Yes, there will be a fourth season of the TV series, 13 Reasons Why. Netflix has announced that this series will have a fourth season, and this will be the last season of the series.
The production of the fourth started around August 1 of 2019.
There is no release date yet or official trailer for the new season. Production is expected to round up in 2020 as the last two seasons took around six months to shoot.
It is safe to say that season 4 will also have 13 episodes, just like the past three seasons.
Netflix announced that season 4 would be the last season at the time the renewal of the series was announced. Netflix also announced that the core characters would be graduating from High School in the new season, so it is natural to conclude the TV show.