The modified_at field value will be the date of the last modification to the data object in Merge's database. Note that this will be different than the date an object may have been updated in the third-party system. This field value can be leveraged for filters to query data modified before or after a specific date.
For example, if you would like to query data that was modified after 01/01/2022, you can use the modified_after timestamp filter. This will query data that has a value within the modified_at field after the date of 01/01/2022. You can also use the modified_before timestamp filter to do the opposite and pull data before.
More information on timestamp filters, which leverage the modified_at field, can be found here.
How does it get updated?
The modified_at field will be updated when there are changes to non-remote_data fields. This includes all data that is part of the standard common model fields for a specific object but does not include additional fields that are found in remote_data.
Recommendation when accessing remote_data:
If you are trying to access fields within remote_data, it is recommended not to use a modified_before or modified_after filter. Since changes to remote_data will not change the modified_at field value, these timestamp filters will not fetch the requested data if they were updated.