Liu, Aiwei, Shi, Cheng, Wu, Chuhan, Lei, Ci, Lu, Di, He, Donald, Zhang, Fan, Kong, Fanhao, Zhang, Feifei, Wang, Guan, Wang, Haicheng, Liu, Haoyu, Yu, Houjin, Ding, Jiachen, Feng, Jiayi, Zhou, Jie, Chi, Jijun, Shi, Jindi, Lei, Jing, Zhang, Junjie, Li, Laiyi, Tian, Le, Zhang, Linhao, Fan, Miao, Zhang, Sijun, Jia, Wei, Shi, Weiwei, Li, Wenhan, Zhao, Wentao, Liang, Wenteng, Zhou, Xiao, Zhou, Xiaojin, Wang, Xihuai, Gao, Xinyu, Wang, Xuanliang, Ao, Xuyang, Yu, Yang, You, Yangxiu, Zhao, Yinuo, Kuang, Yufei, Wang, Yufei, Liu, Yuan, Liu, Yuan, Chen, Yuwen, Tian, Zhencong, Zhao, Zhongyin, Yu, Zilin, Wang, Zitao
Abstract
Scaling Large Language Models (LLMs) has been driven mainly by enlarging the Transformer backbone, but for an already-strong model this requires another round of costly pretraining. We study whether an existing backbone can keep improving by allocating more computation to each token while leaving the Transformer backbone fixed. Depth-recurrent (looped) Transformers pursue this goal but are hard to scale, because looped computation does not fit naturally with the pipeline parallelism used to train the largest models. We add computation along the sequence-length dimension, where the extra computation is simply a longer input and stays compatible with standard large-model training. We propose Hidden Decoding, a sequence-length scaling method applied during continued pretraining (CPT). It expands each token into n streams with independent embedding tables and keeps the intermediate streams' key-value cache as context, so each token performs more internal computation without adding or widening Transformer layers. To keep this affordable at scale, we introduce Stream-Factorized Attention, in which most layers attend only within each stream and only a few layers mix across streams, reducing the attention cost from quadratic to roughly linear in n. Experiments support two scaling results. At frontier scale, we train WeLM-HD4-80B and WeLM-HD4-617B at n=4 and improve their matched non-HD baselines, making Hidden Decoding the first demonstrated sequence-length scaling method at the 100B+ MoE scale. Across expansion factors, the gains grow as n increases, showing that sequence-length expansion is a practical fixed-backbone scaling path for frontier-scale LLMs.
Chinese Translation
大型语言模型(LLMs)的扩展主要是通过扩大Transformer主干实现的,但对于已经强大的模型,这需要进行另一轮昂贵的预训练。我们研究了是否可以通过为每个标记分配更多计算资源来持续改进现有的主干,同时保持Transformer主干不变。深度递归(循环)Transformer追求这一目标,但由于循环计算与用于训练最大模型的流水线并行性不自然契合,因此难以扩展。我们在序列长度维度上增加计算,其中额外的计算仅仅是更长的输入,并保持与标准大模型训练的兼容性。我们提出了隐式解码(Hidden Decoding),这是一种在持续预训练(CPT)期间应用的序列长度扩展方法。它将每个标记扩展为n个流,并使用独立的嵌入表,同时将中间流的键值缓存作为上下文,从而使每个标记在不增加或扩展Transformer层的情况下执行更多内部计算。为了在大规模下保持这一方法的可承受性,我们引入了流因子化注意力(Stream-Factorized Attention),其中大多数层仅在每个流内进行注意力计算,只有少数层跨流混合,从而将注意力成本从二次降低到大约线性与n的关系。实验支持了两个扩展结果。在前沿规模下,我们训练了WeLM-HD4-80B和WeLM-HD4-617B,n=4,并改善了它们的匹配非HD基线,使隐式解码成为在100B+ MoE规模下首次展示的序列长度扩展方法。在扩展因子之间,随着n的增加,收益不断增长,表明序列长度扩展是前沿规模LLMs的一个实用固定主干扩展路径。