# Zyphra's ZHA makes attention search sparse with a tree structure

> Original title: Why a tree?

- Source: Zyphra
- Published: 2026-11-02T22:04:53.000Z
- Bad Influence: https://badinfluence.news/items/plojbg8g9hjb02y2hkioxsl01
- Original: https://x.com/ZyphraAI/status/2117377432797987083

## Summary

Zyphra says its ZHA method makes the attention search itself sparse, not just the final attention step. Many sparse-attention methods still pay quadratic cost in their lightweight indexers, which ZHA avoids. Unlike fixed-state models, ZHA keeps the full KV cache for precise retrieval.

## Post

Why a tree?

Many sparse-attention methods reduce final attention cost using lightweight indexers, but these still incur quadratic cost.

ZHA makes the search itself sparse. And unlike fixed-state models, it preserves the full KV cache for precise retrieval.