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abstract indexed · arXiv 2609.17848 · updated 2026-10-18

SFT or RL for Tool-Calling Agents? A Controlled Study Across Data, Method, and Scale

First page of SFT or RL for Tool-Calling Agents? A Controlled Study Across Data, Method, and Scale
From the original paper · arXiv 2609.17848Page 1. Select the image to read the PDF.

This controlled comparison replaces the default assumption that RL post-training (GRPO) or SFT-then-RL pipelines are needed for tool-calling agents, showing simple LoRA SFT is the stronger default and also beats full-parameter fine-tuning. The cost is modest: LoRA SFT runs on a single 24 GB GPU for small-to-mid models, while GRPO adds training complexity, compute, and pipeline overhead for gains that are largely confined to cross-dataset transfer and average under one point. Failure modes include overfitting to the training dataset's tool format when transfer matters, which dataset mixing mitigates, and possible degradation of pretrained agentic behavior if full fine-tuning is used instead of LoRA.

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Why it was shortlisted

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recommendation
adopt
research area
tool use
technical change
LoRA SFT versus GRPO for tool-calling agents
published
2026-09-15

For a constrained-infrastructure team, LoRA SFT is the cheapest method that this controlled study shows wins in-distribution across the full model range, with GRPO justified only as a small-scale experiment when out-of-distribution tool transfer is a production requirement.

About the technical core

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  1. claim 01Paperraft inference
    Read the brief interpretation

    This controlled comparison replaces the default assumption that RL post-training (GRPO) or SFT-then-RL pipelines are needed for tool-calling agents, showing simple LoRA SFT is the stronger default and also beats full-parameter fine-tuning. The cost is modest: LoRA SFT runs on a single 24 GB GPU for small-to-mid models, while GRPO adds training complexity, compute, and pipeline overhead for gains that are largely confined to cross-dataset transfer and average under one point. Failure modes include overfitting to the training dataset's tool format when transfer matters, which dataset mixing mitigates, and possible degradation of pretrained agentic behavior if full fine-tuning is used instead of LoRA.

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  2. claim 02Paperraft inference

    SFT with LoRA is the strongest in-distribution method in 15 of 18 settings across Qwen3 0.6B-32B; GRPO wins 29 of 54 cross-dataset transfer settings but by under one point on average, and LoRA outperforms full-parameter fine-tuning by better preserving pretrained agentic behavior.

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quality

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compute and memory

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latency

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operations

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software compatibility

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data and training

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Provisional research brief updated 2026-10-18. Paperraft has not reproduced this experiment.

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