S-Agent: Spatial Tool-Use Makes an 8B Agent Rival GPT-5.4 on Spatial Reasoning: Spatio-Temporal Evidence Accumulation

1Key Takeaways

• What: S-Agent is an agent framework for spatial reasoning over multi-view images and video, where a vision-language model acts as a planner that directs a hierarchy of spatial tools to build one shared 3-D model of the scene — what the paper calls spatio-temporal evidence accumulation .
• Why: Spatial questions — how far apart, how many, which way is it facing — need geometry that no single flat frame carries .
• Moving that geometry out of the model's head and into an explicit 3-D store lets an….