BINARY

One bit per dimension, the sign: 1/32 of the memory traffic, and the scan becomes popcounts.

Far coarser than INT8 — it keeps direction and discards magnitude entirely — and the measurement says so plainly. At the same oversampling that makes INT8 exact it recovers only about 85% of the entries an exact scan would have found. Reaching 98% takes six times the shortlist, which is what it is set to, and that is the honest cost: the scan is 32 times cheaper and the rescoring pass is six times longer. Worth it when the scope is large enough that the scan dominates, and not otherwise.