Shoppers who order the popular wireless earbuds from Apple’s online store today will get them on Jan. 5, at the earliest, and only if they pay extra for express shipping. People who use free shipping will receive their AirPods on Jan. 9.

As tech news site 9to5Mac notes, third-party retailers like Best Buy and Verizon show similar messages indicating that AirPods are currently out of stock and are available for shipping only after the new year.

The fact that new AirPods are in short supply highlights the earbuds’ popularity (or their limited production).

KGI Securities analyst Ming-Chi Kuo predicted in a research note in December that Apple’s AirPods shipments would double in 2018 to 26 million to 28 million units. Apple has not disclosed how many AirPods it has sold.

Apple (AAPL) debuted the AirPods, which cost $159, a year ago after a two-month delay. Unlike conventional earbuds, AirPods do not need a wire to connect with smartphones or digital music players.

Apple’s latest iPhones do not include traditional headphone jacks, but instead come with Lightning ports. Therefore, people who own conventional earbuds must use a dongle to connect them to the Lighting jacks.

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Apple shares were up 1.80% in midday trading to $177.10.