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The KSTAR ECH system has been upgraded to ensure steady-state advanced operation of KSTAR. The planned ECHs include a total of six 1 MW, 300 s ECH systems, of which four 105/140 GHz dual frequency systems have been commissioned and are being used in KSTAR experiments. Additionally, a 170 GHz Russian gyrotron has been commissioned and is ready for injection. The final unit, a multifrequency gyrotron similar to Japan's ITER gyrotron, is scheduled for installation and operation in early 2025. To achieve the KSTAR mission of high-performance long-pulse operation using a plasma operation scenario with a high poloidal beta, ECH requires stable and long pulses, which typically results in the reduction of ECH power during campaigns. Consequently, one ECH unit with power ranging from 0.5 to 0.7 MW was utilized in the KSTAR experiments. The ECH power and launching angle can be controlled by the Plasma Control System (PCS) which maximizes the ECH effect at startup and at the flat top of the discharge. This paper describes the development status of the KSTAR ECH system and reports the longpulse operation results of the ECH system for a dummy load and KSTAR. [ABSTRACT FROM AUTHOR]