No dress code as far as I'm aware, but most people are in business casual. Reservations aren't required. I'd recommend getting one for busier nights because even though the place is huge it does fill up.
I went there without a reservation and just wore casual attire. Had no issues.
I went for lunch and reservations were not required but made them anyway. Dress code for lunch was casual but neat.
They take reservations, and can fill up on a busy night, but you can sometimes find open high tops by the bar area. I don't think there is a dress code, but it is a dressier type place so you may feel out of sorts if you come dressed very casually.
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