I found https://github.com/beeminder/beedroid-api but given that last activity is in 2014 I am not sure whatever I should bother with it.
I know that Android Beeminder app is unlikely to be open sourced in the near future, so I am considering writing my own client.
Also, it seems that way how I use beeminder is quite diverged from needs of a typical user. For example I want an easy ability to set break in the future, and I want to eradicate graph images as for me all of them seem to not be useful (despite that I love graphs for almost everything).