FuseChat: Knowledge Fusion of Chat Models
Authors: name: Fanqi Wan, name: Ziyi Yang, name: Longguang Zhong, name: Xiaojun Quan, name: Xinting Huang, name: Wei Bi

While training large language models (LLMs) from scratch can indeed lead to
models with distinct capabilities and strengths, this approach incurs
substantial costs and may lead to potential redundancy in competencies. An
alternative strategy is to combine existing LLMs into a more robust LLM,
thereby diminishing the necessity for expensive pre-training. However, due to
the diverse architectures of LLMs, direct parameter blending proves to be
unfeasible. Recently, FuseLLM introduced the concept of knowledge
fusion to transfer the collective knowledge of multiple structurally varied
LLMs into a target LLM through lightweight continual training. In this report,
we extend the scalability and flexibility of the FuseLLM framework to
realize the fusion of chat LLMs, resulting in FuseChat.
FuseChat comprises two main stages. Firstly, we undertake knowledge
fusion for structurally and scale-varied source LLMs to derive multiple target
LLMs of identical structure and size via lightweight fine-tuning. Then, these
target LLMs are merged within the parameter space, wherein we propose a novel
method for determining the merging weights based on the variation ratio of
parameter matrices before and after fine-tuning. We validate our approach using
three prominent chat LLMs with diverse architectures and scales, namely
NH2-Mixtral-8x7B, NH2-Solar-10.7B, and
OpenChat-3.5-7B. Experimental results spanning various chat domains
demonstrate the superiority of \textsc{FuseChat-7B} across a broad
spectrum of chat LLMs at 7B and 34B scales, even surpassing GPT-3.5
(March) and approaching Mixtral-8x7B-Instruct. Our code, model
weights, and data are openly accessible at
https://github.com/fanqiwan/FuseLLM.