Basically all of our devices run SNMP v1 when you enable SNMP on them.

IOS devices running 12.0(3)T or higher also run SNMP v2 and SNMP v3

CatOS devices running 3.1 or higher also run SNMP v2

Just to be clear on this - if a device is running IOS 12.1(6), then it is running SNMP v1 and SNMP v2 as soon as you configure:

snmp-server community string RO

Also, the SNMP v3 engine is enabled, but you need to add numerous commands to configure SNMP v3