If you were like me, you had hard time finding how long exactly is the new CentOS Stream going to be supported. Carl George from the CentOS Project gave me the following answer.
CentOS should be supported roughly 5-6 years.
CentOS Stream 8 is supported from 2019-09-24 to 2024-05-31 which is 4 years and 8 months.
Next releases such as CentOS Stream 9 should reach almost 6 years of support.
Here is his Twitter answer.