topabaem
/

LTX-2.5-Text-Encoder-4bit-8GB

+# A100 / current-upstream ladder (2026-08-20)
+Rebuilt against the encoder Lightricks published on 2026-08-17 (commit
+`1b92891c`, *"Aligns the published encoders with the LTX-2.5 model
+checkpoints"*). Everything measured before that date used the superseded,
+misaligned encoder and is not comparable to what is here.
+Runtime: Colab A100-SXM4-40GB (cc 8.0), torch 2.11.0+cu128, transformers 5.14.1
+pinned, plan `r45c`, calibration `calib-large.txt`, reference regenerated on this
+card from the current source.
+## Gate — A3 wins on every axis
+| | A0 `legacy` | **A3 `bypass` + group bounded 12:1** |
+|---|---:|---:|
+| video mean relL2 | 0.06061 | **0.05204** (−14%) |
+| audio mean relL2 | 0.06095 | **0.04827** (−21%) |
+| video worst | 0.14733 | **0.09187** (−38%) |
+| audio worst | 0.14440 | **0.10573** (−27%) |
+| video cosine | 0.99763 | **0.99848** |
+| `\|\|Q\|\|/\|\|W\|\|` | 302.654 | **4.216** (72x) |
+| columns zeroed | 5 | **0** |
+| max restore gain | 469.56 | **19.00** |
+| damping escalation | 1x | 10x |
+The trade this project spent two sessions quantifying is gone. On the
+superseded source and a V100, the structural fix cost about 6% of conditioning
+drift; here it costs nothing and improves the worst case most.
+Both figures reproduced to five decimals across two independent A100 runtimes,
+so builds are deterministic within an architecture even though they are not
+across architectures.
+## Render prompts, against a BF16 conditioning from the same card
+| # | A0 | A3 | prompt |
+|---:|---:|---:|---|
+| 0 | 0.05870 | **0.05073** | humanoid robot, freight elevator |
+| 1 | 0.07487 | **0.06596** | robotic hand, cracked ceramic cup |
+| 2 | **0.05551** | 0.08213 | four-legged inspection robot |
+| 3 | 0.05061 | **0.04489** | dozens of small wheeled robots |
+| 4 | 0.08887 | **0.05286** | rescue robot in smoke |
+| mean | 0.06571 | **0.05931** | |
+| worst | 0.08887 | **0.08213** | |
+A3 is better on four of five. Prompt 2 is the exception, and it was also the
+exception on the superseded source with a V100 - the same prompt moving the same
+way after both the weights and the architecture changed is a signal, not noise,
+though five prompts cannot say what it means.
+## Visual
+`frames/cmp-*.png` puts BF16, A0 and A3 side by side - same card, same DiT, same
+seeds, same prompts.
+* **Prompt 0 now renders an actual robot.** Dome head, two amber eyes, segmented
+  neck, panelled torso, in all three. The superseded encoder produced a
+  human-faced android for the same prompt. That improvement comes from the
+  source alignment, not from anything this project did.
+* BF16 and A3 track each other closely - same badge colour on prompt 0, glasses
+  present on prompt 1 - while A0 differs on both.
+* Prompt 1 still fails to a human face in all three including BF16. Model limit,
+  not compression damage.
+## Artifacts
+On the Hub at `topabaem/LTX-2.5-TextEncoder-nvfp4-portable` (private), pushed by
+the build worker as each stage finished rather than downloaded afterwards:
+`A0.packed.safetensors`, `A3.packed.safetensors`, and `evidence/` carrying the
+gate JSON, build logs with per-layer drift and `||Q||/||W||`, the A100 BF16
+reference, all three conditionings and all fifteen clips.
+That push-as-you-go arrangement exists because three Colab runtimes died
+mid-build, twice destroying finished artifacts. The render stage then failed
+three times on a missing `gguf` package - and cost only the render, because the
+builds were already safe on the Hub.