but does it have a REPL?
Lots of BEAM's runtime interaction capability is lost without one.
Gleam can be used from the Erlang REPL easily, there's no additional runtime/overhead or complex translation between the two languages.
I would definitely bet my start up on Gleam!
Bringing static typing to the BEAM is like a dream come true!
It's a young language to be sure, but I see the potential. (Maybe don't bet your startup on it.)