MySQL Partitioning a table with an auto incrementing BIGINT unique primary key

MySQL Partitioning a table with an auto incrementing BIGINT unique primary
key

I have a hypothetical table with a primary key that is a BIGINT. Let's say
my table grows very large and I have to partition and create different
partitions by date range. What happens with primary key? Does that mean I
can exceed the capacity of the BIGINT since there are more tables now? How
does MySQL keep from assigning duplicate primary keys assuming a BIGINT
set to auto increment a unique value?
Thanks in advance...