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논문 기본 정보

저자정보
(Soongsil University) (Soongsil University)
저널정보
국제인공지능학회 The International Journal of Internet, Broadcasting and Communication The International Journal of Internet, Broadcasting and Communication Vol.18 No.5
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    초록·키워드

    Foundation models are commonly fine-tuned to improve performance on specific downstream tasks. However, task-specific adaptation can degrade performance on non-target tasks, a phenomenon known as forgetting that undermines the broad generalization capabilities of foundation models. Prior studies on large language models have reported less forgetting under reinforcement fine-tuning (RFT) than under supervised fine-tuning (SFT), but the underlying mechanism remains unresolved. Isolating this mechanism is difficult in language-model reasoning tasks because multiple valid solution trajectories may yield the same final answer. By contrast, each time-series context window is paired with a single observed future trajectory, providing a more controlled setting for comparing the two paradigms. We therefore compare SFT with RFT instantiated using Group Relative Policy Optimization in two time series foundation models, Chronos-T5 and Moirai, using a systematically controlled family of loss configurations. At matched levels of target-task improvement, RFT exhibited significantly less forgetting than SFT in three of ten evaluable backbone–target cells, whereas SFT exhibited less forgetting in one cell; the remaining six comparisons were statistically inconclusive. We then decomposed the RFT objective by removing individual components from RFT and adding corresponding components to SFT. Among eight cells in which SFT produced at least 2% forgetting, seven showed a consistent separation based on whether the positive optimization target was model-generated or externally observed, rather than on the presence of any individual loss component. Furthermore, freezing model- generated targets after an initial adaptation phase showed no detectable reduction in retention relative to resampling them at every training step. These results indicate that the choice of optimization target plays a central role in forgetting during TSFM fine-tuning.

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