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wexumin/
overflow_probe_pisco_squad

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Overflow Probe on PISCO representations

A binary MLP probe that detects token overflow in soft-compressed document representations PISCO. Token overflow occurs when a document's information content exceeds the capacity of the compressed token budget, leading to degraded downstream QA performance.

How It Works

The probe takes a 4096-dim vector:

Component	Description
`mid_q`	Last hidden representation from mid layer (16) of a PISCO decoder model with standard prompt, compressed context, and a question.

Output: probability that the compressed representation has overflowed (i.e., lost critical information).

Installation

pip install torch huggingface_hub

Usage

1. Get the class definition

The model requires the PISCOClassifier class to load. Grab it from this repo:

python

from huggingface_hub import hf_hub_download
import importlib.util, sys

path = hf_hub_download("wexumin/overflow_probe_pisco_squad", "pisco_clf.py")
spec = importlib.util.spec_from_file_location("pisco_clf", path)
mod = importlib.util.module_from_spec(spec)
spec.loader.exec_module(mod)
PISCOClassifier = mod.PISCOClassifier

2. Load the model

model = PISCOClassifier.from_pretrained("wexumin/overflow_probe_pisco_squad")

3. Run inference

python

# postproj: compressed doc embedding (4096-dim)
x = mid_q

probs = model.predict_proba(x)  # (n, ) — is overflow probability
preds = model.predict(x)        # (n,)   — binary 0/1 (one can provide custom threshold parameter)

Training Data

SQuAD — extractive QA over Wikipedia paragraphs

Each context in the dataset was reduced to just question-answering sentence and then filled with noise context to be up to 128 tokens (in terms of pisco encoder tokenzier).

Architecture

→ Linear(4096, 512)
→ LayerNorm
→ GELU
→ Dropout(0.3)
→ Linear(512, 128)
→ GELU
→ Dropout(0.2)
→ Linear(128, 1)

Citation

bibtex

@inproceedings{belikova-etal-2026-detecting,
    title = "Detecting Overflow in Compressed Token Representations for Retrieval-Augmented Generation",
    author = "Belikova, Julia  and Rozhevskii, Danila  and Svirin, Dennis  and Polev, Konstantin  and Panchenko, Alexander",
    editor = "Baez Santamaria, Selene  and Somayajula, Sai Ashish  and Yamaguchi, Atsuki",
    booktitle = "Proceedings of the 19th Conference of the {E}uropean Chapter of the {A}ssociation for {C}omputational {L}inguistics (Volume 4: Student Research Workshop)",
    month = mar,
    year = "2026",
    address = "Rabat, Morocco",
    publisher = "Association for Computational Linguistics",
    url = "https://aclanthology.org/2026.eacl-srw.59/",
    pages = "797--810",
    ISBN = "979-8-89176-383-8"
}