Function uploads are now skipped when code hasn't changed, reducing build times by 400-600ms on average and up to 5 seconds for larger builds.
Previously, deployment-specific environment variables like VERCEL_DEPLOYMENT_ID were included in the function payload, making every deployment unique even with identical code. These variables are now injected at runtime, allowing Vercel to recognize unchanged functions and skip redundant uploads.
This optimization applies to Vercel Functions without a framework, and projects using Python, Go, Ruby, and Rust. Next.js projects will receive the same improvement soon.
The optimization is applied automatically to all deployments with no configuration required.