There is no option to save a file as an Excel 2007-2013 XML Template (.xltx). I expect this would be simple functionality to add to improve compatibility.
Name: [Content_Types].xml <?xml version="1.0" encoding="UTF-8" standalone="true"?> -<Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types"> Test.xlsx\ <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml" PartName="/xl/workbook.xml"/> Test.xlts\ <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.template.main+xml" PartName="/xl/workbook.xml"/> Test.xlsm\ <Override ContentType="application/vnd.ms-excel.sheet.macroEnabled.main+xml" PartName="/xl/workbook.xml"/> Test.xltm\ <Override ContentType="application/vnd.ms-excel.template.macroEnabled.main+xml" PartName="/xl/workbook.xml"/>
Apparently this has already been reported, setting as duplicate. *** This bug has been marked as a duplicate of bug 99438 ***