Two approaches are possible, depending on what your goal is.
Display Purposes Only, Don't Want Extra Field
This isn't a function in ModelBuilder, but rather a question of how the number is being displayed in the attribute table. Here's how to change that (based on these instructions):
- Right-click on the field heading (SUM_Acres_) and choose "Properties"
- Click the
... button next to "Numeric"
- In the next window, check the "Show thousands separators" box.
(You can also reduce the number of decimal places it shows in the same dialog.)
The Data Needs That Comma, An Additional Field Is Fine
If you want this to be all contained within one ModelBuilder operation and/or done automatically for you, the table will need to have a new field. (This can simplify subsequent sharing, labeling, etc. since the previous method will only affect the attribute column display, not the underlying data.)
Two additional operations are required in the model for this:
Add Field: Add a new field. Make sure that the new field type is
Calculate Field: Use the expression
format(int(!SUM_Acres_!), ",") in the field calculator: this will both remove trailing decimals, and include commas as thousands separators.
ModelBuilder can be quirky about the fields it lists after an Add Field operation, so you might need to type in the name of the new field. Make sure that Expression Type is set to PYTHON not VB.