if we have a sport_id column which is int4 and the table has a lot of existing sport_id values but contains no nulls, are these two statements the same?

alter table customer alter sport_id type int8;

ALTER TABLE customer ALTER COLUMN sport_id TYPE int8 USING sport_id::int8;

The docs imply that there will be an auto-conversion, so we are assuming that the results will be the same, but is there any subtle differences?