ExecuTorch is PyTorch's unified solution for deploying AI models on-device (mobile, embedded, edge). It enables direct export from PyTorch without intermediate format conversions (.onnx, .tflite) and powers Meta's production on-device AI across Instagram, WhatsApp, Quest 3, and Ray-Ban Meta Smart Glasses. The framework provides an ahead-of-time (AOT) compilation workflow: Export → Compile → Execute, supporting LLMs (Llama 3.2/3.1/3, Qwen 3, Phi-4-mini), vision (MobileNetV2, DeepLabV3, YOLO26), speech (Whisper), and multimodal models (Llava, Voxtral) across 12+ hardware backends including XNNPACK, CoreML, Qualcomm QNN, MediaTek Neuropilot, ARM Ethos-U, NXP, Cadence DSP, Vulkan, CUDA (experimental), Metal (experimental), and MLX (experimental). The architecture is modular with core runtime (C++/C), export pipeline (Python), backend-specific delegates, and examples/tools for model conversion and benchmarking. Key entry points include the Python API (torch.export.export() → to_edge_transform_and_lower() → .to_executorch()), C++ API (executorch::runtime::Module), backend partitioners (XnnpackPartitioner, CoreMLPartitioner), and command-line tools for model export and benchmarking. Data flows involve model export to Edge IR (EXIR), partitioning/lowering for backend, serialization to .pte, and runtime execution via delegate interfaces. External dependencies include PyTorch, FlatBuffers, backend-specific SDKs (QNN, Ethos-U, CoreML/Metal, Vulkan, WebGPU), CMake, Buck2, and testing frameworks. The codebase demonstrates strong engineering practices with reusable components like the visitor pattern for operator lowering, quantization pipelines for LLMs, memory planning utilities, and a flexible delegate framework. While actively maintained with frequent commits and CI/CD, technical drift is medium due to experimental backends, generated code synchronization challenges, and conditional build complexity across numerous hardware targets.