Campaign Budget Optimization

With Campaign Budget Optimization, the advertiser sets one total budget on the campaign, and Meta's delivery system shifts spend between ad sets in real time toward whichever is producing the cheapest results, based on the campaign's optimization event. This removes manual budget-shifting but also means a promising new ad set can get starved of spend before it exits the learning phase if an older ad set is already winning.

Agencies running many ad sets for creative testing often prefer ad set budgets (ABO) during the test phase specifically to guarantee each variant gets a fair amount of spend, then switch winning combinations into a CBO campaign once creative and audience are validated, to let the algorithm allocate at scale.