Although caffeine is not a carbohydrate it does stimulate the pancreas to secrete a small amount of insulin, particularly if you are prone to hyperinsulism.
If you want to, drink real Italian espresso coffee. The high pressure of steam causes the ground coffee to release its flavour in concentrated form without releasing too much caffeine at the same time. If you make your own coffee use Arabica beans, as they contain less caffeine.
Do not drink filtered coffee or instant coffee.