EP050 — It Decides Before It Stops Talking (Commitment Boundary)

When a reasoning model 'thinks out loud,' it usually locks onto its final answer at a sharp, detectable point — a commitment boundary — often in a single step and well before the reasoning block ends. The steps it writes after that point are epiphenomenal: they leave the answer unchanged, and a small internal probe can spot the boundary and cut the reasoning short — reportedly by more than half — with almost no loss in accuracy. It matters because monitoring a model's chain of thought for safety may be reading theater: the tokens that actually decided the answer are upstream of where oversight tends to look, and nothing on the surface marks the switch. The cross-domain parallel is the neuroscience of decision-before-narration — Benjamin Libet's finding that instruments can detect a choice forming in the brain before the person reports deciding, and the confident after-the-fact explanations people give for choices that weren't driven by the reasons they cite. Machine's Learning is a Plumbline Tools production. Support the show: https://plumbline.tools/podcast/