Their docs at https://docs.typesafe.ai/confidence state "confidence is a statistic computed from the probability distribution the answer already gives you. TypeSafe computes it for you"

And further down "TypeSafe computes confidence from how the probability is spread across the options. All of it on one option gives 1.0; the more evenly it spreads, the lower the confidence. This demo uses (3 × largest probability − 1) / 2 to approximate confidence for three options."

So while we don't know the exact formula they use, it is just a function over the probabilities

I am open to the argument that this does not work well if you just plug in a qwen model instead of a model that is trained to output more statistically useful token distributions