Google posted Android 4.3.1 ( codenamed JLS36I ) factory image for latest Nexus 7 LTE variant. You can grab it from Google Developers website and make sure check-sum of the downloaded file matches with posted value.
It looks Android 4.3.1 update is just limited to Nexus 7 LTE and the change log is tiny.
Some Security patches & Bug fixes
Google Keep pre-installed