Connecting to postgres cloudsql DB over unix socket not working

Im following the docs, but this is not working. I'm trying to connect to a postgres cloudsql instance using the proxy with google IAM auth.

Im doing this over a unix socket to workaround the tcp issue where it hangs

Starting the proxy works:

# Create a local folder for socket
sudo mkdir cloudsql; sudo chmod 777 cloudsql
# Start the proxy
./cloud_sql_proxy -dir=./cloudsql -instances=myproject:us-central1:mydb

It tells me its listening:

2021/05/03 13:01:36 Rlimits for file descriptors set to {Current = 8500, Max = 9223372036854775807}
2021/05/03 13:01:37 Listening on cloudsql/myproject:us-central1:mydb/.s.PGSQL.5432 for myproject:us-central1:mydb
2021/05/03 13:01:37 Ready for new connections

Now trying to connect to it. All of these command result in the same error: psql: error: could not translate host name "NAME" to address: nodename nor servname provided, or not known

psql "sslmode=disable host=cloudsql/mydb"
psql "sslmode=disable host=cloudsql/myproject:us-central1:mydb"
psql "sslmode=disable host=myproject:us-central1:mydb"

What am I doing wrong here?