Is Jev open source?
No. Jev is a closed model, served from TypeSafe’s API, and the weights have not been published. What is open is everything that grew around it within a week: 34 projects in this directory train, adapt or replace a System One model you can run yourself.
Updated 22 Sept 2026 · by Made with Jev
In short
- Jev itself: closed weights, API only, $0.042 per million input tokens.
- The request shape is public, so an open clone that copies it works with the official SDKs. kev does exactly that.
- The open models are small — 151M to about 4B — because deciding is not generating. Laya is 421M and runs in about 1 GB.
- Accuracy is close, in each project’s own tests. Calibrated confidence is the part nobody has matched in public.
What is closed, and what is not
Jev is sold as an endpoint. TypeSafe’s models page lists the version, the price, the rate limits and the context window. There is no download and no self-hosting licence. That is the whole of the closed part.
The rest is documented in public: the request shape, the three question types, the response with its probabilities and confidence, and the SDKs that wrap them. That is why so many replacements exist and why most of them are API-compatible — if your code already sends a state and a set of typed questions, pointing it somewhere else is a change of base URL.
- Weights
- Not published by TypeSafe
- Licence to self-host
- None offered
- What is public
- The API, the SDKs and the docs. Quickstart
- Open alternatives here
- 34, across 4 families
- Fastest published local figure
- Under 15 ms a decision, on the same machine (von)
- Closest drop-in
- kev: TypeSafe's API shape, running on a MacBook
What each project claims
Every figure below is the project’s own, on a benchmark it chose. None has been re-run here, and at least one author says so himself: kev’s says plainly that kev was trained on the datasets he scored it against.
| Project | Built on | What it publishes |
|---|---|---|
| Laya | 421M, ~1 GB of inference memory | 86.5 decisions a second, P50 about 9 ms, running locally |
| kev | Qwen2.5-0.5B, LoRA and a head | 79.7% against Jev's 81.1% on the author's own suite; ~160 ms for six questions |
| OpenJev Verdict 2.0 | 151M, non-autoregressive | 77.10% accuracy, Brier 0.0636, ECE 0.0144 on its own set |
| von | Local, on your own machine | Under 15 ms a decision, because there is no network in the loop |
| NanoJev | 0.6B, with its training pipeline | The full distribution in one forward pass, no token decoding |
| QwenJev | Qwen-3.5-4B, a vision-language model | 0.169 s per frame, and it reads images, which Jev cannot |
| openjev-sglang | Qwen3.6-35B-A3B on SGLang | 64 tasks in under a second, reusing the prefill across questions |
| Simple Jev | Any Hugging Face model | In production at Featherless.ai; handles images too |
Models trained to do Jev's job
Small models, trained from scratch or adapted, that answer typed questions in one pass. This is the closest thing to an open Jev, and the sizes say how little the job needs: 151M to about 4B.

GitHubTools and apps
kev
A tiny Jev-like model on Qwen2.5-0.5B that trains and runs on a MacBook.
Jared Palmer
~160 msMD Fazal Mustafa
@the_mdfazal
🚨 A LOCAL 421M MODEL JUST ATE CLOUD JEV ON SPEED Laya is an open-source System 1 decision model that runs on your machine. Laya: 86.5 decisions/sec, P50 ~9ms, score 46 Jev: 3.2 decisions/sec, 317ms API round-trip, score 1 Ships with: — 421M params — ~1GB inference memory — Millisecond local calls, no network — Typed decisions in one forward pass — Apache-2.0 and self-hosted While the cloud waits, local decides.
Geek Lite
@QingQ77
复刻 Jev 的并行决策思路,让 0.6B 小模型一次前向直接输出完整概率分布,不做输出 token 解码。 github.com/TianyuCodings/…
151MSize · 77.10% accuracy
GitHubResearch and data
OpenJev Verdict 2.0
A 151M non-autoregressive decision engine, with its numbers published.
Heman10x

GitHubTools and apps
OpenJev (Verdict)
An open 151M decision model on ModernBERT, with a WebGPU playground.
