I’m guessing it’s not really a M3.

No M3 has thunderbolt 5.

This is a new chip with M3 marketing. I’d expect this from Intel, not Apple.

Baseline M4 doesn't have Thunderbolt 5 either; only the Pro/Max variants do.

The press-release even calls TB5 out: >Each Thunderbolt 5 port is supported by its own custom-designed controller directly on the chip.

Given that they're doing the same on A-series chips (A18 Pro with 10Gbps USB-C; A18 with USB 2.0); I imagine it's just relatively simple to swap the I/O blocks around and they're doing this for cost and/or product segmentation reasons.

Which means this is a whole new chip. It may be M3 based, but with added interposer support and new thunderbolt stuff.

Which, at this point, why not just use M4 as a base?

>Which, at this point, why not just use M4 as a base?

I imagine that making those chips is quite a bit more involved than just taking the files for M3 Max, and copy-pasting them twice into a new project.

I imagine it just takes more time to design/verify/produce them; especially given they're not selling very many of them, so they're probably not super-high-priority projects.

Could be that M4 requires a different TSMC fab that is at full production doing iPhones.

Or they are saving the M4 Ultra name for later on ...

TB 5 seems like the sort of thing you could 'slap on' to a beefy enough chip.

Or the sort of thing you put onto a successor when you had your fingers crossed that the spec and hardware would finalize in time for your product launch but the fucking committee went into paralysis again at the last moment and now your product has to ship 4 months before you can put TB 5 hardware on shelves. So you put your TB4 circuitry on a chip that has the bandwidth to handle TB5 and you wait for the sequel.

Sounds like you’ve seen some things.

The world is full of features that didn't make the cutoff for launch date. I believe there's one or two of these publicly known in Apple's history, but it's an old tale.