When did Russian begin? There is no single birthday
The language changed over centuries, from shared Slavic ancestors to modern Russian. No one date marks its birth.
How Slavic languages changed
Schenker's The Dawn of Slavic connects Slavic settlement and migration, the development of the language from its Indo-European origins, and the beginnings of Slavic writing in Old Church Slavonic. The research record models Proto-Slavic as a long reconstructed continuum rather than a dated event. Yale University Press ↗
A family of living languages
The Slavonic Languages, edited by Comrie and Corbett, treats each living Slavic language and the extinct Old Church Slavonic and Polabian with the same structure: history, phonology, grammar, dialects. It is the reference used here for classification. Routledge ↗
The wider branch
Kapović's survey of the Indo-European languages includes a Balto-Slavic section, which is where the record places the ancestor shared with Baltic. Old East Slavic is kept as a conventional cover term for medieval varieties, and modern Russian as a gradual emergence rather than a single-date birth. Routledge ↗
What do early Slavic texts reveal?
If the first written Slavic is Old Church Slavonic, a liturgical language, what can and cannot it tell you about how people spoke in Kyiv or Novgorod?