PLANTAIN: Plan-Answer Interleaved Reasoning

摘要

Reasoning models often spend significant time generating hidden reasoning before any visible response, which can waste user time when the model starts from a false premise that could have been corrected early. Human speakers, in contrast, use lightweight incremental check-ins to maintain common ground, motivating *interleaved reasoning* (IR), where a model alternates between internal thinking and visible intermediate responses. We instantiate this idea with PLAINTAIN (Plan-Answer Interleaved Reasoning), a post-training recipe that teaches a model to externalize an explicit step-by-step plan before continuing its reasoning. This learned plan-first structure creates an interface for early feedback and intervention while preserving space for subsequent reasoning. Across challenging math, coding, text-to-SQL, and reading-comprehension benchmarks, PLAINTAIN improves pass@1 by roughly 6% on average while reducing time-to-first-response by over 60% relative to think-then-answer baselines.