A probe can predict when a model will follow a misleading hint, but not whether the hint caused the answer

Language models often follow a misleading hint without saying so in their chain of thought (CoT); such a CoT is called unfaithful. This matters for safety because reading the CoT is one way to catch a misaligned model, which works only if the CoT shows what drove the answer. On Qwen3 0.6B to 8B, I trained linear probes on hidden states to predict hint-following, then tested two things: whether the probe signal is causal, and whether a probe can tell when the hint caused the answer, which is what makes a CoT unfaithful.