Sustainable education requires scalable, affordable, and personalized solutions capable of addressing diverse learner needs while reducing dependence on resource -intensive instructional models. This paper presents “SayLess”, a student -developed artificial intelligence (AI) -powered mobil e application designed to support sustainable English language learning through adaptive personalization and learner autonomy. The application integrates AI - driven tools for reading, listening, speaking and writing, enabling real- time content adjustment to users’ proficiency, pace, and progress. The interface was designed in Figma, and the backend architecture was implemented using Visual Studio. The current version is deployed on iOS devices, with planned Android expansion to enhance accessibility. A pilot implementation with university students evaluated usability, engagement, and language development outcomes. Results indicate improvements in motivation, writing accuracy, and independent learning behaviors, alongside reduced reliance on traditional tutori ng. The findings demonstrate that student-led AI innovation can contribute to sustainable educational practices aligned with global sustainable development goals. AI in education, sustainable learning, adaptive systems, mobile learning, personalized Englis h learning, EdTech innovation.