https://wccftech.com/galaxy-s21-ultras-s-pen-model-number-leaked-will-be-sold-separately/

We are currently aware that the Galaxy S21 Ultra will have full support for an S-Pen, which will make it the first phone in the history of Galaxy S devices to have the support and functionality. However, Samsung will not include the S-Pen in the box as it will be sold as an additional accessory, which you can buy if you wish to. This also means that the phone will not have a slot for an S-Pen, but 1st and 3rd party manufacturers will release cases with the slot for the S-Pen.

We have heard a lot about the devices so far, but nothing much has been revealed about the S-Pen that Samsung will be releasing for the Galaxy S21 Ultra. Well, that changes today, as we have the model number of the S-Pen that Samsung will be making for the phone.