turboquant_plus/refract

REFRACT v0.1

REFerence-anchored Robust Acid-test for Compressed Transformers.

A benchmaxx-resistant alternative to corpus PPL for evaluating KV-cache quantization quality. Replaces "lower PPL = better" — a metric the paper docs/papers/attn-rotation-and-ppl-artifact.md shows can invert sign on instruct-tuned models — with a composite of two fp16-anchored axes that ranks configurations by distance from the fp16-KV reference, not by absolute corpus likelihood.

What v0.1 ships

Two of the four planned axes:

Axis	What it measures	Scoring
A — GTM (Greedy Trajectory Match)	For K diverse prompts, do the reference and candidate produce identical greedy completions?	100 * full_match_rate
B — KLD@D (KL Divergence vs reference, corpus proxy)	Mean KL divergence between candidate and reference distributions, via llama-perplexity --kl-divergence.	100 * exp(-mean_kld_nats)

Composite: REFRACT = harmonic_mean(GTM, KLD) clipped to [0, 100].

Bands: [90,100] EXCELLENT · [80,90) PASS · [60,80) DEGRADED · [0,60) FAIL.

Why this exists

The paper shows that on gemma-4 26B-A4B-Q8 at q8/turbo4 KV, corpus PPL on wikitext-2 says rotation OFF "wins" by 42% — but KLD vs the fp16-KV reference says the same configuration is 1.7 nats away from fp16, the largest drift on the row. The §4.5 noise floor on the KLD codepath is bit-exact zero on Metal, so the signal is real. PPL is reading mis-calibration as improvement.

REFRACT rejects the PPL framing entirely: nothing matters except how close the quantized model's behaviour stays to its fp16 self.

Install

REFRACT is part of the turboquant package. From the repo root:

pip install -e .

Stdlib + the existing numpy/scipy deps; no new pip requirements.

Required external binaries

REFRACT shells out to llama-cli and llama-perplexity. By default it looks in ~/local_llms/llama.cpp/build-test/bin. Override:

export LLAMA_CPP_BIN_DIR=/path/to/llama.cpp/build/bin

Quickstart

python3 -m refract.cli score \
    --model ~/local_llms/models/Qwen2.5-7B-Instruct-Q8_0.gguf \
    --reference 'ctk=f16,ctv=f16' \
    --candidate 'ctk=q8_0,ctv=turbo4,attn_rot_v=0' \
    --prompts refract/prompts/v0.1.jsonl \
    --corpus ~/local_llms/llama.cpp/wikitext-2-raw/wiki.test.raw \
    --chunks 32 -c 512 -ngl 99 \
    --measure-floor \
    --json-out refract.qwen.json

Sample output (illustrative — real numbers depend on the model and build):

========================================================================
 REFRACT v0.1 — Reference-anchored Robust Acid-test
========================================================================
 model     : Qwen2.5-7B-Instruct-Q8_0.gguf
 reference : ctk=f16,ctv=f16
 candidate : ctk=q8_0,ctv=turbo4,attn_rot_v=0
 timestamp : 2026-04-29T11:14:02
------------------------------------------------------------------------
 Noise floor (ref vs ref):  99.99  (min 99.5)  [OK]
------------------------------------------------------------------------
 REFRACT     :  92.40  [######################################--]  EXCELLENT

 Axis A GTM  :  93.33  [######################################--]
 Axis B KLD  :  91.50  [#####################################---]
------------------------------------------------------------------------
 GTM diagnostics
   prompts                    : 30
   tokens decoded each        : 128
   full match rate            :  93.3 %
   median first divergence    : token 47
   mean prefix agreement      : 121.4 tokens

 KLD diagnostics
   chunks x ctx               : 32 x 512
   mean KLD (nats)            : 0.088732
   candidate PPL              : 6.146
   RMS Δp (vs reference)      : 3.13 %
   same top-p (vs reference)  : 95.59 %
========================================================================

CLI flags

Flag	Default	Notes
--model PATH	required	GGUF path
--reference SPEC	ctk=f16,ctv=f16	KV config string (see below)
--candidate SPEC	required	KV config string
--prompts PATH	required	JSONL prompts file
--corpus PATH	required	plain-text corpus for KLD
--chunks N	32	--chunks for llama-perplexity
-c N	512	context size
-ngl N	99	GPU layers
--n-predict N	128	tokens per GTM prompt
--seed N	42	greedy seed
--measure-floor	off	Run REFRACT(ref, ref) and abort if < 99.5
--json-out PATH	—	Write the full report as JSON
--no-progress	off	Suppress per-prompt progress lines

KV config spec format

key=value,key=value,...

