PortLLM

Theoretical and empirical analysis of long-term temporal portability of LoRA patches across continual pretraining updates

This arXiv paper investigates PortLLM, a training-free and data-free scheme for adapting LLMs after continual pretraining, extending prior short-term results to 10 continual pretraining steps across Mistral, Gemma, and Qwen base models. The authors find that LoRA patches remain portable across longer update horizons, suggesting repeated fine-tuning is unnecessary when base models are periodically updated. Two theoretical analyses are offered, identifying near-orthogonality of high-dimensional vectors as the geometric mechanism underlying temporal portability. The work has practical implications for reducing fine-tuning overhead in production deployments with frequently updated base models.