Software

ReactOS Rebase Cuts API Failures, Boosts NT6 Support

ReactOS Rebase MSVCRT to Wine 10 — 30% Fewer Failures
NT6 Compatibility
  • Key Takeaways:
  • ReactOS synced its MSVCRT implementation with Wine 10.0, marking a major step toward Windows NT6 (NT 6.0) compatibility.
  • The rebase reduced API test failures by about 29.6% (roughly 7,574 of 25,517 failures).
  • Work is tracked in ReactOS GitHub merge request #8204 and was reported by Phoronix.
  • The change improves application compatibility and accelerates NT6 bring-up work for 2026.

What changed

ReactOS developers imported the MSVCRT (Microsoft C Runtime) implementation from Wine 10.0 into the ReactOS codebase. MSVCRT is a core DLL used by many Windows applications, so its behavior strongly influences compatibility.

Why the rebase matters

By aligning MSVCRT with Wine 10.0, ReactOS inherits years of compatibility fixes and behavioral refinements that Wine has accumulated. Those improvements translate to fewer API mismatches and more applications running as expected on ReactOS.

Rebase details and tracking

The rebase was prepared over several months and is documented in the projects merge request on GitHub: https://github.com/reactos/reactos/pull/8204. ReactOS also announced the change on X (Twitter): https://x.com/reactos/status/2006126591907160377.

Test results and impact

ReactOS reports that the MSVCRT import fixes "(roughly) 7574 out of 25517 test failures, i.e. 29.6% of all failures." That ~30% reduction in API test failures is a measurable improvement for an OS focused on reproducing Windows behaviors.

What users and developers should expect

Users may see better compatibility with applications that rely on the C runtime, while developers should find fewer false negatives in automated API tests. The changes dont make ReactOS fully NT6-compatible, but they remove a substantial class of regressions.

Why Windows NT6 compatibility matters

Windows NT6 marks the Vista/Server 2008 generation and later API surface that many modern applications target. Advancing NT6 compatibility broadens the range of software that can be supported by ReactOS without modification.

What to watch in 2026

ReactOS turns a milestone year and the MSVCRT rebase sets a practical direction for the projects NT6 bring-up. Expect more targeted rebases, driver and subsystem work, and continued test-suite reporting as the team narrows compatibility gaps.

Coverage of this update appeared on Phoronix (Michael Larabel). Follow the ReactOS project on GitHub and its social channels for detailed progress and future merge requests.

Read more