Vercel Flags starts 7x faster and no longer extends function duration

The Vercel Flags SDK now loads and parses the bundled flags datafile immediately upon client creation, ensuring flags are ready before any application code evaluates them. This eliminates the prior delay caused by waiting for the datafile to be read during the first flag evaluation. The change shifts initialization from a post-client-creation step to a pre-evaluation phase, reducing the time required before flags can be used in the application.

Every function invocation now includes the current datafile revision, allowing the SDK to verify if the bundled datafile is up to date without making a network request. This removes the need for an additional HTTP call to check for updates, which previously contributed to latency. The revision check is performed locally using the embedded datafile, streamlining the process and reducing overhead during both cold and warm starts.

Internal testing showed that removing the network wait for datafile updates reduced the p75 cold-start SDK initialization time from over 70 milliseconds to 10 milliseconds, representing approximately a sevenfold improvement. After initialization, flag reads occur instantly, as the datafile is already loaded and parsed in memory. This acceleration applies uniformly across all deployment environments where the SDK is used.

Usage reporting no longer relies on the waitUntil mechanism, which previously kept functions running after the response was sent to collect analytics. The SDK now passes usage events directly to the Vercel runtime, ensuring that reporting does not extend function duration. This change removes a source of latency and simplifies the lifecycle of function execution by decoupling analytics from the response handling process.