We all certainly remember what happens when sites doubt Gizmodo’s “reliable sources” — Steve Jobs’ health, anyone? As such, a particularly interesting rumor emerged this morning that Apple tablet hopefuls might want to take note of. Citing “a source that has always been 100% reliable”, Giz claims to have been informed that Apple is currently working on 13-inch and 15-inch tablet models in addition to the 10-inch model that is all but confirmed by now. The source states that two prototypes reminiscent of big aluminum iPhones currently sit in a factory in Shenzuen, China. He or she also claims that at least one is confirmed to be running OS X. The source could not confirm whether these units were prototypes of what will ultimately be production models, or simply demo units of some kind. While it’s known that next month’s Apple event will have absolutely nothing to do with tablets, it might be a pretty safe bet that some kind of tablet announcement might not be far behind.