Comment 9 for bug 1717040

Regarding format version :

- All versions < v1.0 are considered experimental. This used to be clearly labelled on the project's homepage, though it has been updated since then. zstd is only branded and supported by Facebook since v1.0.
- Technically, the compression format has been settled at v0.8.0, so all versions >= v0.8 are compatible with each other.
- zstd contains an optional backward compatibility module, which is enabled by default in both CLI and library. This module makes it possible for newer versions to read older versions, but *not the other way round*. Therefore, v1.0+ will be able to read data produced by v0.5.1, but v0.5.1 will not be able to read data from v1.0+.
- Note that the compatibility module is optional, and a number of projects have selected to not include it. Such projects are therefore unable to read data produced with v0.5.1. This includes, for example, the Linux Kernel codec (integrated in 4.14).

Hope it helps