Hollow Knight is without a single doubt one of the best games from 2017, a fact that I'm reminded of every couple of months as the developers just can't stop releasing major updates for it. While the previous ones were more like mini-expansions, the upcoming Lifeblood Update is more centered around improving and polishing what is already present.
As such, you can expect to see numerous balance tweaks, improved performance across a variety of machines, a whole host of bug fixes, additional sound effects and voices, and for those among you that don't like having to memorize every major location on the map, the ability to purchase map markers! There will also be a brand new boss fight with its own unique music track, a significant rework of one of the original bosses, as well as a bunch currently unannounced extras to peruse.
The Lifeblood Update is set to arrive in about a week, but if you would like to potentially speed it up and get a bit of a sneak peek at the same time, you should join the public beta on Steam. You'll find the download instructions, as well as a list of known issues, over at the Steam forums.
Before you dive in, however, make sure to back up your save files! I haven't encountered any problems with my saves, but it's still better to be safe than sorry, especially when a 100% playthrough can take upwards of 60 hours at a leisurely pace!
You can learn a little bit more about the Lifeblood Update, as well as the slowly approaching Switch release, by heading over to the official website.