Hemant Kumar
~26Stars
KaLM-Embedding
~7Stars
Kye Gomez
Vincent Wang-Maścianica
@vinnylarouge
I reverse-engineered a jev-like architecture given its type. You can find the repo here to train your own jevlikes: github.com/vinnylarouge/j…
GitHubResearch and data
jevlike
25Stars
SiliconLabAI
7Stars
Abhishek Rai
Adapters that make any model answer like Jev
No training at all. Restrict the next token to your options, read the candidate logits, and you have a typed decision with probabilities out of a model you already serve.
Eugene Cheah - AI builder @ 🇸🇬|🇺🇸
@picocreator
love jev, but upset it - isn't open source? - it lack vision capability? We fixed all of that, introducing SimpleJev.ai A fully open source library which takes any HF model and Jev-ify it, with an API endpoint Now on github, and live in production at @FeatherlessAI
GitHubTools and apps
Simple Jev
~9Stars
Nokia Applied Research

GitHubTools and apps
Open Alternative to Jev
Typed, calibrated decisions from any open-weights model, on your own GPU.
ikermoel
~16Stars
zhangcy122
Eric Zhang
@ekzhang1
Inspired by @typesafeai , here is a Jev-compatible public API to play with It runs a comparable open model (Qwen3.6-35B-A3B), and just uses SGLang radix cache to preserve the prefill reuse / really fast parallel systemone generation - 64 tasks in <1s. github.com/ekzhang/openje…
Nick Khami
@skeptrune
you can make any open source model behave like jev with just a bit of inference engineering. it's shockingly easy. to prove it, we built a new endpoint we're calling deepseek-v4.1-flash-jev. see the demo below. here's how it's done: sglang (an inference engine) offers a scoring endpoint in addition to the normal generation one. in scoring mode, given an input & set of possible answers, it forces the model to produce probabilities for each one. example: > input: what is most common letter in abcccde? > possible answers: a, b, c > output: (c, 0.9), (b, 0.0.5), (a, 0.05) getting the above behavior instead of streamed output is as simple as using sglang's /v1/score endpoint instead of /generate. there's just one other trick required. for deepseek, you have to add a closing think tag before the response. this forces a direct answer instead of a reasoning trace. if you want reasoning, you can do that too, but imo that makes things too slow to be worth it. dsv4.1 flash is not as good as jev, but if we had enough spare compute to experiment with this same approach for a larger model then i think the decision quality would be at least as good, if not better. also, somewhat unrelated, i think decision-making models kill all prospecting & sourcing work. i would have absolutely killed to have jev or similar when i was recruiting @mintlify. absolutely incredible.
XTools and apps
deepseek-v4.1-flash-jev
0.169 sPer frame
RJMSWD
alex nikolic
@justALEXWORTEGA
Typesafe: pnewed 💨 Jev: liberated 🫡 I trained an MLP on top of qwen 4b and it works literally like JEV huggingface.co/AlexWortega/op…
Live siteResearch and data
openjev on Qwen 4B
~4Stars
hwfengcs
~4Stars
Sung Kim
Anand Prasad
@theanandprasad
you can turn any low-cost open-source LLM into a Jev like fast decision model without training it. Here's how to do it: An LLM doesn't write text directly. At every step it scores every word in its vocabulary for how likely that word is to come next, and then it picks one. Those scores are called logits. Suppose you want to know whether a customer email is angry. The usual way is to ask the model, wait while it writes a paragraph, and then try to pull a yes or no out of the response. The trick is to never let it write anything. Give it the email content and the question, and end your prompt with "Answer:". Your full prompt will look something like this: [ Message: "Third time I've contacted you. Still broken." Is this customer angry? Answer yes or no only. Answer: ] The model reads the prompt once and scores every possible next word. You look at two of those scores. "yes" scores 8.1 "no" scores 5.9 Convert those two scores into probabilities and you get 90% yes and 10% no. (Use softmax function -- google it) Your code then uses that number directly. If it's above 0.8, escalate the ticket. Congrats, you have created your own Jev! Here’s why it works: 1. It's fast. Reading a prompt happens in one parallel pass. Writing is the slow part because the model writes one word at a time. Here the model never writes. 