Given an @Entity with @GenerationType.AUTO:

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
public Integer getId() {
    return id;
}

Hibernate 4.x generated the following SQL:

create table MyEntity (
    id integer generated by default as identity (start with 1),
    primary key (id)
)

Now, with Hibernate 5.x, this behaviour changend to:

create sequence hibernate_sequence start with 1 increment by 1
create table MyEntity (
    id integer not null,
    primary key (id)
)

This breaks my testcases, since the sequence hibernate_sequence is also being used by all other entities, so I can't rely on certain entities having certain IDs.
One might argue that relying on IDs is a bad practice, admittedly.
But the point is that the default behaviour just changed.
I've checked the JPA Spec for further details about @GenerationType.AUTO, but I didn't find any.