Sony's flagship APS-C with IBIS, large battery, and the most features in the A6000 line.
The Sony A6600 launched in 2019 as the flagship of the A6000-series APS-C line. By adding 5-axis IBIS, the large NP-FZ100 battery, and Real-time Eye AF to the A6400's foundation, it created the most fully-featured Sony APS-C body until the A6700 arrived.
Key features include the 24.2MP sensor, 5-axis IBIS, Real-time Eye AF and Tracking, 11fps burst, 4K video without recording limit, weather sealed body, and the NP-FZ100 battery providing approximately 810 shots. The body has a larger grip than the A6400.
Sony E mount. The A6600 sits above the A6400 with IBIS and better battery, below the A6700 with AI AF. The A6700 with its newer processor and AI subject detection is the current recommendation for new purchases.
Good value used as the A6700 has superseded it. Check IBIS operation, battery health, and AF tracking performance. The IBIS and large battery are the key advantages over the A6400. The A6700's AI AF is the reason to pay more.