Microsoft Makes Rust a Tier-1 Internal Language and Wires It Into MSVC

Rust is now a tier-1 language inside Microsoft, alongside C++, C# and TypeScript. “Rust now is a Tier One language at Microsoft, and that just means that it sits among C++, C# and TypeScript as the best supported languages for internal development in the company,” Victor Ciura, principal engineer on Microsoft’s Rust tooling team, said in a RustConf keynote in Montreal last week, The Register reported.

In a guest post on the Rust Foundation site, Ciura said tier-1 status gives internal teams “a paved path from local development to production,” covering secure toolchain builds, developer tooling, quality workflows, platform integration and compliance with Microsoft’s Security Development Lifecycle (SDL) requirements.

A Rust backend for the MSVC toolchain

The main technical piece is rustc_codegen_utc, an alternative code generation backend that connects the rustc compiler to UTC, the backend behind MSVC, Microsoft’s native C and C++ compiler for Windows. It sits in the same family as the LLVM, GCC and Cranelift backends.

“Connecting rustc to that backend lets Rust build on the same platform investment, with perfect compatibility out of the box, rather than requiring a parallel implementation of every Windows-specific capability,” Ciura wrote. That brings Windows ABI compatibility, binary hardening, post-link servicing including Hotpatch, and cross-language inlining and optimization to projects that mix Rust and C++.

The backend has been production-ready since early 2026 and self-hosted since Rust 1.90, Ciura said, and more than 100 Microsoft project repositories build with it, with more added each week.

C++ isn’t going anywhere soon

Ciura was clear that “C++ still dominates after decades of development,” and that many systems will use both languages for years. Microsoft already uses Oxidizer, a set of Rust crates for building services, in Microsoft 365 core services such as Outlook, Word, Excel, OneDrive and SharePoint, according to The Register.

Mixing the two languages remains tricky. The Register noted that the Rust compiler can flag memory errors but typically doesn’t cover pointers into C++ memory allocations, a recurring topic at this year’s RustConf. At last year’s conference, Azure CTO Mark Russinovich said about 70% of Windows CVEs are memory safety issues. “No matter how much we really want to make C and C++ better, we can’t make it as good as what Rust starts with,” he said.