Microsoft Open‑Sources MsQuic: Inside the Cross‑Platform QUIC Library

Microsoft announced on its official technology community blog that it has open‑sourced its internal QUIC library, MsQuic.

QUIC (Quick UDP Internet Connections) is an experimental transport protocol being standardized by the IETF. Originally developed by Google in 2013, QUIC aims to replace HTTPS/HTTP to accelerate web traffic, and HTTP over QUIC (HTTP/3) has been adopted as the next‑generation web standard.

MsQuic is a cross‑platform, general‑purpose library implementing the QUIC protocol, primarily used to support QUIC connections within Microsoft products. It has been optimized for various usage scenarios and is already employed by several Microsoft products and services, including:

Windows, which will ship MsQuic in the kernel and builds its HTTP/3 stack on top of it.

Microsoft 365, which uses HTTP/3 in preview versions of IIS.

.NET Core, where MsQuic underpins HTTP/3 support in Kestrel and HttpClient (available in .NET 5 preview).

SMB in Windows, which uses MsQuic as a prototype.

Microsoft stated that “MsQuic brings performance and security improvements to many important networking scenarios,” noting that its online services benefit most from reduced tail latency and faster connection establishment, and that connections can seamlessly switch networks despite IP address or port changes.

MsQuic is still under development, currently in preview, and is available on both Windows and Linux.