Rust 1.49: What's New, Release History & Support Lifecycle

What Is New in Rust 1.49

How does Rust 1.49 improve support for ARM platforms?

Rust 1.49 promotes the aarch64-unknown-linux-gnu target to Tier 1, giving it the same testing guarantees as x86 platforms.

• Tier 1 means the full test suite runs on every change and pre-built binaries are shipped.
• The aarch64-apple-darwin (Apple M1) and aarch64-pc-windows-msvc (Windows ARM) targets reach Tier 2, providing ready-to-install binaries via rustup while the test suite is not yet executed on those platforms.
• This matters if your CI or production workloads run on 64-bit ARM; you can now depend on official binaries and expect higher stability.

What changes were made to the built-in test framework in Rust 1.49?

The test runner now captures all output from spawned threads and only displays it when a test fails.

#[test]
fn thready_pass() {
    println!("fee");
    std::thread::spawn(|| {
        println!("fie");
        println!("foe");
    })
    .join()
    .unwrap();
    println!("fum");
}

Running this test with Rust 1.48 prints the thread's println! lines interleaved with the harness output. With Rust 1.49 the output is hidden on success, producing a clean "ok" line; on failure the full stdout (including fee, fie, foe, fum) is shown, aiding debugging.

Which new stable library functions arrived in Rust 1.49?

Rust 1.49 adds three new stable functions to the standard library and promotes two existing functions to const, allowing them in constant contexts.

• The exact function signatures are listed in the detailed release notes; they expand the API surface for low-level and const-eval use cases.
• Making functions const enables compile-time computation, which can reduce runtime overhead in performance-critical code.

How does Tier 1 support affect CI pipelines for aarch64-unknown-linux-gnu?

CI pipelines can now pull pre-built aarch64-unknown-linux-gnu binaries from the official channel and rely on the fact that the full Rust test suite runs on that platform for every change.

• This reduces the need for custom cross-compilation steps.
• It also gives higher confidence that platform-specific bugs are caught upstream.