Key	Effect
ctk	-ctk <val> (e.g. f16, q8_0, turbo4)
ctv	-ctv <val>
attn_rot_k	LLAMA_ATTN_ROT_K_OVERRIDE=<val>
attn_rot_v	LLAMA_ATTN_ROT_V_OVERRIDE=<val>
attn_rot_disable	LLAMA_ATTN_ROT_DISABLE=<val> (hard lockout)
any other	passed through as --<key> <value>

Validation

tests/test_validation.py reproduces the gemma-4 26B-A4B q8/turbo4 OFF cell from the paper and asserts that REFRACT lands in DEGRADED or FAIL. PPL on this cell would say "win" (-42%); REFRACT must say "audit" or "fail".

It is marked integration because it spawns llama.cpp many times against a 26B model. To run:

# Mark it in pytest.ini if not already:
#   markers = integration: marks tests requiring llama.cpp + a real GGUF
pytest -m integration refract/tests/test_validation.py -s

Or directly via CLI:

python3 -m refract.cli score \
    --model ~/local_llms/models/gemma-4-26B-A4B-Q8_0.gguf \
    --reference 'ctk=f16,ctv=f16' \
    --candidate 'ctk=q8_0,ctv=turbo4,attn_rot_v=0,attn_rot_k=0' \
    --prompts refract/prompts/v0.1.jsonl \
    --corpus ~/local_llms/llama.cpp/wikitext-2-raw/wiki.test.raw \
    --chunks 32 --measure-floor

Fast unit tests (no subprocess) live in tests/test_unit.py.

File layout

refract/
  __init__.py
  cli.py                    # CLI entry point
  score.py                  # composite + bands + floor logic
  axes/
    __init__.py
    gtm.py                  # Axis A: greedy trajectory match
    kld.py                  # Axis B: KLD via llama-perplexity
  runner.py                 # llama.cpp subprocess wrappers + KVConfig
  report.py                 # text + JSON report formatter
  prompts/
    v0.1.jsonl              # 30 CC0 prompts
  tests/
    test_unit.py            # math + parser tests, no subprocess
    test_validation.py      # paper-cell reproduction (integration)
  README.md

v0.2 roadmap (deferred — explicitly NOT in v0.1)

• Axis C — R-NIAH: retrieval needle-in-a-haystack at long context. The paper ends with "a more rigorous downstream probe... would likely surface degradation that simple factual completions hide" — R-NIAH is that probe.
• Axis D — PLAD: Perturbation-Locality Aware Drift. Measures whether drift is concentrated on specific layers or token positions, which the paper §3.6 nrot-ablation hints is mechanistically informative.
• True trajectory KLD: capture per-step logits during generation in GTM's forward pass instead of using corpus-KLD as a proxy. Requires a small llama.cpp change (or a custom binary fork) to dump logits.
• Token-level diff via llama-tokenize instead of whitespace split, so GTM diff positions match real BPE/SP token indices.

Known limitations of v0.1

• KLD axis is a corpus proxy, not true trajectory KLD. Acknowledged TODO in axes/kld.py.
• GTM diff is whitespace-tokenised. Acknowledged TODO in axes/gtm.py.
• We strip llama-cli noise patterns by regex; new noise lines from a future llama.cpp release would slip through. Add to _NOISE_PATTERNS in runner.py if you see them.
• Floor is checked at composite level (≥ 99.5). Per-axis floor is implied but not separately reported. Consider adding for v0.2.