The four names, and when each was used
- McKinsey Solve is the current official name. It's what your invitation email and McKinsey's careers page call it.
- Problem Solving Game (PSG) was the common name around 2020 to 2022, used by McKinsey material and by candidates. You'll still see "PSG" in forum threads and in the names of some prep companies.
- McKinsey Digital Assessment is an older label McKinsey itself used, and the phrase still appears in the URL of McKinsey's own Solve page.
- Imbellus game or Imbellus test names the company that built the original version. Prep sites report Imbellus was acquired by Roblox in 2021, after which the assessment continued under McKinsey's own name.
Before all of these there was the Problem Solving Test (PST), a written multiple-choice test. Prep sites report it was replaced by the game-based assessment from around 2019. If a resource is about the PST, it's about a different test entirely.
The games changed more than the name did
This is the part that matters for preparation. The name is cosmetic; the games are not, and they've turned over almost completely.
- Ecosystem Building was the centrepiece of the Imbellus and PSG era: build a food chain of species that survives in a location. It was dropped from the live assessment during 2025. Most YouTube walkthroughs and a lot of written guides are still about it.
- Plant Defense, a tower-defence style game, was the other Imbellus-era game. Prep sites report it was replaced by the Red Rock Study in 2023.
- Red Rock Study arrived in 2023: data analysis in three one-way phases plus six cases. Still on the test. Guide.
- Sea Wolf (the ocean cleanup game) was added in 2024, described by one prep site as the successor to an earlier Ocean Cleanup scenario. Still on the test. Guide.
- Sustainable Futures Lab arrived in March 2026, and a redesigned version was reported in September 2026. Guide.
So a candidate who prepares from an "Imbellus" guide is likely to spend their week on Ecosystem Building and Plant Defense and walk into Red Rock and Sea Wolf cold. Check the date on anything you read. For the current games, use material from 2025 or later, and for the Sustainable Futures Lab, from 2026.
About the "Imbellus cheat sheet"
People search for one. There isn't one that works, for two reasons. First, the content rotates: the island, the packs, the microbes, the numbers and the scenario themes are different between candidates, so a sheet of answers is a sheet of someone else's answers. Second, McKinsey's rules for the assessment ban applications, websites, AI tools and pre-prepared notes during the test, and say breaking them can end your candidacy.
What does transfer from one sitting to the next is structural: Red Rock's phases lock one way and the questions are built around six specific traps; Sea Wolf scores the average of three microbes, not each one; the Sustainable Futures Lab rewards consistency. That's what to learn, and it's what the Solve guide and the three game guides cover, free.
What's still true from the old guides
Not everything ages badly. The general advice survives: read the whole screen before acting, don't do arithmetic in your head when there's a tool for it, pace yourself across the whole game rather than perfecting the first part, and commit to answers instead of flipping. The observation that the assessment records how you work as well as what you answer also dates from the Imbellus era and is still widely reported. Everything about specific games, timings and question counts should be checked against a current source, starting with your own invitation email.
FAQ
Is the McKinsey Imbellus test the same as McKinsey Solve?
Yes. Imbellus was the company that built the original version of the assessment. "Imbellus test" and "Imbellus game" are older names for what McKinsey now calls Solve. The games inside it have changed since then.
What is the McKinsey PSG?
PSG stands for Problem Solving Game, the name McKinsey and candidates used for the assessment around 2020 to 2022, before it was renamed Solve. Same test, older name.
Is there a McKinsey Imbellus cheat sheet?
Not one that works. The scenarios, numbers and microbes rotate between candidates, and McKinsey's rules ban notes, apps, websites and AI tools during the test. What does transfer is knowing the structure of each game and the handful of traps the questions are built around, which is what the guides on this site cover.
Which old Imbellus or PSG guides are still useful?
Anything about the Ecosystem Building game or Plant Defense describes games that are no longer on the test. Advice about reading carefully, pacing and not thrashing still applies. For the current games (Red Rock Study, Sea Wolf, Sustainable Futures Lab) use material dated 2025 or later.
What was the McKinsey PST?
The Problem Solving Test, a written multiple-choice test McKinsey used before the game-based assessment. Prep sites report it was replaced by the Imbellus game from around 2019. If a resource is about the PST, it's about a different test.
Keep going
Start with the McKinsey Solve guide for the current format and what your invitation length means, then the Red Rock Study guide and the Sea Wolf guide. The retired Ecosystem game is still on the site as a reasoning drill, clearly labelled as legacy.
SolveForge is an independent practice tool and is not affiliated with, endorsed by, or connected to McKinsey & Company. "McKinsey" and "Solve" are trademarks of their respective owners. Practising here does not guarantee any assessment result.