---
language:
- ko
- en
license: apache-2.0
library_name: transformers
pipeline_tag: token-classification
base_model: openai/privacy-filter
tags:
- token-classification
- ner
- pii
- privacy
- pii-masking
- korean
- finance
- bioes
- viterbi
- mixture-of-experts
datasets:
- BCCard/pii-masking-openpii-finance
metrics:
- f1
- precision
- recall
---

# 1. Overview
A Korean/English **PII detection model for the finance domain**, built by full fine-tuning
[`openai/privacy-filter`](https://huggingface.co/openai/privacy-filter) (1.4B MoE, 50M active) on synthetic finance-domain PII data. It tags **18 PII entity types** (73 BIOES classes) at token level and is intended as the **NER layer of a multi-layer PII-masking gateway** in front of LLM services —
behind a regex backstop for fully structured identifiers, never as a standalone compliance guarantee.

On held-out validation it reaches **strict span-F1 0.956 (ko) / 0.969 (en)**. On an independent, adversarially-hardened Golden Set it holds **0.944 (ko) / 0.907 (en)** with **masking coverage 0.996 (ko) / 0.998 (en)** — i.e. ≥99.5% of gold PII characters are covered by predicted spans.

## 1.1. TL;DR
* **Base model**: [`openai/privacy-filter`](https://huggingface.co/openai/privacy-filter) — 1.4B-parameter MoE (128 experts, 50M active), 8 layers, hidden 640, bidirectional banded attention (±128), o200k tokenizer
* **Domain / Language**: Finance (BC Card — cards, accounts, national IDs, customer service text) / Korean + English
* **Task**: Token classification (BIOES) → character-offset PII spans → masking
* **Labels (18)**: `PERSON, RRN, FRN, CARD_NUMBER, ACCOUNT_NUMBER, SECRET, USER_ID, EMAIL, PHONE, PASSPORT, DRIVER_LICENSE, GENERIC_ID, ADDRESS, ZIPCODE, DATE, CARD_EXPIRY, CVC, IPIN`
* **Method**: Full fine-tuning (all parameters incl. experts & router) with a re-initialized 73-class head (rows copied from the base head by taxonomy mapping)
* **Decoding**: **constrained BIOES Viterbi** (not per-token argmax) + whitespace span refinement — the bundled `viterbi_calibration.json` exposes precision↔recall operating-point biases without retraining
* **Format**: BF16 (attention `sinks` kept FP32), single safetensors + tokenizer + label taxonomy + Viterbi calibration sidecar
* **Sequence length**: trained on sequences ≤768 tokens — chunk longer inputs
* **Intended use**
  - In-house **PII masking gateway** (detect → mask before text reaches an LLM)
  - Korean-centric finance text with mixed English (IDs, e-mails, card numbers)

## 1.2. Label Taxonomy (N=18)
The 18 labels re-map the upstream ai4privacy source labels to the granularity a Korean financial masking policy needs - merging fragments into single spans (`GIVENNAME`/`SURNAME` → `PERSON`, `CITY`/`STREET`/`BUILDINGNUM` → `ADDRESS`) and adding Korea-specific classes absent upstream (`RRN`, `FRN`, `IPIN`, `CARD_EXPIRY`, `CVC`, `SECRET`). `data source` records the row-source buckets in which each label occurs: `ko` means `openpii-1.5m-ko`, `en` means `openpii-1.5m-en`, and `domain` means locally synthesized rows.

