They are pretty high in sugar - you might find this infographic from dietdoctor.com useful. The link to the relevant section on that website is here: https://www.dietdoctor.com/low-carb/fruits
There are similar guides for other types of food too.
We call them sugar bombs in our house, great for raising your blood glucose levels when going hypo. Blueberries are the best alternative to eating them and have little impact on your blood glucose levels.
One word of caution for any fruit lovers with type 2 - fructose. Even if the glucose in the grapes doesn't raise your blood concentration by much, which it likely will, the fructose will have a small but insidious impact on your liver, and therefore insulin resistance.