PHP 8.0 is now required, given the addition of expanded and stricter typehinting.
Statement-building proper has been extracted to the Atlas.Statement package.
The 1.x method Query::getStatement() has been renamed to
Statement::getQueryString().
The 1.x method Query::getBindValues() has been renamed to
Statement::getBindValueArrays().
When using a subselect as an inline value, you no longer need to call
getStatement() or getQueryString(). Indeed, you must not, if you want the
bound values to transferred to the receiving query properly.
Generated placeholder tokens now have a different format; whereas in 1.x they
were composed of a single number (:__1__), they are now composed of two
numbers (:_1_1_). The first number corresponds to the number of query
instances; the second is the count of bound values on that query instance.
If you depend on the placeholder token format, e.g. in your tests, you will
need to update your expectations.