{
  "id": "system-one-model",
  "code": "PTL-0224",
  "term": "System One Model",
  "aliases": [
    "decision model",
    "System One"
  ],
  "category": "foundations",
  "definition": "A System One model is a kind of AI model, named by TypeSafe AI in 2026, that returns typed, probabilistic decisions matching an output structure defined in advance, such as a label, score or branch choice with a confidence value, instead of generating free text token by token.",
  "description": "TypeSafe introduced the term in September 2026 with its first such model, Jev, describing the class as built for fast, structured decisions that software can use directly, such as classifying, routing, scoring, extracting and branching. The possible outputs are declared as types, all fields are produced in a single parallel pass, and each answer carries calibrated probabilities. This differs from structured outputs, where a generative language model's text is constrained to a schema. The vendor states that the model cannot hallucinate and that type errors are impossible, but also notes that its zero-hallucination figure follows from guaranteed schema matching rather than measurement. As of October 2026 the performance figures are vendor-reported and had not been independently reproduced.",
  "example": null,
  "broader": [],
  "narrower": [],
  "related": [
    "structured-outputs",
    "confidence-calibration",
    "routing",
    "hallucination",
    "large-language-model"
  ],
  "introduced": 2026,
  "added": "2026-10-27",
  "sources": [
    {
      "title": "Introducing System One Models & Jev",
      "authors": "Almeida (TypeSafe)",
      "year": 2026,
      "url": "https://typesafe.ai/blog/introducing-system-one-models-and-jev"
    },
    {
      "title": "Jev: TypeSafe's System One Model That Never Hallucinates",
      "authors": "Crabtree (DataCamp)",
      "year": 2026,
      "url": "https://www.datacamp.com/blog/system-one-models-jev"
    }
  ],
  "url": "https://protologue.com/t/system-one-model/",
  "citation": "Protologue. (2026). System One Model. In Protologue: A Taxonomy of Prompting and LLM Techniques (v1.4.0, PTL-0224). https://protologue.com/t/system-one-model/"
}