Omni-R1: Reinforcement Learning for Omnimodal Reasoning via Two-System
  Collaboration
Authors: name: Hao Zhong, name: Muzhi Zhu, name: Zongze Du, name: Zheng Huang, name: Canyu Zhao, name: Mingyu Liu, name: Wen Wang, name: Hao Chen, name: Chunhua Shen

Long-horizon video-audio reasoning and fine-grained pixel understanding
impose conflicting requirements on omnimodal models: dense temporal coverage
demands many low-resolution frames, whereas precise grounding calls for
high-resolution inputs. We tackle this trade-off with a two-system
architecture: a Global Reasoning System selects informative keyframes and
rewrites the task at low spatial cost, while a Detail Understanding System
performs pixel-level grounding on the selected high-resolution snippets.
Because ``optimal'' keyframe selection and reformulation are ambiguous and hard
to supervise, we formulate them as a reinforcement learning (RL) problem and
present Omni-R1, an end-to-end RL framework built on Group Relative Policy
Optimization. Omni-R1 trains the Global Reasoning System through hierarchical
rewards obtained via online collaboration with the Detail Understanding System,
requiring only one epoch of RL on small task splits.
  Experiments on two challenging benchmarks, namely Referring Audio-Visual
Segmentation (RefAVS) and Reasoning Video Object Segmentation (REVOS), show
that Omni-R1 not only surpasses strong supervised baselines but also
outperforms specialized state-of-the-art models, while substantially improving
out-of-domain generalization and mitigating multimodal hallucination. Our
results demonstrate the first successful application of RL to large-scale
omnimodal reasoning and highlight a scalable path toward universally foundation
models.