When Apple promised that new iMacs later in the year would include pro machines, it wasn’t messing around. The new iMac Pro slated for release later this year won’t just be the most powerful iMac Apple has ever made, it will be ‘the most powerful Mac ever.’

That means that Apple’s new all-in-one desktop machine will be faster and more capable than the current version of the standalone Mac Pro.

The specs certainly bear out Apple’s description …

The processor options will range from 8-core to a staggering 18-core. RAM will be configurable to 128GB, storage to 4TB SSD. The standard graphics card will be a Radeon Pro Vega 56, configurable to a Vega 64 with 16GB of HBM2 memory. This will be able to drive the built-in 5K display plus two external ones at 60Hz, each with a billion colors. Alternatively, you can substitute four 4K UHD displays at the same frame-rate.

You get 10GB Ethernet and four USB-C/Thunderbolt 3 ports, in addition to four USB 3 ports and an SDXC card slot.

So if you get these kind of specs from Apple’s all-in-one offering, and it’s promising an all-new Mac Pro machine later, surely that one has to deliver truly incredible performance to remain ahead of the iMac?

Well, maybe – but not necessarily.

The iMac Pro is going to be a phenomenally powerful machine – but it’s not going to be very upgradable. Sure, you’ll be able to hang things off those Thunderbolt 3 ports, including external graphics cards, but it looks like internal upgrades won’t be an option. Not even the RAM.

It’s the upgrade options, not the initial spec, that will distinguish the new Mac Pro. Here’s what Phil Schiller said back in April.

So yes, Apple has promised that it will be the best machine in the line-up, meaning that by definition it has to have a higher spec than the iMac Pro. But perhaps not massively so. What you’ll really be buying with the Mac Pro is two things.

First, configuration options. Four USB-C ports is good, but as the standard takes off, there will be pros who’ll want more – and you’ll be able to add them. Up to 4TB fast SSD is very nice, but again, AV pros will want more, and they’ll be able to add it without having to hang them off the outside of the machine. And so forth. Unlike the iMac, you won’t be buying a sealed unit.

Second, longevity. The iMac Pro will be a stonking spec when it launches, but of course technology never stands still. A blindingly-fast machine today will look distinctly pedestrian a few years down the line. With a modular format, you should be able to simply slot in new components as they become available – including, I’m sure, CPU and GPU.

So sure, expect the new Mac Pro to be a higher spec than the iMac Pro – Apple has promised that much – but don’t necessarily expect it to be in a different league. What you should expect is the ability to configure it to you own needs, and to be able to upgrade it over time.