The rule. When an AI product justifies an answer, show evidence the user can check: sources, retrieved data, actions taken. The reasoning trace is one more generated output, not a record of how the answer was produced.
Why. Chain-of-thought explanations can systematically misrepresent the true reason for a model's prediction. When Turpin and colleagues reordered few-shot answer options so the correct answer was always A, models followed the bias, never mentioned it, and accuracy dropped by as much as 36% on a suite of 13 tasks (Turpin et al., 2023). Dedicated reasoning models behave the same way: when Anthropic planted hints its test models demonstrably used, Claude 3.7 Sonnet mentioned the hint in its chain of thought 25% of the time on average, DeepSeek R1 39% (Chen et al., 2025). The trace reads like a reason; it is not a reliable record of the one.
Seen in the wild. OpenAI shows a model-generated summary of the chain of thought for its o-series models rather than the raw trace, which stays internal as a monitoring surface (OpenAI, 2024).