Inside Modal Notebooks: How Modal Built a Cloud GPU Notebook That Boots in Seconds

Modal detailed the engineering behind Modal Notebooks, its cloud Jupyter notebook that boots GPUs and custom images in seconds with real-time collaboration. Kernels run inside Modal Sandboxes, with a modal-kernelshim daemon translating Jupyter ZeroMQ messages into HTTP calls tunneled through Modal's control plane. A lazy-loading Rust FUSE container filesystem fetches file contents on demand through a tiered cache, avoiding the image-unpacking latency that can approach a minute for an 8 GB Python/ML image.