SparseWorldMed: Learned Sparse Attention for Efficient Long-Horizon Clinical Episode World Models
We present SparseWorldMed, a clinical episode world model that replaces O(N²) full attention with data-dependent TopK sparse attention (O(NK)). Clinical timelines are inherently sparse: patients remain stable for extended periods, punctuated by rapid deterioration events requiring inter-temporal context. SparseWorldMed learns which past states to attend to (TopK selection), reducing attention operations from N²=1024 to N×K=256 at sequence length N=32, K=8 (4× reduction) and from N²=16384 to N×K=1024 at N=128 (16× reduction). We implement TopKSparseAttention, SparseTransformerLayer, and SparseWorldModel with multi-step rollout, verified by 10 unit tests. The sparse world model integrates directly as a drop-in replacement for MedOS's ClinicalWorldModel, enabling long-horizon clinical episode simulation.