Learning Steganography Is Easy, Learning Steganographic Reasoning Is Hard
The paper tests whether LLMs can learn to hide useful intermediate reasoning inside innocent-looking outputs, comparing that “steganographic reasoning” against simpler hidden-message passing and overt encoded reasoning under RL, in-context learning, and supervised fine-tuning. The key takeaway is that ordinary steganography and encoded scratchpads are pretty easy to elicit, but covertly embedding reasoning is much harder and usually needs SFT—except when the cover task naturally supports hiding bits—so the work usefully separates nearby threat models, though its conclusions seem sensitive to task design and elicitation setup.
Abstract
Chain-of-thought monitoring as an approach for AI oversight and control is threatened by the possibility of steganographic reasoning, where LLMs conceal their reasoning inside innocuous-looking text. Two neighbouring capabilities, steganographic messaging (passing a concealed message) and encoded reasoning (reasoning in an illegible but unconcealed format), have already been shown to emerge under training pressures that occur in real pipelines, such as reinforcement learning against monitors. This suggests that steganographic reasoning too might arise as an unintended side effect of training. Here, we compare how easily models learn steganographic reasoning and these two neighbouring capabilities across three elicitation methods: reinforcement learning, in-context learning, and supervised fine-tuning (SFT). For most tasks, models learn steganographic reasoning only under SFT, while they learn steganographic messaging and encoded reasoning under all three elicitation methods. Even under SFT, steganographic reasoning requires at least twice as much training as messaging, and for several model-task combinations it is not learned at all. However, on a cover task that makes hiding information especially convenient, steganographic reasoning can be successfully learned under all three elicitation methods. Steganographic reasoning is thus much harder than steganographic messaging and encoded reasoning, and learning the latter two does not imply learning the former. Yet it lies within reach: an easy version is learned under every elicitation method, when the cover task is convenient for hiding information.