multi threading mode enabled by default
It's been some time when we released MT support, and HA+MT. We tested this extensively and code looks stable. Also according to performance tests results, Kea running in MT mode with poorly optimised configuration (incorrect thread count and queue size for different backends) is much faster than ST mode.
Making this step before releasing next stable is reasonable thing to do.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information