Probes detect motivated reasoning before and after chain-of-thought

Mirtaheri & Belkin use a paired hinted/unhinted framework to label motivated reasoning across Qwen3-8B, Llama-3.1-8B-Instruct, and Gemma-3-4B, probing activations with recursive feature machines [mirtaheri-belkin-2026-catching-rationalization-in-the-act-detecting-motivated-reasoning-before-and-after-cot-via-activation-probing] Pre-generation probes match a GPT-5-nano full-trace CoT monitor and post-generation probes outperform it [mirtaheri-belkin-2026-catching-rationalization-in-the-act-detecting-motivated-reasoning-before-and-after-cot-via-activation-probing] A hint-recovery probe shows a U-shaped accuracy curve across CoT tokens, so the model internally re-engages the hinted answer even when its CoT never mentions it [mirtaheri-belkin-2026-catching-rationalization-in-the-act-detecting-motivated-reasoning-before-and-after-cot-via-activation-probing]