| label | description | data source |
|-------|-------------|-------------|
| `PERSON` | full name (surname + given, single span) | ko, en, domain |
| `RRN` | resident registration number (Korea) | ko, domain |
| `FRN` | foreign registration number | domain |
| `CARD_NUMBER` | credit/debit card PAN | ko, en, domain |
| `ACCOUNT_NUMBER` | bank account number | ko, domain |
| `SECRET` | auth secret (password / API key / token) | ko, domain |
| `USER_ID` | online member ID | ko, en, domain |
| `EMAIL` | email address | ko, en, domain |
| `PHONE` | phone number (mobile / landline) | ko, en, domain |
| `PASSPORT` | passport number | ko, en, domain |
| `DRIVER_LICENSE` | driver's license number | ko, en, domain |
| `GENERIC_ID` | generic identifier (no KO counterpart) | ko, en, domain |
| `ADDRESS` | address (city / street / building, single span) | ko, en, domain |
| `ZIPCODE` | postal code | ko, en, domain |
| `DATE` | date / time | ko, en, domain |
| `CARD_EXPIRY` | card expiry date | domain |
| `CVC` | card verification code | domain |
| `IPIN` | I-PIN number | domain |

Each entity type has `B-`, `I-`, `E-` and `S-` boundary classes, plus the background class `O`. This yields 73 output classes. The bundled `label-taxonomy.yaml` and `config.json` must remain in the same label order.

## 1.3. Usage

```python
import torch
from transformers import AutoModelForTokenClassification, AutoTokenizer

model_id = "BCCard/MoAI-Privacy-Filter"
tokenizer = AutoTokenizer.from_pretrained(model_id)
model = AutoModelForTokenClassification.from_pretrained(model_id)
model.eval()

text = "고객 모아이님(000000-0000000)께서 010-0000-0000로 연락 요청하셨습니다."
enc = tokenizer(text, return_offsets_mapping=True, add_special_tokens=False, return_tensors="pt")
offsets = enc.pop("offset_mapping")[0].tolist()

with torch.no_grad():
    logits = model(**enc).logits[0]          # [T, 73] — raw output

# 1) Decode the logits with constrained BIOES Viterbi (recommended; see note below)
#    and map token paths to character spans via `offsets` — the detector's output:
# -> [{"start": 3, "end": 6, "label": "PERSON"},   '모아이'
#     {"start": 8, "end": 22, "label": "RRN"},     '000000-0000000'
#     {"start": 26, "end": 39, "label": "PHONE"}]  '010-0000-0000'
# 2) Masking is downstream application logic — replace each span according to
#    your masking policy, e.g.:
# -> "고객 [PERSON]님([RRN])께서 [PHONE]로 연락 요청하셨습니다."
```

> **Decoding note** — this model (like its base) is post-trained for **constrained Viterbi decoding**
> over the BIOES transition grammar, *not* independent per-token argmax. Argmax can emit invalid tag
> sequences (span splits / orphan tags) and measurably lowers span-F1. The bundled
> `viterbi_calibration.json` follows the upstream operating-point schema: its six transition biases
> shift the precision↔recall trade-off at deploy time without retraining (all `0.0` = neutral).

## 1.4. Training Data
| Dataset | Role | Size |
|---------|------|------|
| (Public) [BCCard/pii-masking-openpii-finance](https://huggingface.co/datasets/BCCard/pii-masking-openpii-finance) (v2) | Training / validation | ~58.5k train rows · ~14.5k validation rows |
| (Private) BCCard/pii-masking-openpii-finance-test (v2) | Golden Set (release gate; never used for training/tuning) | 2,000 rows (ko 1,460 / en 540) |

* Sources: curated Korean subset of `ai4privacy/pii-masking-openpii-1.5m` (label taxonomy remapped, name spans merged & naturalized) + finance-domain synthetic templates + **~30% English replay** (forgetting guard)
* Hard-example design baked into v2: surface-similar non-PII decoys (FP suppression), label-confusion pairs in one sentence (RRN↔FRN, DRIVER_LICENSE↔GENERIC_ID), weak-context true PII (FN suppression), long-span address boundary variants
* All values are synthetic; validity-pattern collisions with real identifiers are removed at generation time (e.g. card numbers are forced to fail Luhn)

