Shadowing Practice: What Is Jev? The AI Model That Doesn't Generate Text - Learn English Speaking with Video

all right i want to talk about jev jev's a new ai model from a startup called type safe

and it's a bit unusual because it's an ai model

that doesn't actually write any text it actually answers questions by picking from a list

and then giving a probability for each one of his answers

now type safe calls this a new type of ai model it's a system one model

which is a name borrowed from Daniel Kahneman in his book one of my favorites thinking fast

and slow Kahneman describes two modes of thinking human thinking

that is and the first of those modes is called system one thinking

and system one thinking is fast and automatic

so what's two times two you instantly know the answer is

four without having to really work it out in your head that's system one thinking the other type

of thinking is classified as system two thinking and that's slow

and deliberate so

if i ask you what's 17 times 24 well you're probably going to need to work through

that one step by step to figure it out

or just look at the answer on your teleprompter

which is uh 408 there we go got it now most

of the ai models we use are built to write stuff

and a chatbot produces its answers one token at a time

in a ford pass now a reasoning model goes a bit further than

that and it actually writes out its chain of thought as we're going through this

so you can actually kind of see what it was thinking

which is basically as close to a system two model as ai gets

but but a lot of decisions inside software are not really system two they're just kind of quick judgment calls

so let me give you an example of that let's say

that we have got a email for customer support and

that email says that I was charged twice this month please fix it all right

so how do we respond to this email well the software

that's handling this email probably has to look at three types

of question one of the questions is is this a refund request yes

or no another question might be

which team needs to process this email maybe the billing team

or maybe it's the technical support team or maybe it's the sales team

and then also how urgent is this request how quickly do we need to respond

now a person just skimming an email like that they would instantly know

that refund yeah it's yes this is a refund request that's kind of a system one bit of work

and it's that kind of work that jev is built for

so a common way to automate a support email problem like

this today using an llm would be to send this email to the llm

and ask for the answers back the answers to these things in a structured format

so maybe we would go through this large language model output some tokens

and these tokens would represent a format maybe in json now

that mostly works

but it doesn't come back with a reliable sense of how

sure the model is how confident is a large language model

that it got the answer to these questions right well we could ask the model

but whatever it responds with wouldn't necessarily actually match the real

probabilities the model used to come up with this answer

but jev well jev does come up with probabilities so

if we send these questions to JEV we're going to get a very different looking response

so it takes in two things it takes in what's called state

which is the data the decision is about so

that might include our support email

that might include some recent customer charges as well all of

that is input into the JEV model

and it also takes in each of these questions as well into the model as input

and our three questions are actually three different types of questions so refund that is a yes

or no question

which type safe calls a null a team this team question it really comes down to a choice as to

which team is this so picking one option from a list

and then urgent

that really comes down to a score on a scale from

low to critical now all three of these questions go in in a single request

and whereas an llm would write its json answer out one token at a time jeff doesn't generate any text

so all three answers they all come back at once

and that's a big part of why this is so much faster

and cheaper than an llm on these types of questions now

we provide questions as input what is coming back i said

jeff doesn't give you text what it gives you coming back our probabilities as the output

so for refund it's going to be a single number let's

say it's going to come back with 0 .9 meaning there is a 90 chance that yes this is a

refund request for the team it's a probability for each one of the options that were part of this choice.

So for example, the billing choice, which is one of the three, may come back with a probability score of 0 .85.

And by the way, the answer to choice can only be the options that we give it.

So for team, it's always going to be billing or technical or sales.

And then urgency, well, that's going to come back if we kind of put this on a scale, pretty high to critical here so this is quite important.

Now, the model can still pick the wrong options or score any of these questions incorrectly,

of course, but the probability tells us how likely that is.

So how do you train a model to give accurate probabilities like this?

Well, let me go back to training traditional LLMs for a moment.

Most language models, they start with a stage known as pre -training.

So you pre -train a model first.

That means the model reads a huge amount of text and it learns to predict the next token.

Now that creates a model that knows a lot of stuff but it isn't much use to talk to yet.

So if we want to use this as a chatbot then we need to go to a second stage, which is called post -training.

Now, a lot of post -training uses a technique called reinforcement learning.

