Not sure what you mean, Spotify tracks have long exposed "features" that include various metrics to judge mood. https://developer.spotify.com/documentation/web-api/referenc...

Also it's pretty apparent since Spotify suggests different playlists depending on time of day, weather, etc.

Do they only judge a song's mood, or do they judge the listener's mood and store that alongside the location?

Each song gets analysed and assigned ~10 audio parametres. If you tend to like tracks with, say, high danceability in the past X days, you're gonna get recommended more tracks with high danceability.

If you listen to a specific genre, it's gonna work great. If you tend to listen to unrelated tracks, your recommendations are gonna be shit. If you listen to a couple of albums that are really not what you listen to usually, it's gonna take you a while to get rid of similar tracks from your recommendations.

So to answer your question, it's more of a snapshot of the mood of the tracks you've interacted with recently, not your mood specifically.

I guess I didn't realise that they kept full IPs for such a wide range of time - I was kind of hoping they were anonymizing them after some time...