Do Gaussian Scenes Contain Enough Structure for Intrinsic Segmentation?

Gaussian segmentation is usually posed as transferring object knowledge from 2D foundation models into a 3D representation. This leaves a fundamental question unanswered: how much object structure is already encoded by a trained gaussian scene? We investigate this question with GS-IntSeg, an intrinsic, mask-free, and training-free method that constructs partitions using only: gaussian geometry, opacity, spherical-harmonic radiance, and deformation trajectories. On the dynamic Neu3D and HyperNeRF datasets, GS-IntSeg obtains a mean of 0.677 mIoU across multi-view and monocular scenes without masks, external features, or segmentation training. This intrinsic formulation also enables GS-IntSeg to require approximately 2.5 minutes per HyperNeRF scene on a consumer RTX 5080 to construct its partitions, over 10x faster than SAM-based methods that require mask generation, feature rendering, and other stages. These results suggest that gaussians alone can approach mask-supervised performance in gaussian scenes segmentation. While a gap remains between intrinsic and foundation model based methods, to our knowledge, GS-IntSeg is the first mask-free approach to gaussian segmentation, motivating a re-evaluation of the assumption that gaussian scene segmentation must be based on external masks and pointing toward an alternative faster, more generalizable segmentation approach.