No, unfortunately, you can't directly access any summary bar values via the API, so you would need to grab that value another way.
The typical way of doing that it is to take all of your records that you are trying to summarize and link them to one single record in ANOTHER table. Then, in that OTHER table, you can use a Rollup field to perform summary functions on all the linked records. You can grab that Rollup field via the API.
Alternatively, you can write your own custom Javascripts to perform summary functions on found records, or if you don't know how to write Javsscripts, you can use a low-code tool like Make's advanced automations for Airtable to perform summary functions on found records.
Hope this helps! If you’d like to hire an expert Airtable consultant to help you with anything Airtable-related, please feel free to contact me through my website: Airtable consultant — ScottWorld