Afer reviewing the new Blockchain Defensive Patent License - BPDL, we think it would be beneficial for the community to have a central place for the stratum protocol specification. At the same time, the proposal for stratum protocol extensions has been approved and marked as BIP310.
Basic Stratum specification
For the time being, the basic/original Stratum Specification is still available through the Slush Pool website. The plan is to migrate this information to this site.
Slush Pool Team