Open Alternative to Jev
An open-source Python package that produces typed, calibrated decisions from any open-weights language model in a single forward pass, reading the model's own next-token probabilities rather than generating text, as an open alternative to TypeSafe's Jev.
Open Alternative to Jev, imported as the package so1 for System One, answers a typed, multiple-choice-style question from a language model's next-token probability distribution at a single position, restricted to the offered options, rather than by generating free text. Running locally on a stock Qwen3.6-27B model, the project reports beating Jev 1.13.0 on a shared community benchmark of 400 cases and 2,000 typed decisions on accuracy, on how closely its probabilities match the benchmark's gold distribution, on calibration error, and on latency, all zero-shot with no training.
It also reports a packing mode for questions that share a passage of context: writing that shared state once instead of once per question cuts the tokens processed several times over and increases throughput at unchanged accuracy compared with asking one question per forward pass or batching several questions with padding. It is a library called in-process rather than a hosted API, and does not provide a drop-in replacement for Jev's own HTTP endpoint.
It runs on Hugging Face Transformers and vLLM and is licensed under Apache-2.0.