Session types are a rich type discipline, based on linear types, that
lift the sort of safety claims that come with type systems to
communications. However, web-based applications and micro services
are often written in a mix of languages, with type disciplines in a
spectrum between static and dynamic typing. Gradual session types
address this mixed setting by providing a framework which grants
seamless transition between statically typed handling of sessions and
any required degree of dynamic typing.

We propose GradualGV as an extension of the functional session type
system GV with dynamic types and casts. We demonstrate type and
communication safety as well as blame safety, thus extending previous
results to functional languages with session-based communication. The
interplay of linearity and dynamic types requires a novel approach to
specifying the dynamics of the language.