What is Jev?
Jev is TypeSafe’s System One decision model: send state + typed questions, get structured answers your code can branch on—illustrated with a support email, not a chat.
Jev is TypeSafe’s flagship System One model. You send a state (context your code already has) plus typed questions. You get structured answers—values and probability distributions—that your software can branch on, sort, and route with.
It is built for decisions software consumes, not for prose humans read.
A support-email picture
Imagine a desensitized support message: “Package still not here—can you check shipping?” Your app already knows the order status. Instead of asking a chat model to “handle this email,” you ask Jev a Choice over queues like shipping | refund | billing | other, then let code decide what happens next.
That is the System One shape: state in → typed judgment out → code owns effects.
What it is not
- Not a chat LLM. No conversational product surface.
- Not “JSON mode on an LLM.” You are not prompting a text generator and parsing. System One evaluates typed questions and returns typed results directly.
- Not a replacement for permissions, refunds, or CRM writes. Those stay in deterministic code and human process.
Sources
- TypeSafe Introduction — System One / Jev overview
- System One