What is FIO Version 2.0?
After the original FIO release, the FIO development team encountered a core design issue that, if not corrected, would have forced updates to the FIO core chain code for every feature release.
The design issue is related to how FIO whitelists public contract actions as part of chain security. FIO’s initial design had this whitelist hardcoded in chain code instead of being maintained in state. Version 2.0.x is a required update that introduces FIP-12 (https://github.com/fioprotocol/fips/blob/master/fip-0012.md) which moves the whitelisted actions table into state.
This will significantly simplify and accelerate the release of new features in the future. Because this is a required update, FIO nodes that have not upgraded by September 16 will be forked off of the primary chain.
Read more in the FIO Medium post.