Microchip PIC32 microcontroller.
This is the first chip we've seen with a microAptiv core and Microchip's most powerful MCU to date, presumably intended to give STM32 a run for its money.
It's brand new, to the point that Microchip's website still shows it as “future product” and it's not sold on anything but dev boards. We just wanted process info so the rather serious errata were a non-issue.
Looks like a 130 nm copper process, probably 6-metal. Fill pattern looks like TSMC.
Size is approximately 5800 x 5500 μm (31.9 mm2)
Power distribution wiring
Top left corner showing standard TSMC fill patterns
Long shot of mask rev markings
Closeup of mask rev markings. Looks like five copper layers and one thick aluminum layer.