2. It's cheap. Output tokens are the expensive ones, and this produces none. 3. There's nothing to parse. You always get a fixed output, and never a paragraph. 4. You get a confidence level along with the answer. A 0.55 means the case should go to a human or a bigger model. A 0.98 means you can act on it. I tried running the code on llama 3.3 70b (via openrouter) and the accuracy was 21/22 (95%). Cost per query: $0.000013, latency: ~500ms
XResearch and data
Jev-like decisions from open LLMs
恒星sun
@vintcessun
如果分类结果最终要喂给业务系统,生成一段 JSON 往往不是最省事的路径。Simple Jev 把开放模型变成结构化决策接口。 https://github.com/featherless-ai/simple-jev 它复用共享上下文的 KV cache,只读取各问题候选标签的下一 token logits,再由服务端组装 choice、score 和真值判断。省掉逐 token 解码与 JSON 解析,多问题场景更有价值;common 目录还把提示契约和评分逻辑抽成可复用层。适合路由、审核、打分,但准确率与校准仍需按任务验证。
XResearch and data
Simple Jev, reusing the KV cache
Running it on your own machine
Where self-hosting actually pays: no network hop, no token bill, and nothing leaving the device. The fastest published figure here is under 15 milliseconds, which no API can match by definition.
<15 msLatency
wfzyx
~4Stars
afshinm
~3Stars
neko233-com
~18Stars
GitHubTools and apps
open-jev (browser TypeScript)
Typed decisions in the browser: one state, any number of options.
Nico Martin
生ビール
@wmoto_ai
ローカルTypesafe Jev、できたんやないか? もうちょい速度は改善余地ありそう
XResearch and data
A local Jev
Petru - Tech Driven
@techdrivenpetru
Yes but not with Jev. I used another classifier, locally, just as fast, just as good. Example: setup a "server" in python that loads the classifier model. Add a hook in Claude that fires on "pre-tool-use" and next time you ask Claude a random question like "how do I lint check a project?" and it tries to freelance and read your entire repo only to intoxicate itself and pollute its context, the classifier will slap its hand, say "no sir, you answer from knowledge" and deny the tool call. I tested this yesterday with success, but need to refine it as it misfires. Basically I was able to identify general queries, instances where I would ask something and Claude would rush ahead and run pip install without me asking or just write code instead of answering. A classifier is hypercheap compared to a regular LLM and would catch all of these. The model I used was DeBERT large. It's still stupid fast, I tested it on an Apple with M1 (regular) and you don't feel it running.
XResearch and data
A local classifier instead of Jev
Simplifying AI
@simplifyinAI
so we already have an open source alternative to jev... and it's 6-7x faster?! it's a typed-decision classification system: no chat, no generated text, just fast yes/no, scoring, or choice answers. > runs in under 1gb of memory > free on hugging face > runs on a laptop, or even a phone there's a real demo where it plays snake live, making a fresh decision every single move. two honest limits, straight from the project itself: > only 512-1,024 token context, some cases won't fit > weaker generalization than jev out of the box
XResearch and data
An open typed-decision classifier
~3Stars
Iron-LYK
Experiments at the edge of the idea
What happens when you push a decision model past what it is for. Two people built chat out of a model that cannot write; one project calibrates the questions themselves against your labels.
7Stars
GitHubResearch and data
ChatJev
Driving the classifier as a next-token predictor, one token at a time.
Erik Dunteman
26Stars
Kyle Pena
~31Stars
GitHubResearch and data
jev-calibrate
Tune your Jev questions against your own labels, then confirm on held-out data.
smkrv
Richelle🚢
@Richelle_Ji
Hosting a demo + hack night in SF showcasing the coolest projects built with Open-Weights Jev. Come see what’s possible, hack, or hang out. Reach out for an invite or get involved!
