Vercel Sandbox starts up to 4x faster

Vercel sped up Sandbox startup: outside the Washington, D.C. (iad1) region, sandboxes now initialize up to 4x faster when the image data they need is already in a regional cache.

Before, initialization went back to origin image storage in iad1. On a cache hit, it now reads the cached data close to where the sandbox runs. The caching covers managed images and custom images backed by Vercel Container Registry, plus snapshots based on those images.

In Vercel's internal end-to-end benchmarks with Vercel Managed Images, startup time dropped about 75% in Paris and from about 3.5s to 1.05s in Seoul. Regions closer to iad1 should see smaller gains, since their requests already travel a shorter distance. These are Vercel's own numbers, and the speedup only applies when the image data is a cache hit.