Bolt 2 will require .NET 4.x and above.
Unity is making a strong move towards modern .NET scripting, and Bolt will follow suit. Indeed, starting with Unity 2018.4 LTS, the .NET 4 runtime will become default and .NET 3.x runtime will be marked as obsolete. Continuing support for a majorly outdated runtime limits our ability to provide cutting-edge features and optimal performance.
Bolt 2 will require Unity 2018.4 LTS and above and will support future Unity versions better.
We are aware that a part of our user base is still using Unity 2017.4 LTS, but a number of factor make maintaining this version impossible. Most importantly, the old Mono compiler does not support C# 7, on which Bolt is built. Unity 2018 switched to the modern Roslyn compiler, which allows us to compile Bolt from source.
Because Bolt 2 will ship as source files, we will be able to make use of conditional defines to fine-tune the plugin to the Unity version and the target build platform.
Bolt 2 will require a manual update process. A full set of step-by-step instructions will be provided when nearing beta releases. Alpha releases of Bolt 2 should not, under any circumstance, be used with existing projects; breaking changes will be introduced often along the way. We can already foresee that a script GUID migration will be necessary due to our DLL to source distribution method change.
After a successful upgrade, there will be minor breaking changes with out current design plan. Many features of Bolt 1 will also be obsoleted and replaced by better systems.