For decades, studies have revealed students' decreasing interest in science. Extracurricular learning opportunities--the Science Olympiads being a publicly well-known example--are an important means identified to tackle this challenge and help students further differentiate their interests. Better understanding the underlying constructs and characteristics of Science Olympiad exams can provide several implications not just for Science Olympiads, but also science education more broadly, for example, with regard to how the competitions' international juries defines expectations for high performance in the life sciences. This study analyzes exams set by the International Biology Olympiad (IBO) as an example for a top-tier international competition in the life sciences. The findings extend previous works on test item characteristics toward student competitions and high-performer education. We conducted a systematic analysis of N = 703 closed-ended and laboratory test items from six IBO assessment years across the competition's history. A categorical framework was developed to analyze items according to four areas: formal characteristics, content and practices, cognitive aspects, and the use of representations. Our findings highlight assessment characteristics used to challenge high-performing students. We derive implications for general life sciences education, as well as for further developing the assessments of Science Olympiads.