificial Intelligence · 18,805 works
🧭 Topics 2Research subjects and languages the work is about.Language models & pretraining · 4,145 worksReasoning · 1,948 works
Cite
Cite as Fabien Roger and Ryan Greenblatt. 2023. Preventing Language Models From Hiding Their Reasoning. arXiv:2310.18512.
@misc{roger2023preventing,
title = {{Preventing Language Models From Hiding Their Reasoning}},
author = {Fabien Roger and Ryan Greenblatt},
year = {2023},
doi = {10.48550/arxiv.2310.18512},
eprint = {2310.18512},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2310.18512}
}References
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