Performance

uv run pytest tests/test_eventbus_performance.py -vxs   # run the performance test suite in python

Runtime	1 bus x 50k events x 1 handler	500 buses x 100 events x 1 handler	1 bus x 1 event x 50k parallel handlers	1 bus x 50k events x 50k one-off handlers	Worst case (N buses x N events x N handlers)
Python	`0.179ms/event`, `0.235kb/event`	`0.191ms/event`, `0.191kb/event`	`0.035ms/handler`, `8.164kb/handler`	`0.255ms/event`, `0.185kb/event`	`0.351ms/event`, `5.867kb/event`

Measured locally on an Apple M4 Pro with:

Runtime	1 bus x 50k events x 1 handler	500 buses x 100 events x 1 handler	1 bus x 1 event x 50k parallel handlers	1 bus x 50k events x 50k one-off handlers	Worst case (N buses x N events x N handlers)
Node	`0.015ms/event`, `0.6kb/event`	`0.058ms/event`, `0.1kb/event`	`0.021ms/handler`, `3.8kb/handler`	`0.028ms/event`, `0.6kb/event`	`0.442ms/event`, `0.9kb/event`
Bun	`0.011ms/event`, `2.5kb/event`	`0.054ms/event`, `1.0kb/event`	`0.006ms/handler`, `4.5kb/handler`	`0.019ms/event`, `2.8kb/event`	`0.441ms/event`, `3.1kb/event`
Deno	`0.018ms/event`, `1.2kb/event`	`0.063ms/event`, `0.4kb/event`	`0.024ms/handler`, `3.1kb/handler`	`0.064ms/event`, `2.6kb/event`	`0.461ms/event`, `7.9kb/event`
Browser (Chromium)	`0.030ms/event`	`0.197ms/event`	`0.022ms/handler`	`0.022ms/event`	`1.566ms/event`

Notes:

kb/event is peak RSS delta per event during active processing (most representative of OS-visible RAM in Activity Monitor / Task Manager, with EventBus.max_history_size=1)
In 1 bus x 1 event x 50k parallel handlers stats are shown per-handler for clarity, 0.02ms/handler * 50k handlers ~= 1000ms for the entire event
Browser runtime does not expose memory usage directly, in practice memory performance in-browser is comparable to Node (they both use V8)