The model produces an answer, something scores that answer, and the model kind of gets nudged towards the answers that score well.

so the question is what's doing the scoring well one way to do that is with a technique called rl

hf reinforcement learning from human feedback

so people are doing the scoring there human raters look at two responses from the model

and they pick the one they like best

and those choices train a reward model and then

that chatbot is going to be trained to give answers

that the reward model scores highly people tend to like answers

that sound confident so an unfortunate side effect of rlhf is

that a model can learn to sound like really sure of itself even

when it's wrong

but that's just one form of reinforcement learning another form is r l v r that's reinforcement learning with verifiable rewards.

And the scoring here is automatic.

100

Did the model get the right answer to the math problem?

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Does the code it wrote pass its unit tests?

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Those sort of things.

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And that's a big reason that reasoning models today have got so good at math and coding.

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But the reward here only checks whether the final answer was right.

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It doesn't reward the model for knowing how sure it should be.

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And those models spend a

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while working through their chain of thought before they come up with an answer

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and that can make them a little bit slow and expensive to run.

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Now JEV is trained with a different form of reinforcement learning.

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It's called RLCD, reinforcement learning for calibrated decisions.

111

Now TypeSafe haven't published much about JEV's architecture

112

so i'll stick to what they have said well we know that jeff gives a probability

113

for each option and it's rewarded when those probabilities turn out to be right

114

so that's what the C is all about it's saying the model is calibrate it.

115

And a model that's calibrated kind of basically looks like this.

116

So along the bottom axis here if we map probability

117

and then along the side axis here we can map whether the model is correct.

118

So a well calibrated model is going to have kind of a diagonal line much like this.

119

So when we say that there is a 80 probability that 80 probability is going to be correct about 80

120

of the time that's calibration so back to the the refund question

121

that was the first of the three questions we posed to jeff about

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that support email so

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if we have probabilities we can use them to inform code using a threshold like this

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so we've got a probability threshold here one is certainty zero is definitely not kind of thing

125

so if a probability score is above let's say 0 .9

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so maybe our score comes back here somewhere

127

that means we can treat this support email as a legit refund request

128

and we can send that straight to the refund queue for processing

129

if however the score comes back anywhere kind of around between here and let's say 0 .1

130

well there's some uncertainty here so the code

131

that received a number like this would know to actually get a human involved

132

so now we need to bring in a person to actually check

133

that because we're not sure and

134

if a score comes in below 0 .1 well i think we can say that's not a refund request

135

so keep calm and carry on we don't need to do anything with that one because the numbers are calibrated,

136

the threshold also tells us roughly how often the automatic path will be wrong.

137

So the more a mistake is going to cost, the higher we would set the threshold.

138

Now this works for more than support emails of course.

139

Jeff can act as a guardrail

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that can be used around all sorts of things like around a chat bot that's checking messages going in

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and out for things like well jailbreak attempts

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but there are limits jev only takes text in as of today it's not very good at math

143

or even counting so you're going to want to leave

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that stuff to something else

145

and like any ai model it can be tricked by instructions hidden in the data it's reading

146

so is it time to throw away large language models

147

and replace them completely with system one models no hardly

148

but the two can work together so

149

if you think about a workflow maybe we have jev in the workflow

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that can make quick calls like sorting

151

that customer support email to see whether it's a refund or not

152

and then in the workflow we could go to a large

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language model to do the slower work work like replying to the customer

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and then we could go back to use Jev to classify any response

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that came back from the customer

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which is pretty much how Danny Kahneman said we work too

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most of what we do runs on those fast automatic system one processes

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so that's these two stages here and then the slow and careful system two, which is the large language model in this case,

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that only kicks in when something needs real thought.

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Oh, and I wanted to share a thing about the name of Jev as well.

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Jev is named after William Stanley Jevons, who was an economist who pointed out in 1865

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that as steam engines got more efficient britain actually used more coal that's known as jevons paradox

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so perhaps the same thing will happen with system one models

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when a judgment call is super fast

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and super cheap like with jev well it can go into places where an llm would be too slow

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or too expensive today like in every row of a database or on every line of a log file. Who knows?

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All right, that's Jev.

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Where would a System 1 model fit into the software that you work on?

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Let me know in the comments.

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Vocabulary and speaking notes for this lesson

This video has 169 sentences and 2101 words to shadow. The speech runs for 14:51. The speaker talks at a steady 141 words per minute, a comfortable pace for shadowing. 85% of the words are among the 3,000 most common in English; the rest is worth studying before you start.

