Put together some notes on Jev and the new category of system one aka decision models simonwillison.net/2026/Sep/21/je…↗

Have a question? Ask Jev AskJev.net↗

Jev is incredible. I'm scared people are using it wrong.↗

@jamesm If you ask your mom "is the sky blue" she says "yes" immediately, that's jev. If you ask your dad "why is the sky blue" he talks for ten minutes, that's an LLM.↗

Running Jev to see how fast it can remove negative comments from chat↗

when a designer gets access to Jev↗

I turned Jev into an image model…? Presenting Jevinci! github.com/achimala/jevin… The paintings are pure JS, no AI image-gen. Jev predicts every pixel's color in parallel and we paint them. The more confident Jev is in a prediction, the wider the brush. (sped up 4x)↗

Looking for inspiration on what you are able to do with Jev (by @typefaceai) this weekend? Built a website called Jevable (jevable.com) which showcases all the fun demos on X - filterable by a few categories. Feel free to add your own project by using the + button!↗

I've seen people describe Jev as an "AI if statement". But what if it actually WAS an if statement? Introducing Probably: a programming language powered by Jev: …bably-lang.southpolesteve.workers.dev Jev baked into the language. “feels” asks a question. “match” routes between d…↗

What is a decision model? Jev by @typesafeai answers yes/no and multiple-choice questions, with a confidence score. Much of software development are a sequence of decisions, and Jev is 10x cheaper and faster than an LLM. Let’s understand this through practical examples:↗

you can also use Jev to cut costs and token usage! make your agents more efficient by compacting shell and large file output before it reaches the LLM passing only necessary tokens to the model and carrying fewer tokens through the rest of the conversation↗

Jev is INSANE. 🤯 in 24.9 seconds it read 384 news from this morning and told 15 brands which stories to hop onto today, for $0.19. Claude Opus 5, running on the same feed at the same time, got through 4/384 and cost $0.77. per headline that is ~390x cheaper, and the answer co…↗

I’ve put a ton of tokens through Jev now, and...I have thoughts. 1. The big labs lost the script TypeSafe’s intro video says, “We’re building prod, not God” — and can I just say? Hell yeah. @typesafeai built something for engineers like me, so I can build products for people li…↗

I built a voice controlled computer-use for my mac using @typesafeai's Jev and it's INSANE how fast it is! I can dictate "open the notes app and create..." and the app opens before I even finish my sentence.↗

JEV is INSANE. We gave it 3 million replay events In 40 seconds, it watched 3,247 sessions, caught 132 rage clicks, 116 dead clicks and 95 JavaScript errors, and opened 213 draft PRs to fix them. All for just $2.17. JEV can also flag abandoned forms, rank every issue by sever…↗

Building a Harness with Jev Agents run in a loop: an LLM decides what to do, a tool executes, a model evaluates the results, and then continues in that loop until the task is complete. Agents and LLMs were initially difficult to integrate into software applications, which depen…↗

New experiment: json-render + jev The future Generative UI is instant Your components, your actions, your design system Rendered in milliseconds↗

Built a tax document classifier with Jev. We ingest thousands of tax documents using an LLM pipeline I built last tax season. I read multiple articles as late as April this year claiming AI fails at tax document classification. Wasn't the case back then, and it's proved wrong a…↗

Jev is the future↗

Just trying out Jev, I made a Chrome extension that: - Listens to your YouTube audio (optional) - Detects if it gets to a sponsor segment - Skips it ➡️➡️➡️ - All in real-time while costing ~$0.005 per video Prototype project, BYOK, open-source: github.com/trungdq88/yout…↗

I turned my best X posts into an automated blog and newsletter powered by @jessethanley's new tool X is basically my CMS right now. So far the open and click rate is better than SES and the technical setup was significantly easier. I just gave my clanker the MCP and it did ever…↗

I gave Jev 3,282 of my X posts across 100M views and asked it to find what actually works for growth. 4,252,330 tokens $0.1282 for the full 8m 34s run! Each post got 8 questions about the topic, hook, tone, whether it teaches something, etc. How-to posts got 150 median likes v…↗

i had jev analyze over 10,000 hacker news comments. 43% of them were correcting someone. ☠️ hnmoodring.neato.fun↗

introducing Unclutter: a smart ad + slop blocker with Jev 🤓 it auto cleans up pages from slop elements: ⬖ ads ⬖ cookie banners ⬖ upsells ⬖ bs dialogs BYOK. open source + free, download below 👇↗

All the grifters are completely wrong about Jev’s architecture so I decided I’d release an open-weight version. BUT training takes time, so while we all wait I decided I’d drop the sauce. archerhume.com/posts/jevs-arc…↗

rebuilt the X algorithm with Jev - uses real weights - simulates virality of your post - has a global feed (you see everyone) it's insanely accurate↗

After co-inventing ChatGPT, I kept asking myself: why have superhuman chat models not led to AGI? I’ve spent the last 2 years in stealth building a new way to train models (RLCD), and a new type of frontier AI model that we are releasing today: Jev • 20-200x faster • 40-400x ch…↗