diff --git a/changelog.d/muix-9.md b/changelog.d/muix-9.md
new file mode 100644
index 0000000000..aadc279824
--- /dev/null
+++ b/changelog.d/muix-9.md
@@ -0,0 +1,17 @@
+### Changed
+
+- **MUI X implementations are generated against @mui/x-charts 9.16, React 19
+  and @mui/material 9.5.** The pinned render stack in the root `package.json`
+  moves up from @mui/x-charts 7.29.1, React 18.3.1 and @mui/material 5.18.0,
+  matching the React and Material versions the frontend already runs.
+  `prompts/library/muix.md` gains a "MUI X v9 API" section on the changes that
+  break or silently restyle generated code: `ChartsContainer` instead of
+  `ChartContainer`, `hideLegend` and the new legend position values, the HTML
+  legend's extra height, `position: "none"` instead of `leftAxis={null}`, the
+  per-chart CSS classes and `[data-series]`, and the line-mark defaults. The
+  Sizing section adds that each axis needs an explicit `height` or `width` once
+  its fonts grow, because v9 truncates tick labels that don't fit its band.
+  The render harness itself needed no change. Existing MUI X implementations
+  were written for v7: 164 of 323 no longer bundle under v9, and most of the
+  rest render differently, so they need regeneration before they can be
+  re-rendered. (#12243)
diff --git a/package-lock.json b/package-lock.json
index ae09298e0a..cd77b5323c 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,14 +11,14 @@
       "dependencies": {
         "@emotion/react": "11.14.0",
         "@emotion/styled": "11.14.1",
-        "@mui/material": "5.18.0",
-        "@mui/x-charts": "7.29.1",
+        "@mui/material": "9.5.0",
+        "@mui/x-charts": "9.16.0",
         "chart.js": "4.4.7",
         "d3": "7.9.0",
         "echarts": "6.1.0",
         "highcharts": "13.1.1",
-        "react": "18.3.1",
-        "react-dom": "18.3.1"
+        "react": "19.3.1",
+        "react-dom": "19.3.1"
       },
       "devDependencies": {
         "esbuild": "0.28.1",
@@ -167,6 +167,28 @@
         "node": ">=6.9.0"
       }
     },
+    "node_modules/@base-ui/utils": {
+      "version": "0.5.0",
+      "resolved": "https://registry.npmjs.org/@base-ui/utils/-/utils-0.5.0.tgz",
+      "integrity": "sha512-dYGGcEttjkYiMoa5nHm8vLaJ2UcuTWxo3BFAwOYXeRg/q7UVVvA6cacEIXEs3FgBfK1CGtW1ptElqs7wsx+t9A==",
+      "license": "MIT",
+      "dependencies": {
+        "@babel/runtime": "^7.29.7 || ^8.0.0",
+        "@floating-ui/utils": "^0.2.12",
+        "reselect": "^5.3.0",
+        "use-sync-external-store": "^1.7.0"
+      },
+      "peerDependencies": {
+        "@types/react": "^17 || ^18 || ^19",
+        "react": "^17 || ^18 || ^19",
+        "react-dom": "^17 || ^18 || ^19"
+      },
+      "peerDependenciesMeta": {
+        "@types/react": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/@emotion/babel-plugin": {
       "version": "11.13.5",
       "resolved": "https://registry.npmjs.org/@emotion/babel-plugin/-/babel-plugin-11.13.5.tgz",
@@ -755,6 +777,12 @@
         "node": ">=18"
       }
     },
+    "node_modules/@floating-ui/utils": {
+      "version": "0.2.12",
+      "resolved": "https://registry.npmjs.org/@floating-ui/utils/-/utils-0.2.12.tgz",
+      "integrity": "sha512-HpCo8tmWzLVad5s2d19EhAz5zqrrQ6s69qd6moPMQvkOuSwDT1YgRfWSVuc4ennqrgv3OHppiOGMQ7oC13yIww==",
+      "license": "MIT"
+    },
     "node_modules/@jridgewell/gen-mapping": {
       "version": "0.3.13",
       "resolved": "https://registry.npmjs.org/@jridgewell/gen-mapping/-/gen-mapping-0.3.13.tgz",
@@ -797,9 +825,9 @@
       "license": "MIT"
     },
     "node_modules/@mui/core-downloads-tracker": {
-      "version": "5.18.0",
-      "resolved": "https://registry.npmjs.org/@mui/core-downloads-tracker/-/core-downloads-tracker-5.18.0.tgz",
-      "integrity": "sha512-jbhwoQ1AY200PSSOrNXmrFCaSDSJWP7qk6urkTmIirvRXDROkqe+QwcLlUiw/PrREwsIF/vm3/dAXvjlMHF0RA==",
+      "version": "9.5.0",
+      "resolved": "https://registry.npmjs.org/@mui/core-downloads-tracker/-/core-downloads-tracker-9.5.0.tgz",
+      "integrity": "sha512-PErEpl3Lp+1ZqWYKI7GQU8XSiciAFmLbUAZ7IoaUL598HLy1UAFuEUMEJu8yAS1v8vkXYzWprMVZzky4UwXoOA==",
       "license": "MIT",
       "funding": {
