Currently using version 6.5.0:

The following prints hi before reportSizes for DTS gets logged:

  await tsup.build({
    entry: files,
    outDir: 'build',
    format: ['cjs', 'esm'],
    sourcemap: true,
    splitting: true,
    dts: true
  });

console.log(`\nProducing \x1b[96m${outfile}\x1b[0m for \x1b[34m@pkmn/${pkg}\x1b[0m...`);

From my actual project:

Presumably this is due to rollup being run in a Worker and the future chain not being propagated appropriately, though from looking at the code myself I didn't see anything obvious