A few months back Celeste developer Matt Thorson revealed that a new chapter is headed to the game as DLC. This final update is titled Chapter 9: Farewell, and it will be free on all platforms. Farewell will be a single, continuous chapter (no B-Side) with some new mechanics, and it's said to be the hardest Celeste challenge yet.
We haven't heard much about it since January, but Matt and his team are still hard at work. The official Celeste Twitter account just broke the silence to inform fans that development is "on the home stretch." Although it won't be out this month, it shouldn't be much longer after that. The update also confirmed that the team is waiting to release the physical version of the game until after Farewell is completed.
Source: Celeste Official Twitter