I have a 3.5/4.5 exhaust valve in front of me - (A 116 02 (logo)) stamped on it.
I've always believed they were sodium-filled because, if not, their stems would likely be as narrow as the intake valve stems. They are narrow at the top but widen shortly after - most likely for the sodium. IF I were feeling daring I'd cut into it to see - but I will not take that chance, thanks!

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Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k