load_calib tokenizes with tok(..., truncation=True, max_length=seqlen). For a
fast tokenizer that mutates the Rust backend's truncation state in place, and
the subsequent tok.save_pretrained() persisted it, so every mixed-NVFP4 build
shipped a tokenizer.json carrying
"truncation": {"direction": "Right", "max_length": 2048, ...}
against a source whose value is null. Every prompt was clamped at the
calibration length, permanently.
It hid because older transformers does not enforce the text-vs-ids count
check. On a newer one the seat dies at startup with a message that names
images and never mentions tokenizers:
ValueError: Mismatch in `image` token count between text and `input_ids`.
Got ids=[2047] and text=[16384].
The cap also silently limited image resolution well before it killed
anything -- at 2048 the largest servable image is about 1448x1448, since
(edge/patch)^2 / merge^2 image tokens have to fit under it.
Fix saves a pristine tokenizer re-read from the source rather than the
mutated calibration object, and then asserts truncation is null so the
defect fails the build instead of shipping again.
Playbook gains section 3.14 with the symptom, the cause, the audit one-liner
and a table of which builds were affected, plus a fourth mandatory post-step.
The transferable lesson is called out: this is the third case of an artifact
carrying config authored against an older transformers that a newer one
begins enforcing, so an image bump is a config-compatibility event rather
than just a version change.
Quantized the L35 abliterated model to mixed NVFP4 and measured MTP acceptance
end to end. The experiment's whole premise: Heretic (the incumbent gen seat)
leaves the MTP head a byte-identical base graft its wrapper never loads, whereas
Robinson abliterates the MTP head in-band — the question was whether that in-band
edit survives well enough to spec-decode. It does, better than the graft:
MTP acceptance 59.1% median (51-65%, 8 cache-busted topics) vs incumbent ~47%
decode 118.7 tok/s median (faster; image-confounded, read as not-worse)
abliteration survives quant (creative refusals drop, self-harm guardrail
intact, coherent)
Output at /tank/aimodels/qwen38-27b-coldfusion-L35-nvfp4-mixed (22.5 GB). Result
JSON in bench/. NOT cut over — the incumbent seat is untouched; making L35 the gen
seat is a separate decision needing the full Stage-3 gate + real multi-turn hold.
Two env foot-guns hardened along the way:
- quant_mixed_nvfp4.py now promotes text_config attention fields
(num_attention_heads etc.) to the top-level config for the oneshot, then
restores. transformers 5.10 / llmcompressor 0.12 (this venv moved under us
since the Aug-15 heresy quant) no longer delegate the top-level lookup, so
oneshot raised "Cannot determine num_attention_heads". Same "the fight is the
environment" pattern as the abliteration capture.
- a sub-~23GB quant saves as a single model.safetensors with no index, so the
post_quant MTP graft needed an index built first — from the safetensors header,
not safe_open (which mmaps the whole shard and ENOMEMs on ZFS).
post_quant grafted the abliterated MTP (15 tensors, 849 MB) and re-injected
re:^mtp.* into quantization_config.ignore (llm-compressor pruned it again — the
two-rounds-lost 0%-MTP bug, fired and repaired as designed). Probe served on the
pinned nightly (#51113 qwen3_5_mtp fix) to match the live seat's vLLM.
Re-quantizes the fleet `gen` seat from weight-only NVFP4A16 to a
mixed-precision build: NVFP4 W4A4 for layers 0-55 MLPs, FP8 W8A8 for the
attention projections / linear_attn / lm_head / layers 56-63 MLPs, FP8 KV
cache. Replicates the scheme of unsloth/Qwen3.8-27B-NVFP4 on the
abliterated weights.
The queued task named this "W4A8" (NVFP4 weights + FP8 activations). That
checkpoint cannot be served: vLLM 0.24's compressed-tensors dispatcher
(compressed_tensors.py:704-713) accepts NVFP4 weights with either no input
quantization (W4A16, which forces the Marlin kernel) or NVFP4 input
quantization (W4A4) -- anything else, FP8 included, raises ValueError at
load. CompressedTensorsW4A8Fp8 is INT4 weights gated on an exact-sm90
check, so it is closed on Blackwell twice over. The ~20% intuition was
correct; the scheme name was not. Getting FP8 into the mix has to be done
per-layer-group.
Established the gain before spending GPU time: unsloth's build was already
on-box, so serving it as a probe measured +19.1% over our seat at identical
MTP acceptance -- a kernel-level result, no requant needed to learn it.
Measured, cache-busted, bs=1:
decode 80.12 -> 94.53 tok/s (+18.0%)
MTP acceptance 47.8% -> 47.7% (unchanged)
perplexity (n=6) 6.941 -> 7.059 (+1.7%)
abliteration 4/4 -> 4/4 (preserved)
weights on disk 27.7 -> 22.5 GB (-19%)
Surface test green on the live seat: plain chat, vision, tool calling,
thinking split, 36K-token needle retrieval, streaming. All 7 LiteLLM
aliases verified routing.
GEN_GPU_MEM_UTIL 0.45 -> 0.43: the new weights are 5.2 GB smaller, and at
0.45 the seat absorbed that slack as KV, leaving meromero-charrp 0.18 GiB
short of its budget on the shared GPU0 -- it crash-looped. Handing the
space back leaves gen 422K tokens of KV (1.6x its 262K context) and both
seats co-resident at 89.8/97.9 GB.
Also records two measured negatives so they are not re-chased:
GEN_SPEC_TOKENS is already optimal at 3 (swept 2/3/4/5 -> 77.1/80.1/78.7/
75.9 tok/s), and vLLM's prompt_logprobs are ~uniform while speculative
decoding is on, so perplexity must be measured with spec off.
Pipeline, acceptance harness and raw measurements land in
services/gen-seat-mixed-quant/. Rollback is one .env line; the previous
build is untouched at /tank/aimodels/qwen38-27b-uncensored-nvfp4.
vh