Season One in Dota 2 starts 22.Nov.2017 and each season last 6 months.
Season 1 in Dota 2 will end on May 2018 we don't know the exact day because it can very few days but will update our post once we know more.
At this moment we don't know any specific rewards for a high Medal in Dota 2, the only specific rewards we know are that Medals will be displayed on your account and when the game starts from your current season.
There are seven levels of Rank Medals, and within each level are five stars of progress to earn towards the next Medal. These Medals are:
- Tier 1: Herald
- Tier 2: Guardian
- Tier 3: Crusader
- Tier 4: Archon
- Tier 5: Legend
- Tier 6: Ancient
- Tier 7: Divine
Dota 2 Season one is in the new update Dueling Fates. It will help ensure that MMR/Division is both recent and accurate for all players.