Joking aside, one of the places I worked tried to hire an ex-Google CTO, He basically wanted to be the CTO and then have 20-30 developers reporting directly to him. That to me is flat. And that did not fly well with the business people. "No! We must have 3-4 subordinates max under each role, reporting up the hierarchy!" I imagine you can't grow to a large size without hierarchy, but with 20-30 people it is possible to be flat.