TL;DR
Rust 1.100.0 was announced on Nov. 12, 2026, with the never type and core parts of the allocator API among its headline stable features. The release also adds DropGuard and changes to Cargo; older-edition projects may encounter compatibility effects from the never-type fallback change.
The Rust team announced Rust 1.100.0 on Nov. 12, bringing the never type and core parts of the allocator API into stable Rust, alongside a new DropGuard utility and several Cargo changes. The release matters to developers because some additions affect type checking and resource handling, while the never-type change also alters compiler behavior for projects using Rust editions 2015, 2018 and 2021.
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The release announcement says the never type, written !, is now stable after a decade of work and five unsuccessful stabilization attempts. It represents computations that do not return a value, such as a function that exits or a branch that returns early. Rust already allowed some uses of the type; 1.100 permits developers to name it in more places, including as a type parameter such as Result
That change comes with a compatibility consequence: for editions before 2024, the compiler’s never-type fallback changes from () to !. The team says the effect should be limited in most code, but some uncommon patterns may behave differently, including cases involving ignored results from functions with generic return types. The change may also lead the compiler to identify more code as unreachable. The release notes say future-compatibility warnings were issued in advance and fixes were released for affected public crates.
Rust 1.100 also stabilizes the core of allocator_api, including the Allocator trait. The release says custom allocators can be used with certain standard-library types, currently Vec and Box. Another standard-library addition, core::mem::DropGuard, runs a supplied closure when its guard is dropped and can be dismissed to return the guarded value without running that closure. The release lists further Cargo work: reporting unused dependencies, reducing cache collisions and a min-publish-age feature.
Changes to Types and Memory Management
The never-type stabilization gives library and application authors a supported way to name a type that cannot have a value. This can make APIs that express impossible error cases or non-returning behavior more directly. Its compatibility implications deserve attention during upgrades, particularly for older-edition projects and their dependencies. Developers should treat compiler warnings and test failures as signals to review affected code rather than assume the change is purely internal.
The allocator API creates a stable foundation for custom allocation strategies in some standard-library containers. That can matter to library authors and systems software, but the release announcement cautions that support is not complete: additional APIs and more collection and pointer types remain outside the stabilized surface. DropGuard offers a compact way to run cleanup or rollback logic on scope exit, including when a function returns early with the ? operator. Cargo’s dependency and cache features also address practical concerns in managing larger projects, though the announcement does not quantify their performance effects.
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A Decade of Never-Type Work
The Rust team describes stabilization of the never type as the conclusion of a long-running effort: it took 10 years and five failed attempts, and completes the relevant project goal. One difficulty was the planned relationship between the never type and Infallible, an existing type used to represent errors that cannot occur. Making them compatible required a fallback behavior change, according to the announcement.
The allocator work is at an earlier stage. Rust 1.100 stabilizes the core trait and its use with Vec and Box, but the team says expanding the API and extending allocator support to more standard-library types remains future work. The release is available through the stable channel; users with rustup can update by running rustup update stable, according to the post.
“After 10 years and 5 failed stabilization attempts, the never type is finally stable!”
— Rust team, in the Rust 1.100.0 announcement
Compatibility Risks Still Need Testing
The announcement does not identify every code pattern or dependency that could be affected by the fallback change, nor does it provide a complete list of projects requiring updates. It says fixes have already been released for public crates and recommends updating a dependency that fails because of the never type. The practical impact for any individual project will depend on its code and dependency versions.
The announcement also does not give benchmarks or adoption data for the allocator API, DropGuard or the Cargo additions. Custom allocators currently work with Vec and Box, but the timeline for support in other standard-library types is not specified. The Cargo feature descriptions in the supplied release material do not include detailed behavior or configuration guidance.
Upgrade and Check Dependencies
Rust users can install the stable release with rustup update stable and consult the detailed 1.100 release notes for API and migration information. Teams using editions 2015, 2018 or 2021 should run their tests and review compiler warnings, particularly where generic return types or ignored results are involved. If a dependency fails after upgrading, the Rust team advises checking for a newer release that includes a fix.
The allocator API is expected to develop further, but the team has not provided dates for additional stabilization. Developers who want to test upcoming Rust changes can select the beta or nightly channel with rustup, the announcement says, and report bugs to the project.
Key Questions
What are the main features in Rust 1.100?
The release stabilizes the never type and core parts of the allocator API, adds DropGuard and a function for creating zero-sized types, and includes Cargo changes for unused-dependency reporting, cache collisions and min-publish-age.
Could Rust 1.100 break older Rust projects?
It can affect some uncommon code in editions 2015, 2018 and 2021, because the never-type fallback changes from unit type () to !. The Rust team says the effect should usually be unnoticeable, but advises reviewing warnings and tests after upgrading.
What does the stable allocator API support now?
The release stabilizes the Allocator trait and says custom allocators can currently be used with Vec and Box. The team says support for more standard-library types and additional API surface remains future work.
How do I install Rust 1.100?
If Rust is installed through rustup, run rustup update stable. The Rust team also recommends consulting the detailed release notes for the full set of changes.
Source: blog.rust-lang.org
