IDC estimate Steam Deck has sold ~4 million units, total handheld PC market 6 million

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It will be interesting to see what it sells lifetime, and if the Switch 2 has any impact on it; I suspect a lot of Steam Deck's sales came from people who wanted to play on the go with games/graphics that the current Switch couldn't handle, so a successor that's more powerful and can run modern AAA titles might have more overlap.