See the footnote in the Frames and Blocks in Beamer section of the Org mode manual:
(1) If ‘BEAMER_ENV’ is set, Org export adds ‘B_environment’ tag to
make it visible. The tag serves as a visual aid and has no semantic
The default LaTeX class can be set with
at the top of the file, so you can have them commented out:
# #+LATEX_CLASS: article
and select which one you want by uncommenting one or the other. This should be enough for manual export: when you automate the process, you will probably want to use a different method,...
(If I understand well,) the correct way to do this is to replace #+BEAMER_FRAME_LEVEL: 2 by H:2 in the global options:
#+TITLE: Abandon all hope
* First page
** second stuff
* Second page
See for example here: ...