Jev is now natively available in Yappy: computer use on your Mac at decision speed.
Yappy is a computer-use agent for Mac. You say what you want, it does it in the apps you already have. On the Yappy plan, every step of a task now runs through Jev, TypeSafe's System One decision model: the click, the field, the scroll are chosen in a few hundred milliseconds for a fraction of a cent, and the full model is only called when a step needs words.
Free download · Apple Silicon · macOS 13+
The same job application, filled two ways
One run per column, 18 September 2026, same Ashby form, same answers, same "do not submit". Jev's five decisions took 275 to 690 ms each and cost $0.003 in total. Method, caveats and sources: the full study.
Jev is a decision model, not a chat model
Jev is the first of TypeSafe's System One models. It does not generate text. It takes a description of your software's state plus typed questions, and returns typed answers: a choice from options you define with a probability per option, a yes/no probability, or a score along levels you name. TypeSafe quotes 70 to 500 milliseconds end to end, against seconds to minutes for a frontier chat model, at $0.042 per million input tokens with output free. It is served on OpenRouter as typesafe/jev-1.13 with a 32k context, and it reads text only.
That shape fits a GUI task almost exactly. Most of an agent's turn is not writing; it is deciding which control to act on next. A chat model narrates that decision at a few seconds per step. Jev returns it in one round-trip.
One typed question per step, no screenshots
- Snapshot. Yappy reads the front window through macOS accessibility as an indexed table of controls: role, label, value, position, reading order. Text, not pixels. Nothing is drawn, captured, or uploaded as an image.
- One call. The table and the goal go to Jev with one operation question (click, type, press Enter, scroll, wait, done, blocked) and one target question per operation over the controls that operation can legally touch. Only the head the chosen operation names is read.
- Validate, then act. The answer is checked against the offered options before anything moves. A malformed or low-confidence answer executes nothing. When the step is type, a small chat model supplies the text; Jev never produces prose.
- Hand off. No readable window, confidence under 0.25, three actions that changed nothing, or a field with no known value: the full agent takes over the same session with a note of what was already done.
The lane is on by default for every Yappy-plan session and costs nothing extra. To turn it off, set "fastLane": false in ~/.yappy/config.json.
| Step | Who decides | What is sent | Typical time |
|---|---|---|---|
| Which control, which operation | Jev | Window control table + goal | 275 to 690 ms measured |
| Text to type into a field | A chat model | The field and the goal | Seconds |
| Anything Jev is not confident about | The full agent | Same session, actions so far | As before |
Jev in Yappy, answered
What is Jev?
Jev is a decision model from TypeSafe, the first of its System One models. Instead of generating text, it takes a description of your software's state plus a typed question and returns a typed answer with a probability attached: a choice from options you define, a yes/no probability, or a score. TypeSafe quotes 70 to 500 milliseconds end to end and $0.042 per million input tokens, with output free. It is served through OpenRouter as typesafe/jev-1.13.
Is Jev a large language model?
No. Jev writes no prose, so it cannot run an agent turn on its own. What it can do is pick the next operation and target on a window faster and cheaper than a chat model can narrate one. In Yappy, a chat model is only called when a step needs words, such as the text to type into a field.
Does Yappy send screenshots to Jev?
No. Yappy reads the front window through macOS accessibility as a text table of controls: role, label, value, and position. That table is the state Jev decides over. No image of your screen is sent to Jev.
How fast is computer use with Jev in Yappy?
In our measured run on 18 September 2026, each Jev decision took between 275 and 690 milliseconds, and five decisions together cost $0.003. The whole job application took 1 minute 54 seconds end to end, against 13 minutes 14 seconds for the competitor on the same form. One run per column; the full method and caveats are on the research page.
How do I use Jev on a Mac?
Download Yappy, sign in, and choose the Yappy plan. The Jev lane is on by default for every plan session, so any task you give the agent runs through it. To turn it off, set "fastLane": false in ~/.yappy/config.json. Yappy needs macOS 13 or later on Apple Silicon.
Does Jev cost extra in Yappy?
No. Jev calls are billed to the Yappy plan like the rest of the agent's inference. There is nothing to configure and no separate key.
What happens when Jev is not sure?
It hands off. If there is no readable front window, confidence falls below 0.25, three actions in a row change nothing, or a field needs a value the task did not give, the full agent takes over the same session with a note of what was already done. You never wait on a stuck decision.
Free download · Apple Silicon · macOS 13+ · Yappy plan pricing