Business casual is implied. I don't believe they wouldn't seat you if not dressed up but you may feel out of place.
To fit in you need to be dressed well enough to feel comfortable at an expense restaurant in Kirkland
Technically no, but everyone that you'll see there is dressed to the nines. It's more an implied dress code. My mother and I went there for my birthday, dressed in high-end hiking clothes. We weren't exactly casual looking, but at the same time we were put in an area that wasn't visible to others. This was fotunate since we then had a private dining experience, but I wouldn't count on this happening again. As I side note I HIGHLY reccomend this restaurant, it is extremely good!
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