10.5-inch iPad Pro Screenshots and App Previews Now Supported.

You can now upload 10.5-inch iPad Pro screenshots and app previews by visiting Media Manager in iTunes Connect. If you choose not to provide these additional assets, your 12.9-inch iPad Pro screenshots and app previews will display on both device sizes.

Screenshots
1668 by 2224 pixels (portrait)
2224 by 1668 pixels (landscape)

App Previews
1200 by 1600 pixels (portrait)
1600 by 1200 pixels (landscape)
4:3 aspect ratio

Learn more about uploading screenshots for specific device sizes and languages in iTunes Connect Developer Help.