CBP now gathers travelers arrival/departure information automatically from their electronic travel records. CBP estimates that the automated process will save the agency $15.5 million a year. Beginning in May 2019, I-94 numbers will be alphanumeric, following the format of 9 digits, followed by a letter in the 10th position, and a digit in the 11th position. The current numeric-only format will continue to be valid in the Ad-I-94 date displayed on the date of the date.”]
Source: https://www.cbp.gov/travel/international-visitors/i-94