Rust merges an MVP of the custom Allocator API
Rust merged a partial stabilization of allocator_api: the Allocator trait and custom-allocator support for Box and Vec. This is an important step toward arena and other custom allocation strategies, but it is deliberately an MVP; broader standard-library collection support and follow-on allocator APIs remain future work.
The Reddit thread corrected an old tracking issue whose summary no longer described the current state. Discussion also focused on the long stabilization history, API naming, soundness constraints, and the limits of the initial surface. The merge is confirmed in the stabilization PR; the subreddit post says it is on track for Rust 1.100.