I suppose you'll just have to wait for Mueller to wrap up his probe into the matter.
Several GRU officers have been brought up on charges related to the hacking of the DCCC and DNC, the subsequent dissemination of their findings to Wikileaks, and related payoffs. This suggests that there is concrete evidence that the GRU was collaborating with Wikileaks, it's just not yet publicly available.
The investigation has taken very little time as yet relative to other investigations of sitting presidents (chart is ~4 months old, but we still have only possibly reached the end of the next shortest investigation) [0]
Several GRU officers have been brought up on charges related to the hacking of the DCCC and DNC, the subsequent dissemination of their findings to Wikileaks, and related payoffs. This suggests that there is concrete evidence that the GRU was collaborating with Wikileaks, it's just not yet publicly available.