In late August, I ate at Akershus and Teppon Edo.
We ate at Akershus for breakfast, and I felt Akershus had a LOT of options for gluten-free food. There was a good selection of meat and cheese (plus herring - eh) and lots of fruit, cottage cheese, etc. The scrambled eggs and bacon were really good. They had an amazing potato casserole dish, which unfortunately had wheat flour used as a binding agent, but I had a taste of it and it was AWESOME.
Teppon Edo was also very good. I had the steak/chicken combo and they made my food first on the grill to avoid contamination. They used La Choy soy sauce for the seasoning since it doesn't contain wheat, and my meal was lotsa veggies and the meat since the noodles were excluded. I was sort of surprised they didn't have rice noodles as an option, but the white rice was good, and you could get another bowl if you liked. The other guests got a few dipping sauces for their meat, but I didn't since all the sauces had gluten in them.