Key vocabulary in this video

15 words from the video worth learning, with pronunciation and meaning:

Word	Pronunciation	Meaning
probability noun	/ˌpɹɑ.bəˈbɪl.ə.ti/	The state of being probable.
refund noun	/ɹɪˈfʌnd/	An amount of money returned.
reward noun	/ɹɪˈwɔɹd/	Something of value given in return for an act.
token noun	/ˈtoʊkən/	Something serving as an expression of something else.
automatic adjective	/ˌɔː.təˈmæt.ɪk/	Capable of operating without external control or intervention.
threshold noun	/ˈθɹɛʃ(h)oʊld/	The lowermost part of a doorway that one crosses to enter; a sill.
input noun	/ˈɪnpʊt/	The act or process of putting in; infusion.
mathematics noun	/mæθ(.ə)ˈmæt.ɪks/	An abstract representational system studying numbers, shapes, structures, quantitative change and relationships between them.
format noun	/ˈfɔːɹ.mæt/	The layout of a publication or document.
technique noun	/tɛkˈniːk/	The practical aspects of a given art, occupation etc.; formal requirements.
output noun	/ˈaʊtpʊt/	Production; quantity produced, created, or completed.
judgment noun	/ˈd͡ʒʌd͡ʒ.mənt/	The act of judging.
instantly adverb	/ˈɪnstəntli/	At once; without delay.
urgent adjective	/ˈɜː.d͡ʒənt/	Requiring immediate attention.
axis noun	/ˈæksɪs/	An imaginary line around which an object spins (an axis of rotation) or is symmetrically arranged (an axis of symmetry).

Phrasal verbs you will hear

Word	Meaning
come back verb	To return to a place.
come up with verb	To manage to produce, deliver, or present (something) by inventing, creating, thinking of, or obtaining it.
come down to verb	To reach by moving down or reducing.
go back to verb	To stem from; to originate in.
go through verb	To travel from one end of something to the other.
work through verb	To get past a difficult or stressful situation by thinking or talking about it.
come back from verb	To become successful, confident or effective again after an injury, setback, failure, embarrassment, etc.
throw away verb	To discard (trash, garbage, or the like), to toss out, to put in the trash.

Grammar in this video

The structures the speaker uses most, with the exact words from the video:

Structure	In the video
Passive voice be + past participle — the focus is on what happens, not who does it	is called · is classified · are built
Relative clauses who / which + clause — extra information about a person or thing	choice, which is · stage, which is · two, which is
Present perfect have/has + past participle — a past action that still matters now	haven't published · have said

Pronunciation to watch

The speaker uses 17 contractions and reduced forms, such as doesn't, we're, you're. Say them the short way, as you hear them.

The “th” sounds: threshold /ˈθɹɛʃ(h)oʊld/, mathematics /mæθ(.ə)ˈmæt.ɪks/
The “sh” and “zh” sounds: threshold /ˈθɹɛʃ(h)oʊld/, unusual /ʌnˈjuːʒ(u)əl/, efficient /ɪˈfɪʃənt/, instruction /ɪnˈstɹʌkʃən/, calibration /ˌkæl.ɪˈbɹeɪ.ʃən/
Long words — get the stress right: probability /ˌpɹɑ.bəˈbɪl.ə.ti/, automatic /ˌɔː.təˈmæt.ɪk/, mathematics /mæθ(.ə)ˈmæt.ɪks/, necessarily /ˌnɛs.əˈsɛɹ.ə.li/, unusual /ʌnˈjuːʒ(u)əl/

How to practise with this video

Listen to the whole video once without speaking and note the words you do not know.
Shadow it sentence by sentence at normal speed, repeating each one until your rhythm matches the speaker.
Record yourself and compare with the original, paying attention to words like probability, refund, reward.

What is the Shadowing Technique?

Shadowing is a science-backed language learning technique originally developed for professional interpreter training and popularized by polyglot Dr. Alexander Arguelles. The method is simple but powerful: you listen to native English audio and immediately repeat it out loud — like a shadow following the speaker with just a 1–2 second delay. Unlike passive listening or grammar drills, shadowing forces your brain and mouth muscles to simultaneously process and reproduce real speech patterns. Research shows it significantly improves pronunciation accuracy, intonation, rhythm, connected speech, listening comprehension, and speaking fluency — making it one of the most effective methods for IELTS Speaking preparation and real-world English communication.

Shadowing technique: read the full step-by-step guide →

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Vocabulary and speaking notes for this lesson

Key vocabulary in this video

Phrasal verbs you will hear

Grammar in this video

Pronunciation to watch

How to practise with this video

What is the Shadowing Technique?