Some web sites are reporting that Panasonic is set to unveil a 20" 4K OLED tablet at the IFA 2013 event next week. Those sites are relying on auto-translated Japanese text. But in fact the company will not show such a tablet. In an English PR, Panasonic says they will show a 4K 20" tablet and a 4K OLED panel prototype - those are two different devices.
I'm guessing Panasonic's 4K OLED panel will be the same 56" 4K (3840x2160) OLED TV panel shown at CES 2013. This panel was made using an "all-printing" method. Sumitomo Chemical revealed that this TV prototype used the company's PLED materials. Panasonic's panel uses a substrate (probably Oxide-TFT) provided by Sony (which are actually made by AU Optronics) - as part of the two companies collaboration.
It is actually too early to expect OLED product announcements from Panasonic. According to the latest reports, they only plan to start OLED production at around 2015.