They have published a bunch of stuff about their internal tools in the past. Look up https://stripe.com/blog/stripe-home and compare it to this, as an example.

It's always possible that in reality they were always a bit less polished behind the scenes though.

It's possibly a cost benefit thing. Moving quickly with AI leaves blood splatter, but if you get enough in return you decide it's worth it anyway.

Its always more likely the company pushing the PR is less polished than they present themselves.