Format Versioning and Stability
Starting with version 1.0.0 (not yet released), Apache Arrow utilizes two versions to describe each release of the project. These are the Format Version and the Library Version. Each Library Version has a corresponding Format Version, and multiple versions of the library may have the same format version. For example, library versions 2.0.0 and 3.0.0 may both track format version 1.0.0.
For library versions prior to 1.0.0, major releases may contain API changes. From 1.0.0 onward, we follow Semantic Versioning with regards to communicating API changes. We expect most releases to be major library releases.
A newer versioned client library will be able to read any data and metadata produced by an older client library.
So long as the major format version is not changed, a newer library is backward compatible with an older library.
An older client library must be able to either read data generated from a new client library or detect that it cannot properly read the data.
An increase in the minor version of the format version, such as 1.0.0 to 1.1.0, indicates that 1.1.0 contains new features not available in 1.0.0. So long as these features are not used (such as a new logical data type), forward compatibility is preserved.
A change in the format major version (e.g. from 1.0.0 to 2.0.0) indicates a disruption to these compatibility guarantees in some way. We do not expect this to be a frequent occurrence starting with the 1.0.0 library and format release. This would be an exceptional event and, should this come to pass, we would exercise caution in ensuring that production applications are not harmed.
We have made no forward or backward compatibility guarantees for versions prior to 1.0.0. However, we are making every effort to ensure that new clients can read serialized data produced by library version 0.8.0 and onward.