Four long interviews.

They will drag out. They try to talk about their Culture Code, which is good in theory.

However, they have grown to the point where they have the "Silicon Valley Elitist" mindset.

I'd take their Culture Code pitch with a large grain of salt.

For a Technical Deep Dive, they expect you to provide a 3+ page outline of a project that defines your experience.

Sounds great, but instead of reviewing and letting you know if it's what they want, they will waste your time interviewing.

They are looking for how your experience matches their perception of reality and 'scale'.

I would definitely try to get someone to vet your proposal before wasting your time.