Permission Sets: Session-Based Permission Sets Generally Available, Permission Set Metadata Behavior Change

Session-based permission sets are now generally available, and you can even use declarative tools with them. Also check out the behavior change when using metadata for permission sets. These changes apply to both Lightning Experience and Salesforce Classic.
Available in: Salesforce Classic and Lightning Experience
Available in: Contact Manager, Professional, Group, Enterprise, Performance, Unlimited, Developer, and Editions