DeepEP is a high-performance communication library developed by DeepSeek for distributed Mixture-of-Experts (MoE) model training and inference. Its primary function is implementing expert-parallel (EP) all-to-all dispatch and combine operations, routing tokens to the correct GPU holding an expert and gathering the results. It also provides general collective communication primitives (all-reduce, reduce-scatter, all-gather) optimized for multi-node multi-GPU clusters with NVLink and RDMA interconnects. The architecture is a hybrid Python/C++/CUDA library. The Python layer (deep_ep) provides user-facing buffer classes (EPBuffer, BucketBuffer, EngramBuffer, PPBuffer) and orchestration utilities. The C++/CUDA layer (csrc/, deep_ep/include/) contains JIT-compiled kernels that leverage cutting-edge NVIDIA Hopper/Blackwell features (TMA, mbarriers, NCCL GIN) for maximum performance. The library is designed to overlap communication with computation through deferred epilogue patterns. The codebase exhibits exceptional craftsmanship in its low-level CUDA kernels, particularly the ptx.cuh utility layer and the distributed barrier implementations. The Python utilities (EventOverlap, weak_lru, EnvOverride, BufferAllocator) are well-isolated, elegant patterns that are genuinely reusable in other GPU or distributed computing projects. However, the library has a high technical drift risk due to its deep reliance on experimental and rapidly evolving NVIDIA APIs (NCCL device-side, specific CUDA architecture features). It is tightly coupled to a specific hardware stack (Hopper+ GPUs, NVLink, RDMA) and software versions (CUDA 13.1+, NCCL 2.32.3+). While actively maintained, its specialized nature and complex build system limit its applicability outside of large-scale MoE training on cutting-edge NVIDIA clusters.