XTools and apps
An open-weights Jev demo night in SF
What self-hosting actually requires
Less hardware than people expect. These are classifiers: they read a state and emit a distribution over options you defined, with no decoding loop, so the models are two to three orders of magnitude smaller than the ones you would otherwise ask. Laya fits in about a gigabyte. kev trains and runs on a laptop. Verdict runs in a browser tab on WebGPU. openjev-sglang is the outlier, because it wraps a 35B model and buys its speed from the SGLang radix cache rather than from the model’s size.
What it costs you is the three things TypeSafe absorbs. One: batching, because the speed everyone quotes for Jev comes from answering every question against one prefill, and a naive local server answers them one at a time. Two: calibration, because a probability is only useful if 0.8 means 0.8, and that is trained, not configured. Three: keeping a GPU warm, which is the real comparison against $0.042 per million tokens.
What the open alternatives do and do not match
They match the interface. Typed answers, several questions in one pass, probabilities over a closed set: all reproduced, and in places extended — Simple Jev and QwenJev both read images, which Jev does not, and OmniJev pushes the same idea at multimodal robot input.
They do not yet match the confidence. Jev’s confidence score is the number the builds in this directory actually depend on: act automatically above a threshold, escalate below it. No alternative has published a calibration comparison run by anyone other than its own author. OpenJev Verdict 2.0’s Brier score of 0.0636 and expected calibration error of 0.0144 are the most anyone has shown, on their own set. Treat that as a reason to run your own test — jev-calibrate exists for exactly that — not as a substitution.
Watch one run
Two walkthroughs of the open side, by people who ran the models themselves rather than reading the READMEs.
Guideyoutube.com/@CoderOne
Open Source, Faster Jev is HERE
Coderone on Laya, the open System One model from Convai Innovations: what typed decisions are, why they replace a share of LLM calls, and Laya run locally to see if its figures hold up.
Guideyoutube.com/@samwitteveenai
Open Jev Models Are Here!!
Sam Witteveen goes through the open decision models released in Jev's first week.
If you want it cheap rather than local
Self-hosting is usually the wrong lever for cost. A median published run in this directory costs a fraction of a cent per decision, so the reasons to run your own are data residency, an offline device, a latency floor the network cannot meet, or a model you want to fine-tune on your own labels. The numbers are on the pricing page, the model itself is explained on what is Jev, and every repository in the directory is on the GitHub page.
Common questions
- Is Jev open source?
- No. TypeSafe serves Jev from its own API and publishes docs, prices and rate limits, not weights or a licence to run it yourself. Everything open about Jev today was built by other people.
- Are Jev's weights available?
- TypeSafe has not released them. Other people have trained their own decision models instead and published those: Laya at 421M parameters, NanoJev at 0.6B, OpenJev Verdict at 151M, kev on Qwen2.5-0.5B, and KaLM-Jev in three sizes.
- Can I run Jev locally?
- Not Jev itself, but a replacement, yes. von reports under 15 milliseconds a decision on the same machine. Laya runs in about a gigabyte of inference memory at 86.5 decisions a second. kev trains and runs on a MacBook and follows TypeSafe's API closely enough that the official SDK works against a local server.
- What is the best open-source alternative to Jev?
- It depends what you are replacing. For a drop-in local endpoint: kev, von or Laya. For a trained small model with published calibration: OpenJev Verdict 2.0 or NanoJev. For an open model you already serve, no training needed: Simple Jev, AnyJev or Open Alternative to Jev, all of which read the candidate logits instead.
- Do the open alternatives match Jev's calibration?
- Nobody has shown that they do. Accuracy is the number every project reports; calibrated confidence is the part Jev is built around, and the only public comparisons are each project's own, on datasets they chose. Test on your own labels before you trust a threshold.
- What is Laya?
- An open System 1 decision model, 421M parameters, that arrived within a week of Jev's launch. Its author reports 86.5 decisions a second at a P50 of about 9 milliseconds in roughly 1 GB of inference memory, and there are already Go and Apple-silicon ports of it.
Made with Jev is independent and not affiliated with TypeSafe AI. Every figure on this page is the one its author published, linked to where it can be checked.