CoCo-Decision-4B-Ko

Version 1.0.0 (2026-09-29) · Git tag v1.0.0 in this repository

CoCo-Decision-4B-Ko is a 4B-parameter bilingual (Korean / English) decision model. Given a situation and a typed question, it returns a probability distribution instead of free text:

Question type	Output
noul	probability that a yes/no statement holds
choice	probability for each of the listed options
score	probability for each point on an ordinal scale

It is a LoRA adapter on Qwen/Qwen3.5-4B (revision 851bf6e8). Probabilities are read from the option-label token logits of a single forward pass, so one decision costs one prefill and no generation.

Not affiliated with or endorsed by TypeSafe AI. "System One" and "Jev" are names used by TypeSafe AI; this model independently implements a compatible decision interface.

Intended use

• Front-line routing and gating in agent systems: intent routing, "is this answerable from the document", "does this response meet the request", escalation decisions
• Places where a threshold on a probability is more useful than a generated answer (for example, act automatically above 0.9, ask a human below it)

Out of scope: open-ended generation, factual question answering without a supplied context, and high-stakes decisions (medical, legal, credit, employment) without human review.

How to use

Quick start (transformers + PEFT)

Requirements: torch, transformers>=5.17, peft>=0.21, and bitsandbytes for 4-bit loading.

import torch
from peft import PeftModel
from transformers import AutoModelForCausalLM, AutoTokenizer, BitsAndBytesConfig

BASE, REVISION = "Qwen/Qwen3.5-4B", "851bf6e806efd8d0a36b00ddf55e13ccb7b8cd0a"

tokenizer = AutoTokenizer.from_pretrained(BASE, revision=REVISION)
model = AutoModelForCausalLM.from_pretrained(
    BASE, revision=REVISION, device_map="auto", dtype=torch.bfloat16,
    # 8 GB GPU: 4-bit base. Remove quantization_config for bf16 on a GPU with >= 12 GB.
    quantization_config=BitsAndBytesConfig(load_in_4bit=True, bnb_4bit_quant_type="nf4",
                                           bnb_4bit_compute_dtype=torch.bfloat16, bnb_4bit_use_double_quant=True),
)
model = PeftModel.from_pretrained(model, "corners-ai/CoCo-Decision-4B-Ko", revision="v1.0.0").eval()


def decide(state: str, question: str, options: dict[str, str]) -> dict[str, float]:
    """Return a probability for each option key."""
    letters = [chr(ord("A") + i) for i in range(len(options))]
    lines = ["State:", state, "", f"Question: {question}", "Options:"]
    lines += [f"{letter}. {key}: {text}" for letter, (key, text) in zip(letters, options.items())]
    lines.append("Answer with the letter only.")
    prompt = tokenizer.apply_chat_template(
        [{"role": "user", "content": "\n".join(lines)}], tokenize=False, add_generation_prompt=True
    ) + "Answer:"
    ids = tokenizer(prompt, return_tensors="pt", add_special_tokens=False).to(model.device)
    with torch.no_grad():
        logits = model(**ids).logits[0, -1]
    label_ids = [tokenizer.encode(" " + letter, add_special_tokens=False)[0] for letter in letters]
    probs = torch.softmax(logits[label_ids].float(), dim=-1).tolist()
    return dict(zip(options, probs))


print(decide(
    "Customer: I was charged twice for my order last week.",
    "Which team should handle this ticket?",
    {"billing": "payment, refund or invoice problems",
     "shipping": "delivery status or delays",
     "account": "login or profile problems"},
))
# {'billing': 0.986, 'shipping': 0.008, 'account': 0.006}  (4-bit, RTX 4060)

print(decide(
    "Refunds are available within 14 days of delivery. The order was delivered 20 days ago.",
    "Is the customer eligible for a refund?",
    {"yes": "The statement is true.", "no": "The statement is false."},
))
# {'yes': 0.064, 'no': 0.936}

Prompt format

The adapter was trained on exactly this input; deviations lower accuracy and calibration.

