Is the open class final or non-final?

Non-final. The keyword open explicitly indicates that you can inherit from this class and override its members.

open class BaseClass {
    open func someMethod() {
        // Default implementation
    }
}

class DerivedClass: BaseClass {
    override open func someMethod() {
        // Overridden implementation
    }
}

Let's compare with other access modifiers:

Modifier	Inheritance	Overriding members
private	No (within file/scope)	No
fileprivate	No (within file)	No
internal	Yes (within module)	Yes (within module)
public	Yes (within module)	Yes (within module)
open	Yes (in any module)	Yes (in any module)
final	No	No

A class or member marked final cannot be overridden or inherited, making it final. open does the opposite.