title: Xcode Project Format: what are the differences between 3.1, 3.2, 6.3 and 8.0?
body: <p>When I open a project in <strong>Xcode 9</strong> (or previous versions) and check the File Inspector, there's a section called Project Document, with a combo box named <strong>Project Format</strong>.<br>
  The available options (in <strong>Xcode 9</strong>) are <code>Xcode 3.1-compatible</code>, <code>Xcode 3.2-compatible</code>, <code>Xcode 6.3-compatible</code>, and <code>Xcode 8.0-compatible</code>: </p>
  
  <p><img src="https://i.stack.imgur.com/4jesr.png" alt="Project Format Options"></p>
  
  <p>What are the differences between those formats?</p>
  
  <p><strong>-- UPDATE HISTORY (as of 20 May 2019) --</strong></p>
  
  <p>I originally asked this question when <strong>Xcode 6.4</strong> was around.<br>
  <strong>Xcode 6.4</strong>'s list included <code>Xcode 3.1-compatible</code>, <code>Xcode 3.2-compatible</code> and <code>Xcode 6.3-compatible</code>, and defaulted to <code>Xcode 3.2-compatible</code>.<br>
  <strong>Xcode 7</strong> didn't introduce any changes.<br>
  <strong>Xcode 8</strong> added an <code>Xcode 8.0-compatible</code> item.<br>
  <strong>Xcode 9</strong> changed the default for new projects to <code>Xcode 8.0-compatible</code>. (8 Oct 2017)<br>
  <strong>Xcode 10.2</strong> added <code>Xcode 9.3-compatible</code>, <code>Xcode 10.0-compatible</code> (May 2019)</p>