You will start by being the smartest person in the room. That will quickly change. Some of those smarter people who arrive on the scene will make their superior intellect known. It takes a lot of self confidence, combined with humility, to lead really smart people. This is true across disciplines. You'll more frequently be in a room with smart people who feel the need to speak up. More often than not, their input will be more valuable than yours, so let them speak. Every once in a while, however, you will need to speak up to correct some less-than-accurate thinking about some thing or another. Historical context may be required, principles you've built the organization on might be violated, they might just be wrong. There will also be a lot of people who's perception of their own intellectual value to the organization is over-sized. When their own perceived value to the organization is too far out of sync with their actual value to the organization, that's when there is almost always a problem.
You will go from knowing about every change to the product to not very many. People will ask you when a particular change went out and you won't know the answer. (This might be particularly true if you practice continuous deployment, which you should.) You'll need some process to manage all these things you don't know about.
There's so much reading involved. Not just books and blog posts. Specs. Documentation. RFCs. Meeting notes. You'll feel always behind the eight ball just like you do with your read later queue.
Being an effective writer will become increasingly important, but take just as long as ever.
The ability to keep a meeting moving is invaluable.