STAC: Plug-and-Play Spatio-Temporal Aware Cache Compression for Streaming 3D Reconstruction

Online 3D reconstruction from streaming inputs requires both long-term temporal consistency and efficient memory usage. While causal VGGT transformers address this challenge through key-value (KV) cache mechanism, the linear growth of the cache introduces a significant memory bottleneck. When memory constraints trigger early eviction, reconstruction quality and temporal consistency deteriorate markedly. In this work, we observe that attention patterns in causal transformers for 3D reconstruction exhibit intrinsic spatio-temporal sparsity. Leveraging this insight, we propose **STAC**, a *S*patio-**T**emporally **A**ware **C**ache compression framework specifically designed for streaming 3D reconstruction using large causal transformers. STAC incorporates three key components: a **Working Temporal Token Caching** mechanism that preserves long-term informative tokens based on decayed cumulative attention scores; a **Long-term Spatial Token Caching** scheme that consolidates spatially redundant tokens into voxel-aligned representations for memory-efficient storage; and a **Chunk-based Multi-frame Optimization** strategy that jointly optimizes consecutive frames to enhance temporal coherence and leverage GPU parallelism. Extensive experiments demonstrate that **STAC** achieves state-of-the-art reconstruction quality while reducing memory consumption by 8.5$\times$ and accelerating inference by a factor of 3.5$\times$, enabling scalable and real-time 3D reconstruction in streaming settings. The code will be made publicly available upon acceptance.