This seems to have got a bit lost amongst recent news. Hopefully an end to cheats like Austin Killips (amongst others) taking women's prizes and prize money. Interestingly it is based on the United States Olympic and Paralympic Committee.
Women’s Category.
Pursuant to the requirements set out above, the Women’s Category is limited to individuals who meet the following definition of female:
“Female means a person belonging, at conception, to the sex that produces the large reproductive cell.”
For purposes of applying this requirement, an individual who was not identified as female at birth may not participate in the Women’s Category at any Competitive Event.
Men’s/Open Category.
Any individual, irrespective of sex assigned at birth, is permitted to compete in the Men’s/Open category at any Competitive Event, subject to the regulations specified in USA Cycling’s Rulebook.
There are concerns because enforcement will be based on participants "warranting" they are eligible (i.e. self-id), but that is also subject to challenge by USA Cycling. So we'll see. It comes into effect on 15 September 2025.
usacycling.org/about-us/governance/policy-vii-competition-category-policy