For years now, Sony has been iterating its mirrorless line of cameras one tiny tweak at a time. That continues with the A5100, a minor variation on the company's existing line.
The A5100 replaces the NEX-5T, Sony's current mid-range mirrorless shooter. It's the last of the Sony cameras. It's also a very minor upgrade over the existing A5000, which inherits that camera's body design, but adds the more advanced image sensor from the A6000.
The A5000 is a teeny tiny little guy—the smallest APS-C interchangeable-lens camera out there, but it didn't have the snappy hybrid autofocus system that's being used by many cameras these days. That changes now because the A5100 gets the 24.3-megapixel APS-C sense with combined phase and contrast autofocus detection.
The camera will be available from mid-September priced at £420 body only, around £550 with the 16-50mm lens kit, and £760 with the 16-50mm + 55-210mm lens kit.
If it feels like all of these mirrorless cameras are starting to blend together a bit, you're right. This is a very minor upgrade. Sony's inexpensive mirrorless line has been excellent. That's nothing new.