“look at your cumulative spend and cumulative CPX metrics whether you're testing on a CPI or cost per trial or just cost per subscription and such and see when they stabilize”

Watch cumulative CPX stabilization — not a dollar threshold — to kill a test

There is no universal spend amount that signals a test is done — it depends on your CPI and funnel CPX. Instead, plot cumulative cost-per-X over time and cut when it stops fluctuating. Alper flagged accounts spending $20k to confirm what the data made obvious at $500: the signal stabilized early and was being ignored.