Explainers· Last updated 2026-09-21

Jev System One versus System Two reasoning

Jev System One versus System Two reasoning is an independent briefing for engineers. Intent: compare fast decisions with deliberation.

Related search language: System One and System Two decisions, TypeSafe Jev, Jev decision model, decision automation.

Official facts that apply

• Evaluation API documented by TypeSafe: POST https://api.typesafe.ai/v1/systemone.
• List aliases: GET https://api.typesafe.ai/v1/models.
• Question types: Choice, Score, and Noul. Mix them in one questions map.
• Public list price for jev-1.13 (confirm on the models page): $0.042 per million input tokens; output tokens are free.
• Choice and Score return confidence. Noul returns only noul (0–1).
• Jev does not generate replies, code, or reasoning text. Code owns control flow.

Jev System One versus System Two reasoning: context

Jev System One versus System Two reasoning sits in the System One loop: you assemble a state, ask typed questions, and let your code act on probabilities and (for Choice/Score) confidence. The reader intent here is to compare fast decisions with deliberation. Keep the judgment narrow. TypeSafe’s docs say a good question is a snap decision a knowledgeable person could make in a few seconds — not an open-ended analysis.

Jev System One versus System Two reasoning: inputs

Inputs are state (string, object, or array of text) and a questions map. English is the primary training language. Images, audio, and video are not accepted. Filter unrelated fields before you send them: jev-1.13 loses accuracy as distractors grow, and unused tokens still bill as input. Name fields in instructions with backtick paths when the state is structured.

Jev System One versus System Two reasoning: decision logic

Pick the primitive that matches the answer your code can consume: Choice for an unordered set (max 255 options), Score for an ordered rubric (2–10 levels), Noul for P(yes). System One and System Two decisions is a product decision you encode in instructions and criteria, then threshold in code. Do not treat a Noul of 0.5 as a “medium” score — it means yes and no are equally likely.

Jev System One versus System Two reasoning: implementation notes

Pin jev-1.13.0 (or the current versioned ID) if you tune thresholds; jev-latest can move. Log the response model, usage.input_tokens, and the full probabilities map. Official Python and JavaScript SDKs read TYPESAFE_API_KEY and retry rate limits. This site does not issue keys.

Disclaimer

This is an independent unofficial site and is not affiliated with TypeSafe AI; official documentation is available at https://docs.typesafe.ai.

Primary documentation: https://docs.typesafe.ai. Never treat jev.pro as TypeSafe official documentation. We do not sell, issue, or proxy API keys.