[psyklic]

There are a number of possible ways to approach it. Based on the description, you seem justified in getting more than 50/50 equity. But it may not be as "late stage" as you imagine.

For example, your description is very product-focused. I wonder whether there are users/customers? Revenue? Product/market fit? If I were a potential co-founder, lacking these would indicate it is still very early/"risky". If these are not present even after 1-2 years of work, perhaps a co-founder is 100% necessary to accelerate its growth.

Another aspect is whether the co-founder (and yourself) will be paid a market salary via the "pre-seed". If so, that could justify less equity. Or the opposite -- if you're paid more, that could more palatably justify a more even split!

Ultimately, I would just be honest and upfront with your potential co-founder about it. As long as you are both on the same page and believe it's fair, that is what matters most.