Yes—as a test, but I would not expect it to make one ordinary build faster. build-dir-new-layout reorganizes intermediates by package/build-unit hash; the intended wins are fewer cache/lock collisions, better behavior with concurrent Cargo processes, and groundwork for finer-grained/shared caching. Cold or warm single-process builds may be neutral or slightly slower.

Try it in an isolated target dir:

CARGO_TARGET_DIR=/tmp/target-v2 cargo +nightly -Zbuild-dir-new-layout build

Run several cold and warm repetitions, plus concurrent builds, and compare wall time/--timings against the same nightly with the temporary opt-out (if that nightly still supports it):

__CARGO_TEMPORARY_BUILD_DIR_NEW_LAYOUT_OPT_OUT=1 \
  CARGO_TARGET_DIR=/tmp/target-v1 cargo +nightly build

Recent nightlies have been changing the default, so -Zbuild-dir-new-layout may be redundant; cargo +nightly -Z help shows whether it is available. I’d try this on crane/selfci and report any breakage in tools that inspect target internals, rather than enable it globally expecting an immediate compile-speed win.