The sporting criteria cited in this article (and used in more sports than just cycling) is 5 nanomoles per liter for trans women.
It is interesting they chose to express the measurement this way - it is a nice, small number. Dare I say inoffensive? But medical science usually expresses it as nanograms per deciliter.
For reference, a man with less than 300 nanograms per deciliter is considered to have low testosterone.
The normal range of testosterone for women is 8-60 nanograms per deciliter (although I have also seen a range of 15-70 quoted).
What is 5 nanomoles per liter, you may ask. Just so we can compare like with like.
5 nanomoles per liter is 144 nanograms per deciliter.
Yup, the acceptable level of testosterone for a transgender person competing in the female category is more than double what is considered normal for an adult human female.