September 23, 2026
3
min

How System One Models like Jev complement planning optimization

Tom Cools
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Over a year ago I wrote about cats riding crocodiles and playing the banjo, and used that as an excuse to explain why LLMs can't solve your planning problems. The short version: LLMs predict the next token, and "the next token" is not the same thing as "the optimal shift schedule for ten nurses across a week" or "the optimal routes 50 trucks need to drive to deliver 600 parcels".

I drew a picture of AI as a set of nested circles, with GenAI in the middle and our kind of AI, mathematical optimization, sitting in the outer ring people seem to forget exists.

The different layers of AI, Timefold fits into the outer layer of old-school AI.

With the recent introduction of Jev, I wanted to revisit that drawing.

A model that refuses to talk

If you haven't seen it yet, Jev comes from a startup called TypeSafe AI, founded by a former OpenAI researcher named Diogo Almeida. Jev's pitch is that it won't write you an email, a poem, or a paragraph explaining its reasoning. Then what does it do? Give it an input and a set of pre-defined options, and it hands back a choice, a score, or a yes or no, each with a calibrated probability attached.

"Decisions, not strings." - TypeSafe's tagline

They call it a System One Model, borrowing the term from Kahneman's fast, intuitive System 1 thinking. If you have never heard about this, the book is a pretty good read!

The world noticed. Top of Hacker News for a day, a launch post with millions of views, TypeSafe claiming their model is up to 193 times faster and 444 times cheaper than a comparison LLM on the tasks it's built for. Whether those exact numbers hold up under independent testing is still an open question, and I'd treat "444 times cheaper" the way I treat any number a company publishes about its own product: interesting but might just be fluffy marketing numbers.

Yet, I'm intrigued by Jev, because it matches my perspective about GenAI and the wider AI ecosystem.

Appending my initial image

For a while, I didn't have a cool new hip example for the Machine Learning circle in my diagram. Yes, you can train neural networks to recognize anything, but it always felt a bit "fuzzy". But Jev resolves this issue nicely.

Jev is absolutely Machine Learning. It's trained, it's probably transformer-based, and TypeSafe has a whole reinforcement learning process behind it (they call it RLCD, reinforcement learning for calibrated decisions). So it lives inside the ML circle, same as GenAI does.

But it's not GenAI. GenAI is generative, it produces novel (for some definition at least) content, token by token, and that's precisely the thing Jev does not do. It picks from a fixed menu of answers instead of writing a new sentence every time.

The different layers of AI, Timefold fits into the outer layer of old-school AI. System 1 Models belong to Machines Learning, not to GenAI.

Finally a new cool kid on the Machine Learning block!

AI can solve any problem, not just GenAI

I've been preaching for a while that I feel the industry is overly focused on GenAI and is ignoring very valuable technologies in the broader AI space. With Jev, that is made even clearer. Not everything should be solved with GenAI, use the right tool for the job.

But where does it fit when we're talking about planning optimization, sort of our thing at Timefold? I personally believe that, despite it may seem that it makes "decisions" the way planning optimization does, that is somewhat incorrect. It can't do complex planning optimization, but it is a good complement to a tool like Timefold.

A Timefold model wants clean, structured input. Which technician has which certification. How urgent this job is. How long that visit will take. In the real world, that data has much messier origins: a customer's email, a technician's scribbled note, an inbound ticket that says "urgent!!" three times. Somebody, or something, has to turn that mess into structure before a solution like Timefold's can do anything with it.

That "somebody" today is often a person doing manual triage, or an expensive LLM call burning tokens to generate a sentence nobody reads. That second option is exactly where Jev makes a difference. A decision model can sit upstream of a Field Service Routing model, for instance, and classify each incoming ticket (urgency: low, medium, high; skill required; SLA risk) in well under a second, much faster and cheaper than an LLM can. Jev decides what the ticket means. Timefold decides who goes where because of it.

curl $JEV_URL \
  -H "Content-Type: application/json" \
  -d '{
    "state": {
      "customer_type": "hospital",
      "equipment": "Commercial HVAC unit serving the east wing",
      "service_contract": "premium",
      "task": "The AC in the east wing stopped working this morning. Patients are uncomfortable."
    },
    "questions": {
      "urgency": {
        "type": "choice",
        "instructions": "How urgently does a field service technician need to handle this task?",
        "criteria": {
          "HIGH": "Safety risk, complete system outage, critical or vulnerable site (hospital, data center), or major business disruption. Dispatch immediately.",
          "MEDIUM": "Degraded performance or a partial failure that affects operations but has a workaround. Schedule within 24 to 48 hours.",
          "LOW": "Routine maintenance, cosmetic issues, inspections, or minor problems with no operational impact. Schedule at the next available slot."
        }
      }
    }
  }'

‍The code snippet above is an example call towards Jev, where a certain state is passed in, as well as the question we want it to answer. In this case, we want to extract the urgency of a task for a field service technician. In return, we get the confidence levels for each of the options. In this case, the answer is pretty clear and both the confidence level and the resulting urgency is high.

{
  "answers": {
    "decision": {
      "type": "choice",
      "choice": "HIGH",
      "probabilities": {
        "HIGH": 0.99,
        "MEDIUM": 0.01,
        "LOW": 0
      }
    }
  },
  "usage": {
    "inputTokens": 388,
    "outputTokens": 39,
    "totalTokens": 427
  },
  "confidence": {
    "decision": 0.99
  },
  "warnings": []
}

Yes, an LLM could do such a clarification as well… but much slower and much more expensive. It's just not the right tool for a task like this.

This doesn't mean that LLMs are completely out of the picture. When it comes to structuring data or reasoning, LLMs still reign supreme.

So in the end, nothing much has changed when it comes to planning optimization. The optimization still has to be the optimization, provably feasible, reproducible, defensible to a dispatcher who's going to ask why. But the road getting to a clear dataset just got a lot easier.

Brand shiny new, not fully settled

Jev is a week old as I write this and its announcement is still reverberating through the industry. We are all still searching where it is strong and where it falls flat. There is a lot of hype right now and most of what we know about it comes directly from TypeSafe themselves, so we must take their data with a grain of salt until it's been verified. Additionally, open source alternatives like Laya are already popping up, so it's going to be interesting times moving forward.

This might be a big dose of confirmation bias, but I love seeingmore forms of "intelligence" pop up that are part of the AI sphere, but are explicitly not GenAI. I still believe that AI can solve any problem… but it is so much more powerful if different forms of AI, Planning Optimization + System 1 Models + GenAI, get combined together.

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