kubectl create token --duration=0s -n [namespace] [serviceaccountname]
If they made it consistent with kubeadm, then this would set it to never expire. However, I don’t believe in any consistency anymore of Kubernetes 
Because I found this here as well…
–duration=0s Requested lifetime of the issued token. The server may return a token with a longer or shorter lifetime.
Thus, best to set it to some timeframe you feel comfortable with. E.g. 1y via the --duration flag