LIQIIIII/Jeva-4B

Jeva: System One Models from First Principles

Qi Li · Xinchao Wang
National University of Singapore

Project Page · GitHub

Overview

Jeva-4B is a System One model for fast, direct decision-making over text. It selects among alternatives, assesses whether a statement is true, and assigns scores according to a rubric—without generating lengthy explanations.

Jeva is built around a simple idea: a decision model should respect the structure of the decision itself. The order of the options should not determine the answer, more options should not require a different model, and choosing nothing should be possible when nothing fits. Familiar options should also remain useful across new requests.

Four Defining Properties

• Null-aware. Supports an explicit “none of the above” outcome when no candidate applies.
• Permutation-invariant. Designed to preserve decisions when the same candidates are reordered.
• Option-scalable. Accommodates both small and large candidate sets within the same model.
• Cacheable. Reuses previously processed options across new requests, including new combinations of familiar options.

Reuse the options. Recompute the decision.

What You Can Do with Jeva

Capability	Purpose	Example question
Choice	Select a candidate, with an optional “none of the above” outcome.	Which team should handle this request?
Noul	Estimate the probability that a statement is true.	Does this report describe an ongoing service outage?
Score	Produce a numerical assessment using a supplied rubric.	How severe is the reported customer impact?

These capabilities support request routing, document selection, relevance assessment, and rubric-based evaluation. The same familiar alternatives can be used across different questions without reusing an earlier answer.

Explore Jeva

• Project Page: Discover the work, illustrations, and research findings.
• GitHub Repository: Find usage examples and guidance for running Jeva with your own tasks.
• Questions and Feedback: Share questions, report issues, or suggest improvements.

Intended Use

Jeva is intended for research and decision-support applications. Evaluate its suitability for your task and retain human oversight for consequential decisions.

Acknowledgment

If Jeva contributes to your work, please cite our work:

@article{li2026jeva,
  title={Jeva: System One Models from First Principles},
  author={Li, Qi and Wang, Xinchao},
  journal={arXiv preprint arXiv:2610.18773},
  year={2026}
}