In the T100 specific rules section at the end of the WT Competition Rules it explicitly says:

10.3. Specifically, the following items are not allowed:
a.) Bottles/hydration or any other insert located in the front of an athlete’s race suit.
b.) Any insert in an athlete’s calf sleeves.

I would have thought that if they had time to put that in to the T100 section (Feb 2024 update), then they'd have time to do it for the WT general rules? Or do they have more control over T100 as they likely dont need to consult individual countries' federations?

It looks like you've reached a similar conclusion to me - it's legal but risky in case an official doesn't know it's legal. I just have to weigh up if it's worth the risk (probably not). However, for me, I'm quite confident that the aero benefit was very large.


Maybe I'll ask a technical official at the briefing / transition on race day.