Nowadays bioactive glasses are diffused in medical practice due to their excellent bioactivity. However high temperature treatments, which are commonly required in several processing routes, may induce the glass to crystallize into a glass-ceramic, with possible negative effects on its bioactivity. In this work a new bioactive glass composition, inspired by the widely used Bioglass® 45 S5, was formulated by increasing the calcium content and substituting the sodium oxide with potassium oxide. The novel glass can be treated at a relatively low temperature (800 °C) and it is characterized by a reduced tendency to crystallize with excellent effects in terms of bioactivity, according to in vitro tests. Therefore, the new composition opens intriguing scenarios whenever a thermal treatment is required to apply or to sinter the glass, such as in the production of scaffolds or the deposition of coatings.