I wrote a connector for Sybase back in 2000, based on our existing one for MS SQL Server 7, and some things had already changed on the protocol level.

I don't remember exactly what and why, just that for some specific DML commands another kind of connection was required.

The split must have happened in the mid nineties (I think) with SQL Server 6 and Sybase 10. The next version after 4.9.

It's notable that 10 was the worst Sybase version, ever.

Source: I worked for Sybase Professional Services from 95 - 99.