I'm not sure I'm seeing the same pattern for this particular version. Comparing the minified versions I see the file size delta for version 15.4.0-rc3 is -4.32

I'm not sure I'm seeing the same pattern for this particular version. Comparing the minified versions I see the file size delta for version 15.4.0-rc3 is -4.32 KB, meaning a reduction in file size. For reference: Total minified size is now at 145.2 KB for React + DOM versus 149.52 KB in 15.3.2. That's a -2.89% reduction.