I found some references to new devices in the Watchguard website. Is there a release date for these new models?
Production planning for tabletop devices is roughly every 3 years or so. None of these devices have a release date quite yet. As it takes awhile to decide on specs for new devices and work out manufacturing, planning often starts before the current models are released.
If you're interested in seeing (or possibly even previewing new devices) I'd suggest watching the beta site at watchguard.centercode.com. Active contributors are often invited into hardware betas and get to test new products if selected.
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