You can now set the model units you want to use when exporting a model into STEP format.
To do this, you will go to System Options>Interoperability>STEP
You will select the desired unit of measure from the dropdown and click OK.
If you have the Show popup on export checkbox checked, you will see a message show up each time you export notifying you of what units the file was exported in. This is handy to have turned on if you regularly switch between metric and imperial units.