The correct answer is A. Artifact ID. Relativity's official Production Sets documentation states that in the Sorting section of a production, if no custom sort criteria are selected, the default sort order is Artifact ID , which Relativity describes as the load order of the documents. This is the platform's documented default for productions.
This is an important administrative detail because production sort order affects how documents are sequenced when a production is generated. Relativity also notes that when you apply a custom sort order, family groups are not kept together automatically , so administrators need to design sort strategies carefully if they want a specific production sequence. But absent any special configuration, Relativity defaults to Artifact ID.
The other options are not the documented default. Family group may be relevant in review workflows, but not as the production default sort order. Control number is also not the starting sort value because control numbers may be assigned independently of the production sort configuration. Custodian is a common field for review and QC, but again not the production default. Therefore, the correct answer is A. Artifact ID .