• User turn: State: + the situation, a blank line, Question: + the question, Options:, one line per option as <letter>. <key>: <description>, then Answer with the letter only.
• Apply the model's chat template with add_generation_prompt=True and append Answer:.
• Read the next-token logits of the letters with a leading space (" A", " B", ...) and softmax over those letters only.
• Yes/no questions are two options: yes: The statement is true. and no: The statement is false. (or your own descriptions of the true and false case).
• Ordinal scores are options 0, 1, 2, ... with one description per level.
• A structured situation can be passed as JSON text in State:.

Hardware: 12 GB of GPU memory in bf16 at a 4,096-token context, or 8 GB with the 4-bit base shown above (JevBench public accuracy 0.857 in 4-bit vs 0.870 in bf16).

Serving and evaluation (optional)

The model was built and evaluated with oh-my-jev (omj), an open-source toolkit that serves it behind a TypeSafe-compatible /v1/systemone endpoint and runs the benchmarks below.

git clone https://github.com/iamupd/oh-my-jev && cd oh-my-jev
uv sync --extra semif
uv run omj bench --model corners-ai/CoCo-Decision-4B-Ko --suite jevbench-public --view   # benchmark, report in the browser
uv run omj ui --target corners-ai/CoCo-Decision-4B-Ko --target Qwen/Qwen3.5-4B             # side-by-side playground vs the base model

Training

• Method: LoRA (r=16, alpha=32) on the attention and linear-attention projections, one epoch, context length 4,096 tokens
• Objective: cross-entropy restricted to the option-label tokens, plus a Brier-score term for calibration and a KL term to the base model on selected tasks to limit forgetting
• Data: a mixture of publicly available Korean and English datasets (intent classification, reading comprehension, natural-language inference, sentiment, reasoning and response-quality judgement) converted into the three question types; synthetic decisions whose labels are computed by code (rule engines, date and arithmetic calculations); and synthetic decisions labelled by an LLM teacher, kept only when repeated labelling agreed. No outputs from any commercial decision API were used.

Benchmark contamination statement

• No JevBench items (public or sealed) were used for training.
• Part of the synthetic data was designed after studying the task types in the JevBench public set (long policy documents, multi-step reasoning, date arithmetic). All synthetic text was written independently and checked to share no 8-gram with the public items. Scores on the JevBench public set may therefore overstate performance on unseen items of the same types.
• Model versions were selected on separate contamination-filtered holdout suites, not on JevBench.

Evaluation

Measured with omj bench in bf16 (2026-09). Jev 1.13 figures were measured through its public API on the same items. Brackets are 95% Wilson intervals for accuracy.

Suite	N	CoCo-Decision-4B-Ko accuracy	CoCo-Decision-4B-Ko ECE	Jev 1.13 accuracy	Jev 1.13 ECE
JevBench public	231	0.870 [0.821, 0.907]	0.070	0.853	0.040
MASSIVE ko-KR (test sample)	600	0.915 [0.890, 0.935]	0.023	0.831	0.076
MASSIVE en-US (test sample)	600	0.933 [0.910, 0.951]	0.030	0.856	0.075

• JevBench public: hard-tier accuracy 0.748; coverage at 5% risk 0.745 (Jev 1.13: 0.836).
• The JevBench accuracy difference to Jev 1.13 is within the 95% interval; it is not a statistically established lead.
• ECE: expected calibration error (15 bins; lower is better).

Limitations

• Calibration is weaker than Jev 1.13 on JevBench (ECE 0.070 vs 0.040); recalibrate (omj bench --fit-temperature) on your own data before relying on fixed thresholds.
• Long policy documents and date/number calculations remain the weakest JevBench task types (public set: 0.63 and 0.40 accuracy), and the model is overconfident on the latter.
• Korean and English only. Other languages are untested.

Versions

Version	Date	Notes
1.0.0	2026-09-29	First release. LoRA adapter on Qwen/Qwen3.5-4B @ 851bf6e8

Load a fixed version with hf download corners-ai/CoCo-Decision-4B-Ko --revision v1.0.0.

License

The adapter is released under Apache-2.0. The base model is subject to its own license (Qwen/Qwen3.5-4B).

Citation

@misc{cocodecision4bko2026,
  title  = {CoCo-Decision-4B-Ko: a calibrated bilingual decision model},
  version = {1.0.0},
  author = {{Corners AI}},
  year   = {2026},
  url    = {https://huggingface.co/corners-ai/CoCo-Decision-4B-Ko}
}