Google just announced yesterday that over 100,000 ads.txt files have been published, 750 of the comScore 2,000 have ads.txt files and over 50% of inventory seen by DBM comes from domains with ads.txt files.
Since 8th November, DoubleClick Bid Manager and AdWords are not buying ads from ad networks / exchanges not declared on Ads.txt. Google also says that “DoubleClick Ad Exchange and AdSense publishers that use ads.txt are protected against unauthorized inventory being sold in Google auctions.” To do this, Google “crawls daily over 30m domains for ads.txt files.”
Here a graph that shows the Ads.txt adoption:
Listen here the podcast episode about Ads.txt