Modal has rebuilt the filesystem path used by its VM Sandboxes to work at the block level instead of translating every guest operation into a remote file request. The change targets agent workloads that repeatedly create processes, inspect repositories and modify many small files, where filesystem latency can become a bottleneck.
The company’s earlier ImageFS design helped containers start quickly by loading data lazily. Virtual machines add another boundary: the guest operating system expects a block device, while a file-oriented bridge can generate many round trips and metadata operations. Modal’s newer approach exposes storage in the form the guest filesystem already expects, reducing translation work between the virtual machine and the underlying image service.
The design also supports copy-on-write behavior, so a sandbox can begin from a shared image and record only its changes. That is useful for short-lived coding agents because each run can receive an isolated writable environment without duplicating an entire base image first.
Modal presents the redesign as infrastructure for its recently released VM Sandboxes, not as a standalone filesystem product. Real-world gains will depend on workload patterns, especially whether a task is dominated by small file operations, image loading, computation or network calls.