As of Wednesday October 4th, 2017, your campaigns in AdWords can spend up to twice the average daily budget that you have allotted.
The announcement was first spotted right in the AdWords interface and an official tweet from @adwords went out just after 3 PM.
A notice has also been appended to the AdWords support doc at https://support.google.com/adwords/answer/1704443 which reads:
Prior to this update, campaigns could spend 20% more than the daily budget but overall spend would not exceed your monthly charging limit.
So, now its uncapped but under the same constraints.
We get the concept, how it will play out remains to be seen.
Essentially, Google wants to account for the peaks and valleys in campaign performance day-over-day.
Some days your campaigns could perform better and therefore should have the opportunity to spend more than the daily budget to keep garnering quality performance stats like clicks.
Counter to that, slower days are used to basically “balance the equation.”
Our team will be keeping a close eye on the affects this major change may bring about.
It is expected that while daily spends may experience some intense fluctuations, the outcome will still be that accounts don't exceed the monthly calculated budget.
Instead, accounts should simply see their monthly spend edge just a tad bit closer to their max cap.
Do note that there's no need panic and start lowering or increasing budgets. Until more data can be analyzed it is best to keep things status quo.