This study explores the role of ChatGPT in enhancing vocabulary learning among high school students in Kazakhstan. Twenty-seven students participated in a two-week intervention that utilized ChatGPT within a mixed-methods framework. Data were collected through vocabulary assessments administered before and after the intervention, learner surveys at both stages, ChatGPT interaction logs, and follow-up interviews. The tests results were analyzed using a paired t-test. The findings revealed that the students engaged with ChatGPT in strategic and diverse ways, such as adjusting prompt difficulty, requesting translations or definitions, and exploring creative tasks. Many also demonstrated autonomies by generating their own prompts beyond the provided set. A statistically significant improvement in vocabulary scores was observed after the intervention. Students reported highly positive perceptions of ChatGPT, citing its constant availability, adaptive feedback, and flexibility in meeting individual learning needs. Although some technical challenges, like unstable internet connections, were noted, these issues were external to the tool itself. Overall, the study suggests that ChatGPT can be as a flexible and responsive resource for supporting vocabulary development and fostering learner autonomy in EFL contexts. This study also discusses limitations and pedagogical implications.