iPhone 6,1 and iOS 7 references reportedly appeared in app developer logs using an IP address leading back to Apple’s Cupertino campus. But that doesn't necessarily mean that its the iPhone 6, it could very well be the iPhone 5s and here is why.
There was a full model jump in those developer IDs between the 4 and the 4S - because developer IDs aren't tightly tied to the marketing names of devices. The iPhone 5 is identified as “iPhone5,1″ or “iPhone 5,2″ in developer logs, depending on the model.
From what the developer logs show - it's more likely that we will see the Apple iPhone 5s this summer. But rather its the iPhone 5s or the iPhone 6 - Apple is busy working on the next version of the iPhone even though we just got the iPhone 5!