This is a bugfix release with no breaking changes. 3.9 users are advised to upgrade if possible.

Contributors to this release: antonhornquist, aspiers, brianlheim, cappelnord, florian-grond, gusano, jamshark70, patrickdupuis, redFrik, shimpe, telephon

• supernova only looked for plugins in a plugins/ subfolder of the provided extensions directory. This has been fixed to be consistent with scsynth (#3433).
• Fixed Index, IndexL, FoldIndex, WrapIndex, IndexInBetween, and DetectIndex incorrectly downsampling audio-rate index arguments (#3436).
• The GUI class library folders were installed even when building sclang without Qt, resulting in unbound primitives. This has been fixed (#3456).
• Some default class library directories had to be manually created. sclang will now create them for you if they don’t exist (#3469).
• Fixed a Routine not being properly terminated when running CmdPeriod.run (or hitting an equivalent shortcut) when a Server:plotTree window is open (#3423).
• Fixed LevelIndicator:style_ doing nothing and printing the warning Qt: WARNING: Do not know how to use an instance of class 'Meta_QLevelIndicatorStyle' (#3398).
• Fixed Git.checkForGit returning nil (#3445).
• The SynthDef compiler optimizes a + b.neg to a - b, but other UGens that depend on b.neg would also be incorrectly removed in some cases. This has been fixed (#3437).
• In 3.9.0, the group key broke in the “grain” event type. This has been fixed (#3483).
• New IDE themes have been introduced for the editor and post window: Solarized, Solarized Dark, and Dracula (#3412, #3410).
• Set the default font in the IDE for macOS to Monaco, instead of the rather silly non-monospace font that has been the SC default for over a decade (#3404).
• Fixed duplicate SCIDE icons in GNOME, and fixed the SCIDE icon looking wrong (#3380).
• Fixed SCDoc breaking with page titles containing a single quote character (#3301).
• Fixed an error due to lack of input sanitization when trying to open help (Cmd+D/Ctrl+D) or references (Cmd+U/Ctrl+U) on text containing a double quote character (#3277).

You can download SuperCollider 3.9.1 from the release page.