I have recently begun watching the BBC series World at War. Episode 5 discusses how Stalin pulled his Siberian forces away from the east when his master spy in Tokyo told him that "Japan had its eyes elsewhere." The show didn't go into any further detail, but it seemed like a foreboding notion that Stalin had some idea of what Japan wanted to do.
Am I reading too hard into this? I've heard some conspiracy theories that FDR knew about the attacks beforehand, has such a theory been espoused about Stalin? Or is there another explanation for why Stalin was so confident about pulling his Siberian forces towards the German front?
Judging by actual policy, it is unlikely that Soviet leaders were sure about Japan intentions. Possibility of invasion definetely was not outruled.
At the day of German invasion (22nd June 1941) USSR total militaty strength on the Far East (Far East and trans-Baikal military districts, Pacific Fleet, NKVD Borderguards) amounted to ~703 thousand men. As every other inner military district of Soviet Union, Far East was ordered to send its most capable divisions and regiments to repel invasion. Prior to December 1941, 10 infantry and 3 tank divisions (~67 thousand men, less then 10% of the total strength) were transferred to fight Germans and played their part in Moscow and Tikhvin succesful counteroffensives.
Far East and trans-Baikal fronts (they became fronts instead of military districts when war started) didn't sit idly after sending troops to the west. New divisions were formed and by 1st of December 1941 (days before Pearl Harbor) total strength of Far East excessed 1.4 million men and remained at comparable level until end of war. So it was not like Stalin sent all his Far East (not Siberian) troops -- only small part were transferred. Soviet Union was preparing for the worst, holding considerable force to fight potential invasion even when actual invasion was threating its very existense.