Learning Dynamics in Continual Pre-Training for Large Language Models
Authors: name: Xingjin Wang; name: Howe Tissue; name: Lu Wang; name: Linjing Li; name: Daniel Dajun Zeng
Published: 2025-05-12 17:47:32

Abstract: Continual Pre-Training (CPT) has become a popular and effective method to
apply strong foundation models to specific downstream tasks. In this work, we
explore the learning dynamics throughout the CPT process for large language
models. We specifically focus on how general and downstream domain performance
evolves at each training step, with domain performance measured via validation
losses. We have observed that the CPT loss curve fundamentally characterizes
the transition from one curve to another hidden curve, and could be described
by decoupling the effects of distribution shift and learning rate annealing. We
derive a CPT scaling law that combines the two factors, enabling the prediction
of loss at any (continual) training steps and across learning rate schedules
(LRS) in CPT. Our formulation presents a comprehensive understanding of several
critical factors in CPT, including loss potential, peak learning rate, training
steps, replay ratio, etc. Moreover, our approach can be adapted to customize
training hyper-parameters to different CPT goals such as balancing general and
domain-specific performance. Extensive experiments demonstrate that our scaling
law holds across various CPT datasets and training hyper-parameters.