Found under your Twitch dashboard → Settings → Stream → Stream Key. This is the same key OBS uses — no OAuth needed to go live.

Changing this rescales every existing layer in every scene to fit, so nothing shifts out of frame.

A cap, not a guarantee — your connection can still push it lower under real congestion, but this stops the encoder from chasing a higher number than it should and tells it to hold resolution steady and drop framerate first if it has to give something up. 4500–6000 kbps is typical for 1080p30 on Twitch; go lower if your upload can't sustain that. Applies immediately if you're already live.