The APPLY INTO function for SCD2 historization typically sets the __END_AT field of current records to NULL rather than a "highgate" like 9999-12-31. This is by design and reflects that the record is still current and has no defined end date yet.

Currently, there is no built-in option in APPLY INTO to set a highgate value such as 9999-12-31 in place of NULL for the __END_AT field. The common and recommended practice in querying such SCD2 tables is to use COALESCE on __END_AT during point-in-time queries, for example:

This approach avoids assuming a default date on data insertion and clearly specifies that NULL __END_AT means "open-ended" or current record.

In summary:

• APPLY INTO currently sets __END_AT to NULL for current records (no explicit "highgate").

• There is no native setting to replace NULL with a highgate date in APPLY INTO.

• Using COALESCE in your queries is the standard way to handle the NULL __END_AT in point-in-time filtering.

This design aligns with Delta Live Tables and Databricks implementations where NULL __END_AT signifies an active record's open-ended coverage, and your query patterns accommodate that appropriately.​