Somewhere in every monitoring app’s design there’s a slot waiting for a GPU temperature. Intel Macs had one: a discrete graphics chip, its own silicon, its own sensor, its own number. Users expect the number. Dashboards have a place for it. And on Apple Silicon, I couldn’t find it. Not because the machine hides it well. Because, as far as I can determine, it isn’t there.
One die, one thermal story
On M-series chips the CPU and GPU aren’t neighbors. They’re roommates on a single piece of silicon, sharing memory, sharing power delivery, and above all sharing heat. My M1 Max exposes eleven separate die-zone thermometers, scattered across that shared silicon, and heavy GPU work shows up in them just as surely as heavy CPU work does. What it does not expose, anywhere I can probe, is a sensor labeled as the GPU’s own. The die zones are the thermal story, for both processors at once.
So what should a monitoring app put in the GPU-temperature slot? There are really only two options. Derive something: pick a die zone, relabel it, present it with more confidence than the hardware offers. Or say plainly that the number doesn’t exist and show the die zones for what they are. Readout does the second. The thermals panel tells you the CPU and GPU share a die and that no separate probe exists, and then shows you all eleven zones, named as what they are.
A dashboard should never be more confident than its sensors.
Undocumented ground
A caveat that doubles as the point: Apple doesn’t document these sensors. Every monitoring app on Apple Silicon, mine included, is reading undocumented keys and deciding what to call them, which is why two apps on the same Mac can disagree about “the CPU temperature.” That’s exactly the environment where invented certainty flourishes, and exactly why Readout shows its work: Readout --probe lists every sensor with both its friendly name and the raw key it came from, so you can audit the labeling yourself.
If a future M-series Mac ships a real GPU probe, Readout will show it; the sensors are discovered from the machine, not from a list I maintain. Until then, the honest answer to “what’s my GPU temperature?” on Apple Silicon is: the same as the die it lives on. Any app that tells you otherwise is answering a different question: where did it get the number?