In short, the YC "Standard Deal" [1] is $125k in return for 7% of the company using a post-money SAFE. How they get that 7% is a bit confusing... There is not a predetermined cap and/or discount on the SAFE? That is, without knowing the terms of the later priced round where the SAFE converts, what SAFE terms define a 7% equity stake?
[1] https://www.ycombinator.com/deal/