On January 7, 2020, Microsoft released SQL Server 2019 Cumulative Update 1, which is Build 15.0.4003.23. By my count, there are 66 public hotfixes in this cumulative update, which is a larger than average number.
I think this can be explained by the fact that it is the first cumulative update for SQL Server 2019, and the fact that it has been slightly over two months since SQL Server 2019 went GA (so it is a little late).
If Microsoft follows the same procedure as they did in SQL Server 2017, they will be releasing a new CU every month for the first twelve months after GA. After the first year, they will then release a new CU every two months for the next four years. After five years, SQL Server 2019 will fall out of Mainstream support, so there won’t be any more cumulative updates after that.