Adobe Source

Source Serif has recently been upgraded to version 4.004 and now includes display, caption and Subheading versions

A note for those who would want to use this superfamily: in the current iteration (Source Sans 3 and Source Serif 4), the vertical metrics of Source Sans match those of Source Serif Small Text, but not those of Source Serif no-qualifier. https://x.com/riccard0/status/1383471618698055682

From Frank Grießhammer (Source Serif’s designer):

Source Serif/Sans are friends, but they do not stem from the same source material. Consequently (and deliberately), the relationship is loose. We are doing our best to make sans/serif work together, while making some decisions to benefit the individual styles.