I know this lot are keepers because, this time around, I had the chance to come onsite (!) for the final round of negotiation and I got to meet two VPs, the chief architect, the managers of three other teams adjacent to the ones I was joining, another candidate (different role :), my upcoming manager (who had interviewed me, but this was much less formal) the lead partner engineer and the CTO.
Some of these were formal meetings but a lot of them were ad hoc 5 minute 1:1s I had while being shown around the building, being introduced to people. Everyone was open to talking about the company and I went armed with a laundry list of questions about the product to drive the conversations, mostly just letting them talk about engineering stuff.
This was all in addition to a phone screen with the longest serving engineer (an initial “sell” really, more than a screen) two rounds of interviews (pre- and post- take home test) where I also met two other managers and a future team mate. In total that’s something like a dozen meaningful interactions with employees from all parts of the tech org.
My top tips: make a point of finding out the roles of everyone you meet and insist your final on-site be scheduled around lunchtime with a tour of the office included.
The meta point being you can make the highest signal decision only once you’ve met as many potential colleagues as possible. It’s the people that make up a company culture.