---
license: apache-2.0
language: en
library_name: transformers
tags:
- text-compression
- token-classification
- modernbert
- lora
- kompress
base_model: answerdotai/ModernBERT-base
pipeline_tag: token-classification
---

# kompress-v2-base

Extractive prompt compressor for LLM proxies. Predicts a keep/drop label per
token; the surviving tokens form a compressed version of the input that
preserves meaning while reducing token count.

Based on **ModernBERT-base** (149M params) with a LoRA adapter (3.4M trainable
params, 2.2%) plus a custom dual head (token classifier + 1-D span conv).
Trained on 126,617 accepted Pipeline A+B labels (compressor + faithfulness
judge) across 17 domains: narrative, dialog, code, agent traces, healthcare,
finance, government, scientific, web, summary, and tool-calling.

## Quick start

```python
import torch
from transformers import AutoTokenizer

# Option A: load the merged checkpoint (no LoRA needed)
state = torch.load("merged.pt", map_location="cpu")

# Option B: load via the kompress package
from kompress.model.architecture import HeadroomCompressorV2
from kompress.model.config import V2_BASE
import json

with open("config.json") as f:
    cfg_dict = json.load(f)
cfg = V2_BASE  # or rebuild from cfg_dict
model = HeadroomCompressorV2(cfg)
model.load_state_dict(torch.load("merged.pt", map_location="cpu"), strict=False)
model.eval().cuda()

tokenizer = AutoTokenizer.from_pretrained("chopratejas/kompress-v2-base")

# Compress
text = "The quick brown fox jumps over the lazy dog."
enc = tokenizer(text, return_tensors="pt").to("cuda")
with torch.no_grad():
    out = model(**enc)
scores = out["final_scores"][0]    # P(keep) per subword
keep = (scores >= 0.5)
kept_tokens = enc["input_ids"][0][keep]
print(tokenizer.decode(kept_tokens, skip_special_tokens=True))
```

## Threshold tuning

The model emits `final_scores ∈ [0, 1]` per subword. Adjust the threshold to
trade compression aggressiveness for must-keep recall.

| Threshold | keep_rate | must_keep_recall | F1 | best for |
|---|---|---|---|---|
| **0.30** | 0.917 (8% drop) | 0.994 | 0.904 | Conservative |
| **0.40** | 0.867 (13% drop) | 0.987 | 0.913 | Safe |
| **0.50** (default) | 0.815 (18% drop) | 0.974 | **0.918** | Balanced |
| **0.60** | 0.765 (23% drop) | 0.950 | 0.915 | Aggressive |
| **0.70** | 0.705 (30% drop) | 0.908 | 0.898 | Very aggressive |

Evaluated on the held-out test split (n=7,037 examples, stratified by domain).

## Training data

- **126,617 labeled examples** after `min_drop_ratio=0.05` filtering and
  same-conversation packing.
- **Sources**: arxiv, pubmed-scientific, govreport, swe-smith, swe-gym-openhands,
  toolmind, xlam-fc, fineweb-edu, cnn-dailymail, xsum, glaive-fc, lmsys-chat,
  claude-code-sessions, meetingbank, the-stack-smol-md, samsum, swe-bench-verified.
- **Labeler**: DeepSeek-V4-Flash (compressor) + DeepSeek-V4-Pro (judge) with
  Pipeline A + B faithfulness loop. Hard-keep overlay enforces names, dates,
  numbers, URLs, code identifiers via GLiNER + regex + lexicons.
- **Bucket split**: short=48%, mid=31%, long=21% (max_length 8,192 native
  ModernBERT context).
- **Split**: train=126,617 / val=7,037 / test=7,037.

## Training details

- Base: ModernBERT-base (149M params)
- Encoder fine-tuning: **LoRA** (r=16, alpha=32, target_modules=Wqkv/Wi/Wo)
- Heads: per-token CE (must-keep loss weight = 3.0) + 1-D span conv (BCE,
  weight 0.3 on total loss)
- Trainable params: 3.4M (2.2% of total)
- Loss: weighted cross-entropy on token head + BCE-with-logits on span head
- Optim: AdamW (lr=2e-4 cosine, warmup_ratio=0.06, weight_decay=0.01)
- Effective batch: 48 (12 × 4 grad-accum)
- Epochs: 3
- Precision: bf16 with FlashAttention-2 + gradient checkpointing
- Hardware: 1×H100 80GB, ~39 min wall-clock

## Final metrics (test split, threshold=0.5)

- eval_f1: 0.918
- eval_must_keep_recall: 0.974
- eval_keep_rate: 0.815 (18% compression)
- eval_loss: 0.34

## Files in this repo

```
config.json           # KompressV2Config + arch metadata
model.safetensors     # ~600 MB — best checkpoint, LoRA merged into the encoder
merged.pt             # ~600 MB — full state dict, alias for safetensors load
tokenizer.json        # ModernBERT-base tokenizer
tokenizer_config.json
special_tokens_map.json
adapter/              # LoRA adapter ONLY (~30 MB), for stacking per-org adapters
  adapter_config.json
  adapter_model.safetensors
  token_head.pt
  span_conv.pt
README.md             # this file
```

## License

Apache 2.0. Free for commercial use. ModernBERT base is also Apache 2.0.

## See also

- [`chopratejas/kompress-v2-large`](https://huggingface.co/chopratejas/kompress-v2-large)
  — larger variant (ModernBERT-large, 395M params, private/enterprise)
- Headroom proxy integration guide:
  [docs/CUSTOMER_QUICKSTART.md](https://github.com/chopratejas/kompress/blob/main/docs/CUSTOMER_QUICKSTART.md)
- Per-org fine-tuning (LoRA stacking):
  [docs/DEPLOYMENT_STRATEGY.md](https://github.com/chopratejas/kompress/blob/main/docs/DEPLOYMENT_STRATEGY.md)