Guderian writes of a Russian military commission that was shown German equipment that may answer your question:

In the spring of 1941 Hitler had specifically ordered that a Russian military commission be shown over our tank schools and factories; in this order he had insisted that nothing be concealed from them. The Russian officers in question firmly refused to believe that the Panzer IV was in fact our heaviest tank. They said repeatedly that we must be hiding our newest models from them, and complained that we were not carrying out Hitler's order to show them everything. The military commission was so insistent on this point that eventually our manufacturers and Ordnance Office officials concluded: 'It seems that the Russians must already possess better and heavier tanks than we do.' It was at the end of July, 1941, that the T34 tank appeared at the front and the riddle of the new Russian model was solved.

It doesn't seem that the Germans knew much of what kinds of tanks the Russians were operating at the time, but that event may have clued them in on the fact that the Russians had quality armor, even if they had no specifics available to them.