Instruction tuning erodes semantic diversity, and bigger models lose more

burkov · x · 2026-11-08

Instruction tuning helps LLMs follow directions and produce useful responses, but it reduces the semantic diversity of outputs — and the loss grows with scale: larger base models cover a broader range of content, while larger instruction-tuned models become more homogeneous. Since diversity underlies serving varied prompts and producing genuinely different ideas, this matters.

The article proposes annotation-anchored training: models learn to emit short tags describing content during pretraining, and during instruction tuning updates are anchored to this explicit semantic plan, reducing diversity loss without sacrificing the benefits of instruction tuning.

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