# Vitest v4.0.4 — Release & Upgrade Intelligence
- **Product:** Vitest (https://vitest.dev)
- **Version:** v4.0.4
- **Released:** Oct 27, 2025
- **Impact Score:** 5/10
- **Breaking Changes:** Not verified
- **Canonical Analysis:** https://changelogs.us/vitest/updates/v4.0.4/

## Executive Summary (TL;DR)
Vitest v4.0.4. Source highlight:    🐞 Bug Fixes

## Improvements
- **utils**: Optimized reducer to avoid creating new objects &nbsp;-&nbsp; by @Connormiha in https://github.com/vitest-dev/vitest/issues/8818 <samp>(d19ce)</samp>

## Bug Fixes
- Correct typo &nbsp;-&nbsp; by @benmccann in https://github.com/vitest-dev/vitest/issues/8796 <samp>(ede1f)</samp>
- Publish a missing context file for webdriverio &nbsp;-&nbsp; by @sheremet-va in https://github.com/vitest-dev/vitest/issues/8824 <samp>(7c7b6)</samp>
- Support mocking builtins without `node:` prefix &nbsp;-&nbsp; by @sheremet-va in https://github.com/vitest-dev/vitest/issues/8829 <samp>(06208)</samp>
- Runner's error listener causing `MaxListenersExceededWarning` &nbsp;-&nbsp; by @AriPerkkio in https://github.com/vitest-dev/vitest/issues/8820 <samp>(d1bff)</samp>
- Capture workers `stdio` to logger &nbsp;-&nbsp; by @AriPerkkio in https://github.com/vitest-dev/vitest/issues/8809 <samp>(fb95f)</samp>
- Allow classes in `vi.mocked` utility &nbsp;-&nbsp; by @sheremet-va in https://github.com/vitest-dev/vitest/issues/8839 <samp>(f8756)</samp>