I decided to eat at the Soiree Room at Upstairs on the Square after seeing it listed on this website (and checking the restaurant's website to confirm that there is a vegan tasting menu). However, when I got to the restaurant, the waitress only gave us the option between two tasting menus, neither of which were vegan. Fortunately, after I mentioned to her that I came explicitly for the vegan tasting menu, she talked to the chef and said that he would be able to prepare a similar vegan tasting menu for our party.
(Note: In order to avoid being in a similar situation, I would recommend explicitly mentioning if you're vegan when making your reservation - while they were happy to accommodate us, I think they would have preferred to have a little more time to plan for our meal)
In spite of the impromptu nature, we were still treated to a panoply of exotic dishes and wine pairings. The chef was even careful to adhere to our vegan diets while still treating us to all of the perks enjoyed by the other restaurant patrons. He sent olive oil and balsamic vinegar to go with our bread (instead of butter), grated white truffles over our salad (instead of grating cheese) and the maitre d' arranged for all of our wine pairings to be biodynamic/organic.
Our favorite dishes were the amuse bouche (a tempura green bean in a spicy/sweet wasabi/fruit sauce over a slice of avocado), the watermelon gazpacho (with sweet tarragon and yellow watermelon "foam"), and the dessert: strawberry sorbet over a bed of blueberries, coated in a red wine reduction.
The only "downside" is that the entire meal (including wine) ended up being about $150 per person, but I thought it was a worthwhile price to pay for a truly special evening.