Version Migration Map
85%MUI is where model training data most likely betrays a React agent: the library has shipped multiple majors since the v5 era that training corpora over-represent, and it renamed or removed exactly the APIs a model reaches for by reflex (Grid item xs, componentsProps, makeStyles, InputProps). This module is a delta, not a MUI tutorial: what changed at each major, which docs to trust for which version, and the traps that compile cleanly and fail at runtime. Read the codebase's lockfile before writing any MUI code. There is no single dialect valid across v5, v6 and v7 — the Grid API alone differs in all three — so the first action on any MUI ticket is package.json/lockfile: the @mui/material major, any @mui/x-* packages and their licensing tier, the React major, and Emotion vs styled-components. Material UI (MUI Core) has never published a version 8. Verified against the npm registry on 2026-08-08 — @mui/material stable majors are 5, 6, 7, 9. Not one 8.x release exists, not even a prerelease; GET registry.npmjs.org/@mui/material/8.0.0 returns HTTP 404. The same 5/6/7/9 gap holds across @mui/system, @mui/icons-material, @mui/styled-engine, @mui/utils and @mui/material-nextjs. MUI say so themselves, in the v9 launch post: "So for v9, we're realigning: Material UI moves from v7 straight to v9 (there is no Material UI v8, like there is no v2), in step with MUI X v9, restoring a single shared major for the suite for the first time since that split." — Introducing Material UI and MUI X v9, 2026-04-08