HDMI Alt Mode is a variant of USB-C's Alternate Mode that transmits a native HDMI signal over the connector, instead of the more widely implemented DisplayPort signal. Few devices actually include HDMI Alt Mode hardware, since supporting it adds cost without much practical benefit over converting from DisplayPort.
In practice, most USB-C to HDMI cables and adapters on the market work by converting a DisplayPort Alt Mode signal to HDMI inside the adapter, rather than relying on true HDMI Alt Mode from the source device. The end result for the user looks the same, an HDMI plug that fits a television or monitor, but the underlying technology differs.
Because HDMI Alt Mode support is rare and hard to confirm from a spec sheet alone, assuming a device uses DisplayPort Alt Mode with a converting adapter is usually the safer approach when buying cables. See our guide to USB video output for practical buying advice.
