Season 4 of Overwatch Competitive Play will be ending very soon, towards the ending of May to be exact, and Season 5 will commence at the start of June, which will be one week later after Season 4 ends, as Overwatch Game Director, Jeff Kaplan posted in a thread in the Overwatch Forum. Furthermore, Kaplan also mentioned that they will be implementing a timer on the game selection menu for players' convenience to know when it will be ending. "Season 4 will come to a close towards the end of May. The Competitive Play card will update with a timer later in the month with the exact time. Season 5 should start around the first of June," Kaplan said.
Here are the rewards that you will be getting at the end of the season, which includes a Hanamura themed spray, a Hanamura themed player icon and Competitive Points for you to spend on Golden weapons. For players who are ranked in the Top 500 when the season ends, they will be awarded with a special Hanamura themed moving spray. Here is a list of how much Competitive Points you are rewarded in each rank based on Season High.
Remember that you will need to complete all ten of your placement matches on Competitive Play if you are looking to earn these rewards. If you have not completed your placement matches yet, do it now before its too late.