The Pythagorean theorem is one of the most important mathematical concepts, yet it poses a problem in learning. It is proven that students’ mathematical creative thinking abilities related to this material are still low. There have been quite a few studies on the Pythagorean theorem, but not many have focused on learning development. Therefore, this research aims to optimize students’ mathematical creative thinking abilities through the development of open-ended problem-solving-based differentiated learning. The research design used for development was the Plomp model. The subjects in this study were thirty junior high school students, three mathematics education experts, and one mathematics teacher. The instruments used were an expert validation sheet, a learning response questionnaire, and a mathematical creative thinking ability test. Data was analyzed by combining qualitative and quantitative data analysis. The research findings revealed that open-ended problem-solving-based differentiated instruction was capable of optimizing students’ mathematical creative thinking abilities in learning. This was because differentiated learning facilitated cognitive diversity with various new and creative strategies when solving problems, making learning more meaningful. This research recommended that students be given more opportunities to explore strategies when solving problems.