Jeva: Rethinking System One Models from First Principles

Jeva: Rethinking System One Models from First Principles Paper Code Project Many LLM requests need a compact decision rather than a text answer: choose a tool, route a support ticket, test a condition, or assign a rubric score. System one models return such typed decisions directly instead of generating a rationale. TypeSafe introduced the term with its commercial Jev model, echoing Kahneman’s fast, intuitive System 1. Open models of this kind often put the request and every candidate into one prompt and read the answer from answer-token logits or a task-specific head. The paper argues that this design underemphasizes four requirements: Null-aware: the model should tell “no option applies” apart from “unsure which option applies”. Permutation-invariant: reordering the options should not change the decision. Option-scalable: a larger candidate set should not require a new output space. Cacheable: computation over recurring options, such as a tool registry, should be reusable across…