This is the simplified version! For technical answers, see the "expert mode" supplement.
For most cases, the answer is “snapshot 18w43b and above, releases 1.14 and above”.
There exist ways to run Fabric with older versions - modded or vanilla, but they're currently non-trivial - see the expert FAQ for more details.
A few modpacks are currently being distributed via MultiMC exports, such as All of Fabric, and some are also available on CurseForge. Don't bother with the Launchpacks - they are generally “proof of concept” and not intended for production gameplay.
As of 9th May 2020, the following launchers are available for this:
Please keep in mind that Fabric API is a separate component and must be downloaded separately - you can find it here.
We recommend MultiMC due to its superior user experience for modded environments.
As of 30th June 2019, the following launchers are available for this:
Please note that we have no information or ETA regarding support by the Twitch Launcher.
Not at the moment. This may change by the end of the year, but is unlikely to be officially supported.
The development team does not consider Forge interop a high-priority goal, as our focus in our limited time dedicated to the project is on supporting the Fabric community and its developers and users.
Not officially. However, unofficial mods exist to faciliate the launching of OptiFine for 1.14+ on Fabric. Your mileage may vary, however.
Fabric's rendering patches, while as minimally invasive as possible, make some assumptions about the data format used internally by the vanilla rendering system. Shaders break this assumption, so things go awry. Workarounds do exist and are implemented by the most recent versions of said unofficial mods.
DO NOT downgrade Fabric API as a workaround for this. It's a bad idea.
Not at the moment. Sponge does not yet have a ready API or a working implementation for 1.14, the Minecraft version that Fabric runs on.