With immediate effect following today's update, the Ranked Medals of all players will be reset and each player will have to go through ten ranked calibration games to regain a new Ranked Medal.
As announced by Valve in the November 2017 update which reformed ranked matchmaking and introduced a new system of Ranked Medals, the first six-month ranked season has now come to an end. Today's update will signal the start of the second Ranked Season, hence resetting the previous medals of all players and giving fans a shot at redemption by re-calibrating their medal in a series of ten ranked calibration games to a new medal. As promised by Valve, this "will allow for a substantial change in rank based on your performance during calibration, seeded by your previous rank"
In other news, the Ranked Matchmaking system itself has also undergone a few adjustments. As signaled by fans all over the world, a much welcome change is signified by the ability of a player to now track his progress to the next star of his ranked medal. Additionally, the stars of Ranked Medals will now be numbered from one to five, whereas previously the stars for each respective Medal were from zero to five. The update also includes glad tidings for Dota veterans, for whom the exclusive rank of 'Immortal' will be reserved which will feature their ranking on the leaderboard instead of stars.
As always, there is always much speculation about the calibration system and how new ranks will be calculated. In the past, there have been many gimmicks with players spamming Oracle's Purifying Flames for high hero healing and Zeus' Thundergod's Wrath for high hero damage in attempts to maximize their rank. However, the Valve employee in charge of the programming for the new re-calibration system has himself been generous enough to let players know (via a Reddit comment) what factors will be taken into account for rank calibration in the new system, dismissing all rumors which say otherwise.
source: Dota 2 official blog
