0.1.6 — RROQ158 SOTA Default at group_size=128

This release promotes the dim-aware Rroq158Config(group_size=128) lane to
the build-time default for newly created RROQ158 indexes — closing the
production-validation arc started in 0.1.5 (Phase 7 / Phase 8).

Highlights

• ~13% smaller per-token storage (~40 vs ~46 bytes/token at dim=128;
  ~6.4× smaller than fp16, up from ~5.5×).
• CPU p95 ~10–30% faster on the BEIR-6 mean (one fewer scale load per
  group in the popcount kernel; nfcorpus −22%, scifact −15%, scidocs −10%,
  fiqa within +2% noise).
• NDCG@10 within ±0.005 of the previous gs=32 baseline; per-dataset
  mean Δ vs gs=32 across BEIR-6 = +0.0006 — Pareto-equal in quality
  while delivering smaller storage AND lower-or-equal CPU p95 on every
  dataset measured.
• Dim-aware fallback _resolve_group_size(requested, dim)
  transparently steps down to gs=64 / gs=32 (with a log warning) on
  production corpora whose token dim is not divisible by 128, so the new
  default works on dim=64 / 96 / 128 / 160 alike without caller changes.

Headline BEIR-6 averages (rroq158 gs=128 default)

Codec	NDCG@10	R@100	GPU p95 (ms)	CPU p95 (ms)
fp16 (baseline)	0.5206	0.7360	4.0 (1.00×)	103 (1.00×)
rroq158 (gs=128, default)	0.5069	0.7298	4.8 (1.20×)	310 (3.00×)
rroq158 (gs=32)	0.5063	0.7282	4.8 (1.20×)	325 (3.15×)
rroq4_riem	0.5158	0.7345	8.5 (2.13×)	580 (5.63×)

Full per-dataset / per-codec sweep:
reports/beir_2026q2_gs128/.

Migration

Existing on-disk indexes are unaffected — the manifest carries the
build-time group_size and only newly built indexes pick up the new
default.

• Pin Rroq158Config(group_size=32) to restore the previous default
  exactly.
• Pin Rroq158Config(group_size=64) for the safest cross-dataset choice
  (covers high-intra-token-variance corpora like arguana).

See docs/guides/quantization-tuning.md
for the full decision matrix and per-dim recipe table.

Install

pip install --upgrade voyager-index==0.1.6
# native (optional, for the Rust SIMD CPU kernel + tabu solver):
pip install --upgrade voyager-index[native]==0.1.6
# full (server + multimodal + native + GPU triton):
pip install --upgrade voyager-index[full,gpu]==0.1.6

Full changelog and merged PRs in
CHANGELOG.md.