In 2017 a nation-state actor used massive firepower that amounted to more than 2.54 terabits per second. The actor targeted thousands of Google IP addresses at the same time and used several attack methods in a campaign that span across multiple months. Google did not attribute the attack to a particular actor but said that the bad UDP packets hurled at its systems came from devices using several Chinese internet service providers. Google warns that while its report shows the scale of past and current DDoS attacks and can help predict the size of future ones, defenses must be over-provisioned.
Source: https://www.bleepingcomputer.com/news/security/nation-state-actor-hit-google-with-the-largest-ddos-attack/