Hey, thanks for the report.
This is a known issue caused by Windows process startup overhead for hooks. Even minimal hooks can be noticeably slower on Windows than on macOS. The team is already working on improving hook performance on Windows.
See also: Similar report for the beforeTabFileRead hook
Since beforeSubmitPrompt runs less often than tab-related hooks, the impact should be lower, but the overhead is still noticeable. We’ll track this alongside the existing Windows hook performance improvements.