---
title: "Jev in Yappy — computer use on your Mac with TypeSafe's Jev decision model"
description: "Jev, TypeSafe's System One decision model, is natively available in Yappy, the computer-use agent for Mac. Each step of a task is decided in a few hundred milliseconds for a fraction of a cent, with no screenshots."
canonical: "https://yappy.biz/jev/"
last-updated: "2026-09-19"
---

# Jev is now natively available in Yappy

Yappy is a computer-use agent for macOS. You say what you want and 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.

- Available: Yappy 0.4.60 and later. Download: https://yappy.biz/api/v1/releases/latest
- Requires: macOS 13 or later, Apple Silicon.
- Where it runs: the Yappy plan, on by default. `"fastLane": false` in `~/.yappy/config.json` turns it off.
- Screenshots sent to Jev: none. Jev reads a text table of the window's controls.

## Measured

Same job application, same answers, same "do not submit", one run per column,
18 September 2026. Full method, caveats and sources:
https://yappy.biz/research/yappy-vs-heyclicky/

| Measure | Competitor | Yappy + Jev |
|---|---|---|
| End-to-end time | 13m 14s | 1m 54s |
| Actions taken | ~104 | 22 (5 chosen by Jev) |
| Input tokens | 11.24M | 0.39M (0.07M of it Jev) |
| Estimated cost, same rate card | ~$4.24 | ~$0.24 |

Jev's five decisions took 275 to 690 ms each and cost $0.003 in total.

## What Jev is

Jev is the first of TypeSafe's System One models. It does not generate text. It
takes a description of software 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 named levels. TypeSafe quotes 70 to 500 ms
end to end 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 reads text only.

Sources: https://typesafe.ai/blog/introducing-system-one-models-and-jev and
https://openrouter.ai/typesafe/jev-1.13

## What Yappy does with it

1. **Snapshot.** Yappy reads the front window through macOS accessibility as an indexed table of controls (role, label, value, position). Text, not pixels.
2. **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 it can legally touch.
3. **Validate, then act.** The answer is checked against the offered options before anything moves. When the step is *type*, a small chat model supplies the text; Jev never produces prose.
4. **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.

## Questions

### 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.

## Links

- Download Yappy: https://yappy.biz/
- The study behind the numbers: https://yappy.biz/research/yappy-vs-heyclicky/
- Pricing: https://yappy.biz/pricing/
- Machine index: https://yappy.biz/llms.txt