If you haven’t heard this yet, you will.
What science has found in extensive studies is that a person living with HIV on antiretroviral therapy (ART) with an undetectable HIV viral load in their blood for at least six months has a effectively zero risk of transmitting HIV to a sexual partner. This means people living with HIV can feel confident that if they have an undetectable viral load and take their medications properly, they will not pass on HIV to sexual partners (Undetectable = Untransmittable U=U).
Needless to say, there are many questions, including is the risk 0% or 93-96% or ????
This FAQ (and the entire site) provides a good introduction to how we’ve gotten to Undetectable = Untransmittable and what the challenges still are.