Mono-InternVL-1.5: Towards Cheaper and Faster Monolithic Multimodal
  Large Language Models
Authors: name: Gen Luo; name: Wenhan Dou; name: Wenhao Li; name: Zhaokai Wang; name: Xue Yang; name: Changyao Tian; name: Hao Li; name: Weiyun Wang; name: Wenhai Wang; name: Xizhou Zhu; name: Yu Qiao; name: Jifeng Dai
Published: 2025-07-16 18:31:23

Abstract: This paper focuses on monolithic Multimodal Large Language Models (MLLMs),
which integrate visual encoding and language decoding into a single model.
Existing structures and pre-training strategies for monolithic MLLMs often
suffer from unstable optimization and catastrophic forgetting. To address these
challenges, our key idea is to embed a new visual parameter space into a
pre-trained LLM, enabling stable learning of visual knowledge from noisy data
via delta tuning. Based on this principle, we first introduce Mono-InternVL, an
advanced monolithic MLLM that incorporates a set of visual experts through a
multimodal mixture-of-experts architecture. In addition, we design an
innovative Endogenous Visual Pre-training (EViP) for Mono-InternVL to maximize
its visual capabilities via progressive learning. Mono-InternVL achieves
competitive performance against existing MLLMs but also leads to relatively
expensive data cost. Therefore, we further present Mono-InternVL-1.5, a cheaper
and stronger monolithic MLLM equipped with an improved EViP (EViP++). EViP++
introduces additional visual attention experts to Mono-InternVL-1.5 and
re-organizes the pre-training process in an efficient manner. During inference,
it includes a fused CUDA kernel to speed up its MoE operations. With these
designs, Mono-InternVL-1.5 significantly reduces training and inference costs,
while still maintaining competitive performance with Mono-InternVL. To evaluate
our approach, we conduct extensive experiments across 15 benchmarks. Results
demonstrate that Mono-InternVL outperforms existing monolithic MLLMs on 12 out
of 15 benchmarks, e.g., +114-point improvement over Emu3 on OCRBench. Compared
to its modular counterpart, i.e., InternVL-1.5, Mono-InternVL-1.5 achieves
similar multimodal performance while reducing first-token latency by up to 69%.
Code and models are released at https://github.com/OpenGVLab/Mono-InternVL.