## 1.5. Training Procedure
| Item | Value |
|------|-------|
| Method | Full fine-tuning (1.4B params — experts and router included) |
| Head | 33-class base head → 73-class head, initialized by copying base rows via taxonomy mapping |
| Loss | Token-level cross-entropy |
| Batch | effective 16 (per-device × world × accum), fixed across hardware layouts |
| LR / scheduler | 1e-4 / linear decay, warmup 3% |
| Optimizer | AdamW (fused), weight decay 0.0, max_grad_norm 1.0 |
| Epochs | 5 — best checkpoint by validation span micro-F1, **decoded with the same constrained Viterbi as deployment** |
| Precision | FP32 master weights + BF16 autocast; MoE router/experts explicitly kept FP32 during compute |
| Hardware | 1× NVIDIA H100 (~5h) |

<div align="center">
  <img src="figures/evaluation-train-1-1.png" alt="Training loss, learning-rate and gradient-norm curves for the v1 and v2 models" >
</div>

<div align="center">
  <img src="figures/evaluation-test-1-1.png" alt="Training-time validation metric curves for the v1 and v2 models" >
</div>

<br>

# 2. Evaluation
## 2.1. Setup
* **Golden Set**: independently generated 2,000-row test set (ko 1,460 / en 540), **adversarially hardened** — weak-context PII, decoys, confusion pairs and boundary variants are deliberately over-represented, so scores here read *lower* than typical in-distribution synthetic benchmarks
* **Protocol**: strict exact-match span P/R/F1 (CoNLL-style; boundary and label must both match) + **masking coverage** (share of gold PII *characters* covered by predicted spans, label-agnostic — the leakage-oriented metric)
* **Decoding**: constrained Viterbi + whitespace refinement — identical to the deployment chain

## 2.2. Results
### `validation` dataset

| Metric | v2 model / v2 validation |
|---|---:|
| micro F1 | 0.9599 |
| macro F1 | 0.9603 |
| ko strict micro F1 | 0.9562 |
| ko macro F1 | 0.9568 |
| en strict micro F1 | 0.9688 |
| en macro F1 | 0.9631 |
| **masking coverage** | **0.9979** |
| **ko masking coverage** | **0.9987** |
| **en masking coverage** | **0.9965** |

* These values were measured post-hoc by running the exported `final-bf16` artifact over all 14,543 v2 validation rows (ko 10,460 / en 4,083) through the deployment-equivalent chain: constrained Viterbi, actual tokenizer character offsets and whitespace refinement.
* Overall micro F1 and masking coverage pool all ko/en spans or characters before scoring. Overall macro F1 pools per-label TP/FP/FN across both languages and then averages the 18 label F1 values.
* Character coverage counts are ko **482,861 / 483,488** and en **264,979 / 265,898** gold PII characters.
* The training-time checkpoint-selection metrics remain ko micro F1 **0.9820**, en micro F1 **0.9739** and global macro F1 **0.9764** at epoch 5. They compare entity spans on token indices, so they are not interchangeable with the character-span values above and do not include masking coverage.

### `test` dataset
Independently generated Golden Set — deliberately harder than validation: weak-context PII, surface-similar decoys, label-confusion pairs and long-span boundary variants are over-represented.
**Δ = vs. the post-hoc validation baseline above** using the same `final-bf16` artifact and character-span evaluation chain. The difference measures test hardening and distribution shift, not model regression.

| Metric | v2 model / v2 test | Δ |
|---|---:|---:|
| micro F1 | 0.9336 | -2.63%p |
| macro F1 | 0.9308 | -2.94%p |
| ko strict micro F1 | 0.9441 | -1.21%p |
| ko macro F1 | 0.9416 | -1.53%p |
| en strict micro F1 | 0.9065 | -6.24%p |
| en macro F1 | 0.9017 | -6.14%p |
| **masking coverage** | **0.9964** | -0.16%p |
| **ko masking coverage** | **0.9956** | -0.31%p |
| **en masking coverage** | **0.9984** | +0.18%p |

