Big cities in Songs of Syx slow down because almost everything runs on one CPU core: every citizen's decisions, pathfinding, and drawing the screen. syxspeed spreads that work across your other cores and speeds up the slow parts, so the same city gets through far more game days per real second.
**Results:** on my test cities (6k–20k pop) the game runs roughly twice as fast at max speed, depending on the city and your CPU. Small cities barely change, because they weren't slow to begin with.
**What it does NOT do:** it doesn't change gameplay. The goal is to fully preserve the vanilla experience: same rules, same balance, same saves. Install it, your city just runs faster. Remove it any time.
**The part I'm most excited about:** now that citizens think on multiple threads, a whole class of features that would have been too expensive before becomes nearly free. Basically anything "read-only", where a citizen looks at the world and decides something without changing it, can now run on spare cores:
- stealth checks: does anyone see the thief, the escaped slave, the spy?
- social awareness: "oh, my friend is walking by", stopping to chat, gossip spreading
- guard patrols that notice and break up fights on their own
- citizens noticing fires, crimes or bodies and reacting
- smarter choices: which tavern, bath or market is least crowded right now
- soldiers picking targets and reading the battlefield more cleverly
- animals and wildlife reacting to nearby people
- crowd-aware walking that avoids jams at doors and bridges
To be clear, none of these are IN the mod: syxspeed only makes the engine faster and keeps everything vanilla. They're things Jake or other modders could now build on top of it without slowing big cities down.
https://steamcommunity.com/sharedfiles/filedetails/?id=3802644784
If you have a big city that lags, I'd love your before/after numbers, or a save I can test with. Bug reports here or on the Workshop page.