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arXiv · 2610.28407

The Instruction Tax on Factual Recall: Base Models Can Beat Their Instruction-Tuned Counterparts

Christophe Khalil·Aya Mourad
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Abstract

We present our solution to the AKBC LM-KBC 2026 Shared Task, where we achieved a score of 0.6836 on the official leaderboard, more than double the baseline of 0.2964. This task requires generating all possible objects for subject-relation pairs using a language model with up to 32 billion parameters, with no retrieval or fine-tuning involved. We show that the prompting methodology is as important as the model architecture: while the instruction-tuned model version achieves 0.5681 with its chat interface, the base model achieves 0.6836 when prompted using text completion. Thus, instruction tuning decreases factual recall; we refer to this effect as the instruction tax, which is caused by the model's weights rather than the prompting method. Our final solution is fairly straightforward: we prompt the base model with some examples from the training data, generate 64--256 outputs, and retain only the repeated ones. Two specialized methods are then applied for each relation: one improves the recall of large answer sets, and the other verifies a person's vitality before predicting their place of death.

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Christophe Khalil, Aya Mourad. 2026-10-20. The Instruction Tax on Factual Recall: Base Models Can Beat Their Instruction-Tuned Counterparts. https://arxiv.org/abs/2610.28407

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