Interview, fail at interviews, learn from there where you need to improve, repeat until hired. Once hired, level up. There is no speed limit (https://sive.rs/kimo). Your experience at a YC startup as an early engineer would potentially provide you with the expertise and network to eventually move to another org or become a founder yourself (bootstrap or VC funding, depending on your objectives).

You could also apply for https://events.ycombinator.com/ai-sus and https://www.ycombinator.com/apply/

Wishing you the best of luck.

https://www.ycombinator.com/companies/industry/generative-ai

https://news.ycombinator.com/jobs

(no affiliation with YC)