With a standard S3 configuration: AWS_ACCESS_KEY_ID: [AWS ID] AWS_BUCKET: [bucket name] AWS_REGION: [region] AWS_SECRET_ACCESS_KEY: [secret] I can upload a file to S3 (using direct upload) with this Rails 5.2 code (only relevant code shown): form.file_field :my_asset, direct_upload: true This will effectively put my asset in the root of my S3 bucket, upon submitting the form. How can I specify a prefix (e.g. "development/", so that I can mimic a folder on S3)? Sorry, that’s not currently possible. I’d suggest creating a bucket for Active Storage to use exclusively. My current workaround (at