Twitter developers has released the Twitter Bootstrap 3 RC1 version of bootstrap. You can download this first release candidate version from getbootstrap.com. As this is a RC1 version, now there is no provision for customize and then download.
Don’t use this RC1 version of bootstrap for production. It may undergo several changes before the stable version is released. Use the Bootstrap 3 RC1 User interface framework files only for testing purpose.
For production, use only the stable version of Bootstrap. The current stable version of Bootstrap is 2.3.2. This is also available for download. You can get the stable version from getbootstrap.com/2.3.2/.
You can see the changes done for Twitter Bootstrap 3 at https://github.com/twbs/bootstrap/pull/6342.
I’ll be writing more about the new version of bootstrap in the coming days.
Read more about using Bootstrap with ASP.NET at Twitter Bootstrap with ASP.NET: List of Articles.