The details
This answer covers the new-style Gaggia Classic sold from 2018 onward: the Classic Pro (2019), and the Classic Evo Pro revisions from 2023 onward. Older Classics use different kits, covered below.
- Shades of Coffee (the MrShades kit) sells Classic Pro kits with everything included: controller, sensors, wiring and machine-specific instructions. Their current kits list compatibility with the Pro, 2019, and Evo 2023 and later revisions, with single-display and dual-display versions.
- Auber Instruments KIT-GGP fits the Classic Pro from the 2018/2019 redesign onward, in both the standard and European versions. Match the model number on your machine's sticker against Auber's compatibility list before ordering. It adds a pre-infusion timer with pump control on top of brew and steam temperature control.
- Both kits replace thermostat-based temperature cycling with a steady setpoint, which is the entire point: the stock machine's brew temperature swings widely between thermostat clicks.
- The DIY alternative is Gaggiuino, an open-source build that adds pressure profiling as well, but it is a project, not a kit with support.
Confirm your variant before ordering
The single most important step is identifying which Classic you own, because kits are wired for specific generations. Check the model sticker on the underside or rear of the machine. The Classic Pro and Evo generations covered here are the machines sold new from 2018 onward. If your machine is a 2015 to 2018 Classic or an older pre-2015 Classic, it uses a different internal layout and needs a different kit: both Shades of Coffee and Auber sell versions for the older generations, matched by model number, and Auber specifically notes the 2015 European revision needs a different kit than the KIT-GGP. If you bought the machine used and cannot date it, the model number on the sticker is the reliable identifier, not the paint color or badge.
What owners actually do
The owner-community consensus is that the PID is the single highest-value mod on this machine, usually installed alongside a spring or adjusted OPV to bring brew pressure down to the conventional nine-bar range. Shades of Coffee is the default recommendation in UK and EU communities, Auber in North America, largely for shipping reasons rather than quality differences. Installation is screwdriver-and-spade-connector work following step-by-step photo instructions. No soldering is required for either mainstream kit, and a careful first-timer typically finishes in an afternoon.
The trap to avoid
Two traps. First, buying a generic PID controller off a marketplace listing and expecting it to be a kit: a bare controller lacks the machine-specific relay, sensor placement and wiring harness, and that gap is exactly what the packaged kits solve. Second, ordering an older-Classic kit for a Pro or the reverse. The generations differ internally, and the vendors sell separate kits for each. Opening the machine also involves mains wiring, so unplug it and work dry, and expect any warranty position to change once you modify it.