Changelog for Patch 1.4.2.4 (added 23 August 2018):

- It's here gang! Hollow Knight's fourth free Content Pack, Godmaster, is now available for all players on PC, Mac and Linux.
- Hollow Knight: Godmaster is the final chapter of the Knight's story and the hugest content pack by far! Meet all-new characters, take on all-new quests, hunt for all-new secrets, and most of all, prepare yourself for an incredible battle to take your place once and for all amongst the gods of Hallownest!

Changelog for Patch 1.4.3.2 (added 26 September 2018):

* Voidheart' menu style now available
* Fixed an issue where game could become slower over a game session for some players
* Fixed issue where Enraged Guardian gates don't open if Crystal Guardian was defeated in Godhome
* Little weaver corpse: Audio now obeys volume controls
* Godseeker dialogue after radiance statue no longer plays in Godseeker mode
* HP reduced for Ascended/Radiant Collector's spawned enemies
* Leg Eater Discount now working correctly
* Nail arts now affected by bindings in Godhome
* Fixed issue where Dung Defender's balls got stuck in corner
* Fixed an issue where Hornet Sentinel could get stuck in wall during Godhome battle
* Fixed issue where defeating Failed Champion or Lost Kin in Godhome also counted as defeating them in Hallownest, missing achievement (if achievement was missed previously it should now be awarded when player next rests at a bench)
* Added extra check to keep Pantheon of the Master bosses out of the ground
* Fixed issue with GM's final boss where attack would telegraph in wrong position
* Improved visibility of one of that boss's attacks
* Fixed issue where completing Trial of the Fool did not unlock God Tamer's statue in Hall of Gods
* Fixed file select screen display issue
* Godmaster boss 'PV' gets stunned more frequently
* Lifeblood Cocoons in Godhome produce more Lifeseeds
* Trial of the Fool is no longer a requirement for accessing Pantheon of the Sage
* Reduced HP of Godmaster's final battle
* Reduced Markoth's HP in Godmaster battles
* Several changes to Uumuu's Godmaster incarnation
* Fixed issue where Hornet Sentinel could get stuck in corner of her Godhome arena
* Fixed issue in final battle of Godmaster where a respawn could place player in the wrong location, ruining the battle
* Fixed issue where nail arts could lose their ability to damage enemies
* Fixed issue where a mechanism could be struck while it was retracted into the ground in Godhome
* Fixed issue where players could use Dreamgate to warp out of ending sequence and bust the game
* Fixed timer display issues for main game and Godmaster pantheons
* Fixed Moss Charger's rustling grass not appearing
* In Mantis Village, disallowed enemies from approaching the Mantis Claw item to prevent possible softlock
* Game text fixes

Changelog for Patch v1.5.68.11808 (added 7 June 2021):

- Added "Borderless" option to fullscreen in video options
- 64-bit is now required (For players with 32-bit computers the previous version (1.4.3.2) can still be accessed as a beta)
- Vulkan is now the default graphics API for Linux
- Enabled controller rumble (only supported for certain configurations, e.g. Xbox One controller on Windows)
- Hopefully less hitching, and less memory usage on startup (enabled incremental GC, removed heap size increase method)
- Reduced screen tearing during screen shakes
- Fixed uncollected Grubfather rewards being miss-able
- Fixed the Soul Tyrant battle in pantheons getting stuck after being defeated sometimes
- Fixed death loop if moving too high during Absolute Radiance phase 2
- Fixed Elderbug's Greenpath hint dialogue
- Grimm chest reward is now left on the ground if you banish him without collecting it
- Fixed issues with binding mouse buttons
- Fixed multi damage sometimes taking too much health with lifeblood
- Fixed Absolute Radiance music change triggering too early if moving too high in phase 2
- Fixed Glowing Womb charm becoming inaccessible
- Sideways dash is now preferred when Dashmaster is equipped (less accidental down dashing!)
- Fixed issue where Watcher Knight's back roll was not happening
- Crystal Guardian will now wake up when damaged by area attacks (Spore Shroom, etc)
- Fixed damage inconsistency with area attacks on Radiance, Absolute Radiance, and Pure Vessel
- Fixed settings changed in pause menu being reset when quitting to menu
- Fixed damage sometimes not being applied correctly to Nail Arts when using the Fury of the Fallen charm
- Fixed dialogue box getting stuck when talking to Cloth in Queen's Gardens
- Fixed issue where closing the brightness menu in-game would in some cases restart the game
- Various minor map fixes
- Various minor translation fixes
- Other minor fixes

Changelog for patch 1.5.72.11824 (beta) (added June 25th, 2021):

Added ControllerRumbleMultiplier and CameraShakeMultiplier to Config.ini
Fixed Native Input not showing the correct state
Crystal Guardian will now wake up when damaged by Dreamshield and Grimmchild
Fixed controller screen showing Xbox 360 controller if none plugged in
Fixed Troupe Master Grimm's flame balls to now spawn from behind him
Fixed camera shake not working during hit pauses

Changelog for patch 1.5.71.11816 (beta) (skipped on GOG, as far as I can tell):

Fixed achievements for macOS (not firing in v1.5.68.11808)
Fixed nail art damage
Fixed missing effects when slashing lift spikes
Re-added native input option (on by default)
Updated InControl plugin to latest version

Changelog for patch 1.5.75.11827 (added June 28th 2021)

Fixed pantheons getting stuck at end screen when not using a controller
Fixed language setting not saving when changed within game

Offline installer: 1.4.3.2 (23987) => 1.5.75 (48176) on 30. June 2021
              [for Windows and macOS: 1.5.75 (48123) on 07. and 09. June 2021]

Changing Unity:      2017.4.10f1 => 2020.2.2f1
Size on SSD/HDD:       7.40 GB => 7.49 GB
              [for GNU/Linux installation]

# For details see the three previous changelogs ...

Update notes for Hollow Knight v1.5.78.11833
Type: Small Update / Patch Notes
Posted: Thu, October 21, 2021 @ 7:35 AM CEST

This update holds:
   o Fixed Aspid Hunters and Primal Aspids sometimes spitting immediately after breaking out of jars
   o Fixed door in a city house staying locked sometimes after defeating the enemy
   o Fixed brightness resetting on quit to menu if set to minimum value
   o Fixed some camera shakes ignoring config value
   o Fixed getting damaged by spikes while on a lift and ending up inside the ground
   o Fixed background blur for Low and Medium options when using a screen resolution that is taller than 16:9
   o Fixed Low and Medium background blur to have the same vibrancy as High

# Source: https://store.steampowered.com/news/app/367520/view/3066381328906585082

GOG Offline Installer (04.11.2021 19:00 CET):
   o Lin:   1.5.75.11827 (48176) => 1.5.78.11833 (51218)
   o Win: 1.5.75.11827 (48123) => 1.5.78.11833 (50885)
   o Mac: 1.5.75.11827 (48123) => 1.5.78.11833 (50885)
# JMB: Hollow Knight uses Unity 2020.2.2f1 on GOG since 1.5.75 ... Thumbs up for Quality of Life!

I wrote a bit more in the update thread but the current blue dot (April 9, 2023) seems to be for what is a slightly older Windows installer vs. the previous one (build went from 50885 to 50884) with most likely no changes to installed files or possibly a non-visible change to an icon. So no need to update if you have the previous 50885 build installed already. The game version is the same (1.5.75.11833) in both builds.

edit