The problem

Windows does not properly support files and directories longer than 260 characters. This applies to Windows Explorer, cmd.exe and many other applications (including many IDEs as well as bash, perl and tcl that come with Git for Windows).

Opt-In configuration

For this reason, long paths support in Git for Windows is disabled by default.

That being said, long paths support for C-based git commands can be enabled by setting the core.longpaths option to true. Scripted git commands may still fail with this option, so use at your own risk. Example:

git config core.longpaths true

Technical background

The root cause of the technical limitation of 260 chars lies deeply within the Win32 API. Microsoft's online article Naming Files, Paths, and Namespaces describes the reasons. Git's source code itself does not have the limitation, it is Windows-only.

Implementation details

Originally introduced into Git for Windows 1.9.0, the idea to overcome the length limitation is to convert them into UNC paths (i.e. network paths of the form \\?\...). Such paths are accepted by many of the Win32 API's functions accepting UTF-16 strings (many functions in the Win32 API are available as ASCII and UTF-16 functions, marked by an A and a W suffix, respectively) and are allowed to have a length up to 32,767 wide characters. See e.g. this commit for more details.