People keep saying "well when it comes to it, they won't really let transmen compete in the women's categories, that would obviously not be fair"
The problem is that "fair" is subjective.
If an exploitative male has a testosterone reading below 10 nmol/L, he will be able to compete as a female.
The IOC have suggested that each sporting body retain the ability to evaluate on a case-by-case basis.
So Usain Bolt (extreme example, but let's go with it....) lowers his testosterone (who knows, he might already be within the threshold) and wants to compete as female. It will be patently obvious to everyone and anyone that even if his muscles get a bit smaller (and note: there is no requirement to do so; within 12 months on presumably a maintenance regime, not an "atrophy" regime), that he retains an unfair advantage.
So he wins. Easily. And the IAAF say "Oooh, hang on, that's not right, is it? I mean, I know we said all this about testosterone, but we didn't mean for this to happen". So they exclude Bolt from female competition because he has an unfair advantage. But they wouldn't exclude a 6'5'' born female for having the very same advantages as trans-Usain Bolt - height, long long legs, great muscle tone and a testosterone reading of 9.9 nmol/L. Usain Bolt would be excluded only because he is trans, and that will create a massive uproar.
The IOC may have cited a "get out clause" but their own recommendations - that testosterone is the only differentiator - means it can never be evoked.
The only way he could demonstrate that he doesn't retain an unfair advantage is by losing. And frankly, that's not a satisfactory outcome for trans athletes either, that only if they are shit will they be allowed to compete.