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Microsoft Names Rust a Tier-1 Internal Language, Details New MSVC-Compatible Compiler Backend

Microsoft has elevated Rust to Tier-1 status alongside C++, C#, and TypeScript, and detailed a new compiler backend linking Rust to MSVC.

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Editor's Note ·

Correction:
This article quoted The Register as saying the Copilot technology stack "also leverages Rust substantially." The Register's actual wording is: "The Copilot tech stack also owes quite a bit to Rust." The underlying fact (Copilot uses Rust) is accurate; the quoted phrasing was not verbatim.
Correction:
This article quoted The Register as saying the Rust compiler "cannot always track memory safety across language boundaries involving C++ pointers." The Register's actual wording is: "While the Rust compiler can flag memory errors, it typically doesn't cover pointers into the C++ memory allocations." The underlying point (a Rust/C++ interop memory-safety gap) is accurate; the quoted phrasing was not verbatim.

Overview

Microsoft has elevated Rust to “Tier One” status alongside C++, C#, and TypeScript for internal development, according to The Register. Victor Ciura, a principal engineer on Microsoft’s Rust tooling team, announced the change at RustConf in Montréal, and separately detailed the underlying engineering work in a guest post on the Rust Foundation’s site: “Today, Rust sits among C++, C#, and TypeScript as one of the best-supported languages for internal development at Microsoft.”

What We Know

  • Rust now has the same “Tier-1 language” engineering status inside Microsoft as C++, C#, and TypeScript, according to both The Register and the Rust Foundation.
  • Ciura wrote that the designation “means giving internal teams a paved path from local development to production: secure toolchain builds, productive developer tooling, quality workflows, deep platform integration, and compliance with the SDL requirements Microsoft software must meet,” according to the Rust Foundation.
  • Rust already appears in more than 100 Microsoft project repositories, a figure confirmed independently by both The Register and the Rust Foundation, which added that “this rollout continues each week as more repositories adopt it.”
  • Microsoft built Oxidizer, described as a collection of tools for building scalable services in Rust, which powers core Microsoft 365 services including Outlook, Word, Excel, OneDrive, and SharePoint; the Copilot technology stack “also leverages Rust substantially,” according to The Register.
  • Microsoft has built rustc_codegen_utc, a compiler backend that connects the Rust compiler, rustc, directly to Microsoft Visual C++‘s (MSVC) internal toolchain for Windows. Ciura describes it as sitting “in the same architectural family as rustc_codegen_llvm, rustc_codegen_gcc and rustc_codegen_cranelift,” plugging into “the same backend interface” to connect “rustc’s shared compiler machinery to the MSVC backend (aka ‘UTC’),” according to the Rust Foundation.
  • Ciura said rustc_codegen_utc “has been production-ready since early 2026” and “has been self-hosted since Rust 1.90,” according to the Rust Foundation. The Register reported that the backend creates “a unified code generation platform for Rust and C++ on Windows” while maintaining compatibility without requiring parallel implementations of Windows-specific capabilities.
  • Azure CTO Mark Russinovich said approximately 70 percent of Windows CVEs stem from memory issues, adding: “One of the things that I realized a long time ago is that 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,” according to The Register.
  • Interoperability between Rust and existing C++ code remains a challenge: the Rust compiler “cannot always track memory safety across language boundaries involving C++ pointers,” according to The Register. Ciura pointed to the Rust Foundation’s Interoperability Initiative as an ongoing effort addressing the broader problem space, according to the Rust Foundation.

What We Don’t Know

Neither source specifies how many Microsoft engineers currently work on Rust tooling internally, nor a target date for expanding rustc_codegen_utc coverage beyond the current set of repositories. It’s also not stated how the 70 percent memory-safety CVE figure was calculated or over what time period it applies.

Background

Rust is a systems programming language designed to prevent memory-safety bugs — such as buffer overflows and use-after-free errors — that are common in C and C++ code, without requiring a garbage collector. Microsoft Visual C++ (MSVC) is Microsoft’s native compiler toolchain for building Windows software. rustc_codegen_utc plugs Rust’s compiler into that same MSVC backend rather than requiring a separate, parallel implementation of Windows-specific compiler features for Rust code.