Xcode 4.0.1 Release was released on 23 Mar 2011 and requires macOS 10.6.8+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/xcode_4.0.1_and_ios_sdk_4.3/xcode_4.0.1_and_ios_sdk_4.3.dmg.
Release notes are located at https://download.developer.apple.com/Developer_Tools/xcode_4.0.1_and_ios_sdk_4.3/xcode_4.0.1_readme.pdf.