Proposal #54880, accepted last week, seeds math/rand randomly at startup. Part of the rationale is that programs that expect a specific determinstic sequence from the global rand functions (like rand.Int) are inherently fragile, since any package can change the number of times it calls those functions, which changes the results from all future calls by other packages. So programs should not depend on any kind of determinism from them.

For the same reason, I suggest we deprecate math/rand.Seed (the global seeder). Programs that need a specific deterministic sequence can do that more reliably using NewRand(NewSource(seed)), which they can be sure no other packages are consuming values from.