Apple has begun testing for their new C2 Modem for the next lineup of iPhones, with a leaker sharing information that the C2 Modem is identified with C4020, confirming that the C2 modem does exist but no additional information was provided other than that.
Apple confirmed to the public that iPhone chip development starts years ahead of product launches, so it makes sense that a C2 Modem is already in the making and will surpass the C1 modem, providing a dependable and faster connection for 5G and will potentially be more effective in power efficiency.

Apple stated that the C1 chip built into the iPhone 16e has the highest power efficiency ever for iPhones, allowing for a longer battery life. Speed tests for the C1 modem are pending but it is anticipated that the first modem chip Apple made will be slower than the Snapdragon X71 Qualcomm modem built in other iPhones.