Startup communities often develop informal traditions that help create a shared identity across cohorts. Recently, some YC founders noticed that the Spring batch previously labeled “X25” on Bookface appears to have been renamed “P25.”

YC has historically used different batch naming conventions over time (for example W25, S24, F23, and more recently X-year labels on Bookface). However, YC has not publicly explained the meaning of these letters or the reason for the change from X25 to P25.

Because many founders had already started referring to the batch as X25, the change has caused some confusion within the community. For founders who identified with the earlier label, the sudden switch may feel like a break in continuity with how the cohort had been referenced.

If there is a reason behind the naming update, greater clarity from YC could help reduce confusion. In the meantime, some founders are expressing a preference for keeping the X25 naming that had already been widely adopted within the cohort.