Researchers have successfully made zip-zip trees "partially persistent," allowing them to preserve previous versions of the data structure with minimal space overhead.
Like their predecessors, they are history-independent , meaning the tree's final structure depends only on the keys it contains, not the order in which they were inserted or deleted. Current Developments (2025–2026) Updated Zipzip
solve this by introducing a double-ranking system: Balancing the Bias: By using two independent ranks ( they are history-independent
), zip-zip trees ensure the expected depth of the smallest key is identical to the largest, resulting in a more uniform and balanced tree. Updated Zipzip
New "just-in-time" models have been developed that use an expected constant number of bits (