What is Field Audit Trail and how does it differ from standard Field History Tracking?

Standard Field History Tracking retains up to 18 months of field change history (who changed what, when, and the old/new value) in the FieldHistory related list. It is limited to 20 fields per object. Field Audit Trail (a Shield feature) extends retention up to 10 years and supports up to 60 fields per object. It stores data in a separate BigObjects infrastructure (FieldHistoryArchive), enabling long-term compliance with regulations like GDPR or HIPAA audit requirements. Field Audit Trail also captures changes from API integrations and automated processes. Data can be queried via SOQL against the FieldHistoryArchive object but with certain restrictions on filtering.