Evaluating a feature flag should not begin with an avoidable network wait. Vercel’s October 29 SDK update changes how Vercel Flags initializes on cold starts and how it reports usage after a response.
The SDK now loads the flag datafile bundled with the deployment when the client is created. Each function invocation includes the current datafile revision, allowing the SDK to check freshness without a separate network request.
Two changes, two different measurements
Vercel reports that internal testing reduced p75 cold-start SDK initialization from more than 70 milliseconds to 10 milliseconds, roughly seven times faster. That measures SDK initialization in Vercel’s tests, rather than the complete response time of every application using flags.
Usage reporting also moves from waitUntil to the Vercel runtime. According to the announcement, reporting no longer keeps a function running after the response or adds to its duration. This is separate from the time a visitor waits for the page.
The change requires @flags-sdk/vercel version 1.5.3 or later and a new deployment. For an existing application, compare cold-start behavior and reported function duration after the update, while checking that flag evaluations still return the expected values. The release concerns the Vercel adapter, rather than every flag provider.
Source
Vercel — Flags initialization and usage reporting, October 29
