---
license: apache-2.0
library_name: sentence-transformers
pipeline_tag: feature-extraction
base_model: ThakiCloud/SKILLRET-Edge-22M
base_model_relation: quantized
datasets:
  - ThakiCloud/SKILLRET
language:
  - en
tags:
  - sentence-transformers
  - feature-extraction
  - retrieval
  - skill-retrieval
  - agent
  - on-device
  - mixed-precision
  - quantization
---

# SKILLRET-Edge-22M-drift-mixed

The **22.7M-parameter** SKILLRET-Edge bi-encoder for **agent skill retrieval**, quantized to a
**mixed-precision** layout chosen by a **label-free drift signal** instead of one uniform bit width.
Same architecture, same tokenizer, same query contract as `ThakiCloud/SKILLRET-Edge-22M-int4` — this
repo exists to show a *different allocation technique*, not to replace the int4/int3 variants.

Scored on the public `ThakiCloud/SKILLRET` **test split** (4,392 queries / 6,006 skills).

**NDCG@10 74.57** · **14.1 MB packed** (the int3 file size, 99.1% of fp16)

## Where it sits

| Variant | Packed size | NDCG@10 | Note |
|---|---|---|---|
| fp16 | 45.4 MB | 75.25 | reference |
| int4 / g16 (uniform) | 17.0 MB | 75.14 | best quality per the int4 card |
| **drift-mixed / g16 (this repo)** | **14.1 MB** | **74.57** | int3 bytes, +0.65pp over int3 |
| int3 / g16 (uniform) | 14.2 MB | 73.82 | |
| int2 / g16 (uniform) | 11.9 MB | 59.73 | 4.18 real bits — no size win over int4 g128 |

Paired query-level bootstrap on the same 4,392 queries (5,000 resamples), all arms built and scored
under one protocol (int3 uniform comes from the 5.2-bit run of the same series):

| Contrast | Δ NDCG@10 [95% CI] |
|---|---|
| drift-mixed (14.1 MB) − uniform int3 g16 (14.65 MB, same protocol) | +0.65pp [+0.35, +0.96] |
| drift-mixed at the *same* 5.2-real-bit budget − uniform int3 | +0.98pp [+0.64, +1.33] |
| drift-mixed − uniform int2 g16 | +14.83pp [+14.08, +15.59] |
| drift-mixed − label-supervised allocation (per-module ΔNDCG, same budget) | +0.71pp [+0.43, +0.99] |
| drift-mixed − 5 random allocations at the same bytes | +7.7 to +9.6pp (every CI excludes 0) |

Read the first row honestly: the gain over uniform int3 is real but under one point. The value of the
technique is the **ordering** (random allocations at the same bytes lose 8–9 points), and the budgets
uniform cannot express — at 4.5 real bits (~12.7 MB) the drift allocation keeps **70.42**
where uniform int2 gives 59.73 and uniform int3 does not fit.

## How the bits were allocated

Each of 12 allocation units was quantized **alone** at 2/3/4 bits while the rest stayed fp32, and the
resulting *drift* of the output embeddings — mean (1 − cosine) between full-precision and quantized
embeddings, averaged over 1,500 calibration skills and 150 calibration queries, balanced across the two
— was recorded. No relevance labels are used. An exhaustive integer program then picks the per-unit
bit width that minimises predicted drift under a hard byte budget (fp16 scale + zero per group of 16
counted). The drift ordering reproduced across disjoint calibration halves at every size tried
(Spearman 1.000 at 75/150/300/600 queries); the label-based ordering on this model did **not**
(−0.29 to +0.34), which is why the label-supervised row above is reported but not recommended.

| Unit | What it covers | Params | Bits |
|---|---|---|---|
| `embedding.v0` | word embedding rows 0–25% | 2.93M | **3** |
| `embedding.v1` | rows 25–50% | 2.93M | **2** |
| `embedding.v2` | rows 50–75% | 2.93M | **2** |
| `embedding.v3` | rows 75–100% | 2.93M | **2** |
| `attention.b0` | attention, layers 0–1 | 1.18M | **3** |
| `attention.b1` | attention, layer 2 | 0.59M | **4** |
| `attention.b2` | attention, layers 3–4 | 1.18M | **4** |
| `attention.b3` | attention, layer 5 | 0.59M | **4** |
| `ffn.b0` | FFN, layers 0–1 | 2.36M | **3** |
| `ffn.b1` | FFN, layer 2 | 1.18M | **3** |
| `ffn.b2` | FFN, layers 3–4 | 2.36M | **4** |
| `ffn.b3` | FFN, layer 5 | 1.18M | **3** |

The picture is the one you would guess after seeing the sensitivities: the word-embedding table is
51.6% of the parameters and its lower-frequency rows barely move the output at 2 bits, while the
middle attention/FFN blocks are where 2-bit damage concentrates.

## Files

| File | What it is |
|---|---|
| `model.safetensors` | The quantized values **de-quantized back into fp16** so `sentence-transformers` loads it today. This file produces the score above (re-evaluated after packing: 74.569 vs the ledger's 74.559). |
| `model-drift-mixed-g16.bin` | The **actual packed payload — 14.140 MB**: per-unit bit-packed indices + fp16 scale/zero per 16 weights, plus the two small fp16 position/token-type tables. Predicted 14.140 MB, 0.0% error. |
| `quantization.json` | The plan (`plan`), per-unit parameter counts, and the per-tensor layout (name, rows slice, bits, offset) if you want to write a kernel. |
| `query_prefix.json` | `resolved: ""` — encode queries **bare**, no instruction prefix. |

The safetensors path runs fp32 arithmetic; latency is identical to the int4/int3 cards (same
architecture, same dequantized format) and is *not* an integer-kernel speed.

## Usage

```python
from sentence_transformers import SentenceTransformer
m = SentenceTransformer("ThakiCloud/SKILLRET-Edge-22M-drift-mixed")
q = m.encode(["I need to convert a spreadsheet into a chart"], normalize_embeddings=True)
d = m.encode(["Chart Builder — turn tabular data into bar/line charts"], normalize_embeddings=True)
print(q @ d.T)
```

## Caveats

- Standard error on this split is about ±0.45; the drift-vs-int3 gap is significant only because it is
  paired on the same queries. Do not read it as a ranking between cards scored in different runs.
- The protocol matches the other Edge cards: CLS pooling, L2-normalised, `max_length=256`, bare queries.
- Mixed precision means a real integer kernel has to handle per-tensor (and, for the embedding table,
  per-row-band) bit widths. That is the cost you pay for +0.65pp at int3 bytes.
- The base student, the distillation recipe and the int4/int3 measurements are documented on
  `ThakiCloud/SKILLRET-Edge-22M-int4`.

## License

Apache-2.0, inherited from the base model.

## Citation

Benchmark: [SkillRet, arXiv:2605.05726](https://arxiv.org/abs/2605.05726)

Student and uniform-PTQ measurements:
[Where Post-Training Quantization Breaks Text Embedders, arXiv:2609.16391](https://arxiv.org/abs/2609.16391)

Allocation signal (the drift criterion and the allocator used here):
*Quantize by Drift: Label-Free Mixed-Precision Post-Training Quantization for Text Embedders*, Han, 2026 —
arXiv preprint, identifier to be added on announcement.

```bibtex
@article{han2026quantizebydrift,
  title   = {Quantize by Drift: Label-Free Mixed-Precision Post-Training Quantization for Text Embedders},
  author  = {Han, Hyojung},
  journal = {arXiv preprint},
  year    = {2026}
}
```