The Cosmos-SDK follows both 0ver and Semver. While this is confusing lets break it down: 0ver is used for the main Cosmos-SDK dependency (github.com/cosmos/cosmos-sdk) and Semver is used for all other dependencies.
Although we adhere to semantic versioning (semver), we have introduced a few modifications to accommodate the unique characteristics of blockchains. One significant divergence is that the major version (Y.x.x) is incremented solely when a consensus-breaking change occurs. On the other hand, the minor version (x.Y.x) is increased when there is a non-consensus-breaking alteration that also results in an incompatible API change. Patch versions will be bumped for all other changes that dont break the API nor Consensus.
In terms of the Cosmos-SDK dependency, we adhere to a simpler versioning approach known as 0ver. This flow differs from the previous Semver flow. Under this system, when a consensus-breaking change or an API-breaking change occurs, the Cosmos-SDK team increments the minor version (x.Y.x). Conversely, when a non-consensus-breaking change and a non-API-breaking change take place, the team bumps the patch version (x.x.Y).
