Normal sudoku rules. Digits in cages must sum to the small clue in the top left corner of the cage. Within cages, digits may not repeat.
Additionally, cages without a sum are “hesitant” and must join one of the adjacent "normal" cages (cages which do have a sum) to form a combined larger cage with the same sum as before. Hesitant cages may also join other adjacent hesitant cages as long as they eventually join a normal cage.
(For example the 24 cage which starts in C3 must be one of these arrangements in the finished puzzle)
The puzzle is also available on f-puzzles
Solution code: Boxes 2 and 8, each box from top left to bottom right