Software startups are responsible for fast product delivery to the market. To aid this process, a retrospective inside a startup team can be very fruitful for software development. The traditional way of conducting agile retrospectives involves discussion based on what went well, what did not go well, and how to improve the software development cycle helps to save resources, get directed toward the startup vision, and overcome several challenges. To attain insights about the agile retrospective approach in startups, we studied the following question: How are software startups performing agile retrospectives? Hence, we conducted seven multiple case studies with 19 semi-structured interviews that lasted 30–65 min. The results outline that all software startups prefer a reflection through agile retrospectives but not in the traditional manner. Due to the startup’s casual and less restricted working environment, teams prefer informal agile retrospectives, which involve no confined boundaries of time, venue, and participants.