Zero-shot CoT
Append 'Let's think step by step.' Kojima et al 2022. Works without examples on large models. Cheap win.
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Few-shot CoT
Provide examples where the reasoning is shown. Model imitates. Stronger than zero-shot CoT on hard tasks.
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Why it works
Generates 'scratchpad' tokens. Model uses them as working memory. Emerges at sufficient scale (~50B parameters historically).
Failure modes
Confidently wrong reasoning. Post-hoc rationalization. Small models fake steps without actual reasoning.