The casbah driver 3.1(.1) is compiled against the mongo java driver 3.2. (see http://mvnrepository.com/artifact/org.mongodb/casbah-commons_2.11/3.1.1).

the table in this page says casbah is compatible with mongo 3.4

the page "https://docs.mongodb.com/ecosystem/drivers/driver-compatibility-reference/#reference-compatibility-mongodb-casbah" says it's compatible with 3.2 (that would correspond to the java driver version).

So, the information is not consistent.