* **Masking coverage stays ≥0.9956 on the adversarial set** — only 0.44% (ko) / 0.16% (en) of gold PII characters are uncovered; most strict-F1 losses are boundary or label-name errors, not leaks
* **English ADDRESS holds on hard boundary variants**: strict recall **0.983** on long-span address forms (state suffixes, unit/floor tails) that are heavily represented in this set
* **Weak-context person names are the main remaining leak channel**: ko `PERSON` strict recall 0.875 with 82 full-span misses (see Limitations)
* Label-swap errors (e.g. en `ACCOUNT_NUMBER` predicted as `GENERIC_ID`/`CARD_NUMBER`) keep **coverage 1.0** — the value is still masked; only the label name is wrong

## 2.3. Reading the numbers
Strict exact-match span-F1 on an adversarial test is a deliberately harsh score: a one-character boundary miss or a swapped label counts as a full error. For the product question — *"how much PII text leaks through?"* — masking coverage is the operative metric: **0.44% (ko) / 0.16% (en) of gold PII characters uncovered**, concentrated in weak-context person names.

<br>

## 2.4. Limitations
* **One layer of defense** — inherits the base model's positioning: not an anonymization or compliance guarantee. Deploy behind a regex backstop for fully structured identifiers (RRN patterns, card numbers, phones) and combine with policy-level controls.
* **Weak-context person names** — Korean names without honorifics/particles or list-form values are the main miss channel (ko `PERSON` recall 0.875 on the adversarial set). Consider a recall-leaning Viterbi operating point in high-sensitivity deployments.
* **Alphanumeric ID confusion** — `USER_ID`/`SECRET`/`GENERIC_ID`/`ACCOUNT_NUMBER` share surface forms; without cue words the label may swap (masking still applies — coverage stays ~1.0).
* **Synthetic-only training & evaluation** — no real customer text was used or evaluated. Real-world robustness (typos, slang, OCR noise) is unvalidated; shadow-mode rollout is recommended before enforcement.
* **Fixed label policy** — the 18-label taxonomy is baked in at fine-tuning time; changing masking policy granularity requires re-fine-tuning (runtime keep/mask toggles must operate on these labels).
* **Context window** — banded attention limits each token's context to ±128 tokens; trained sequence regime is ≤768 tokens (chunk longer documents).

<br>

# 3. Future Work
* **v3 data** — weak-context person-name hard positives, cue-word diversification for the alphanumeric ID group, privacy-safe failure-collection loop from shadow operation
* **Operating point** - recall-leaning Viterbi transition biases tuned on validation or a dedicated calibration set without Golden Set feedback
* **Serving** - target-hardware latency, throughput and memory benchmarks for the separately published INT8 weight-only ONNX artifact

<br>

# 4. Meta Info
## 4.1. Citation
```bibtex
@misc{bccard2026moaiprivacyfilter,
  title        = {MoAI-Privacy-Filter: A Korean Finance-Domain PII Detection Model},
  author       = {BC Card AX Team},
  year         = {2026},
  howpublished = {https://huggingface.co/BCCard/MoAI-Privacy-Filter},
  note         = {Full fine-tune of openai/privacy-filter for Korean/English PII masking in the BC Card domain}
}
```

## 4.2. See Also
* **Base model**: [`openai/privacy-filter`](https://huggingface.co/openai/privacy-filter)
* **INT8 ONNX artifact**: [`BCCard/MoAI-Privacy-Filter-INT8`](https://huggingface.co/BCCard/MoAI-Privacy-Filter-INT8)
* **Training dataset**: [`BCCard/pii-masking-openpii-finance`](https://huggingface.co/datasets/BCCard/pii-masking-openpii-finance)
* **Source data attribution**: `ai4privacy/pii-masking-openpii-1.5m` (CC-BY-4.0)

<br>