         "type": "opencollective",
@@ -807,26 +835,26 @@
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     },
     "node_modules/@mui/material": {
-      "version": "5.18.0",
-      "resolved": "https://registry.npmjs.org/@mui/material/-/material-5.18.0.tgz",
-      "integrity": "sha512-bbH/HaJZpFtXGvWg3TsBWG4eyt3gah3E7nCNU8GLyRjVoWcA91Vm/T+sjHfUcwgJSw9iLtucfHBoq+qW/T30aA==",
+      "version": "9.5.0",
+      "resolved": "https://registry.npmjs.org/@mui/material/-/material-9.5.0.tgz",
+      "integrity": "sha512-QgqvdVjZoKxP8E8SBxYY6LrdV+kw00moXweZQWBbMMdifPKZAGfUaaXhGKIca6fjKnCL6HJIe/AWWCpqNvyHVw==",
       "license": "MIT",
       "dependencies": {
-        "@babel/runtime": "^7.23.9",
-        "@mui/core-downloads-tracker": "^5.18.0",
-        "@mui/system": "^5.18.0",
-        "@mui/types": "~7.2.15",
-        "@mui/utils": "^5.17.1",
+        "@babel/runtime": "^7.29.7 || ^8.0.5",
+        "@mui/core-downloads-tracker": "^9.5.0",
+        "@mui/system": "^9.5.0",
+        "@mui/types": "^9.5.0",
+        "@mui/utils": "^9.5.0",
         "@popperjs/core": "^2.11.8",
-        "@types/react-transition-group": "^4.4.10",
-        "clsx": "^2.1.0",
-        "csstype": "^3.1.3",
+        "@types/react-transition-group": "^4.4.12",
+        "clsx": "^2.1.1",
+        "csstype": "^3.2.3",
         "prop-types": "^15.8.1",
-        "react-is": "^19.0.0",
+        "react-is": "^19.3.0",
         "react-transition-group": "^4.4.5"
       },
       "engines": {
-        "node": ">=12.0.0"
+        "node": ">=14.0.0"
       },
       "funding": {
         "type": "opencollective",
@@ -835,6 +863,7 @@
       "peerDependencies": {
         "@emotion/react": "^11.5.0",
         "@emotion/styled": "^11.3.0",
+        "@mui/material-pigment-css": "^9.5.0",
         "@types/react": "^17.0.0 || ^18.0.0 || ^19.0.0",
         "react": "^17.0.0 || ^18.0.0 || ^19.0.0",
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@@ -846,104 +875,7 @@
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-      "resolved": "https://registry.npmjs.org/@mui/private-theming/-/private-theming-5.17.1.tgz",
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-      "license": "MIT",
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-        "@mui/utils": "^5.17.1",
-        "prop-types": "^15.8.1"
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-        "node": ">=12.0.0"
-      },
-      "funding": {
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-        "url": "https://opencollective.com/mui-org"
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-      "resolved": "https://registry.npmjs.org/@mui/styled-engine/-/styled-engine-5.18.0.tgz",
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-        "@mui/private-theming": "^5.17.1",
-        "@mui/styled-engine": "^5.18.0",
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-        "@mui/utils": "^5.17.1",
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-      },
-      "peerDependenciesMeta": {
-        "@emotion/react": {
-          "optional": true
-        },
-        "@emotion/styled": {
+        "@mui/material-pigment-css": {
           "optional": true
         },
         "@types/react": {
@@ -952,14 +884,13 @@
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+      "version": "9.5.0",
+      "resolved": "https://registry.npmjs.org/@mui/private-theming/-/private-theming-9.5.0.tgz",
+      "integrity": "sha512-UHZKySlr4ZJeA5HEhe/Tq1fhsR5573ViKYn7JV80dCVJtgqRQIplRSer1DHPg2Yi22llX7QRhgM0Vtrx4kZHSA==",
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-      "peer": true,
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-        "@babel/runtime": "^7.28.6",
-        "@mui/utils": "^7.3.11",
+        "@babel/runtime": "^7.29.7 || ^8.0.5",
+        "@mui/utils": "^9.5.0",
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@@ -979,63 +910,13 @@
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+      "version": "9.5.0",
+      "resolved": "https://registry.npmjs.org/@mui/styled-engine/-/styled-engine-9.5.0.tgz",
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@@ -1064,17 +945,16 @@
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+      "resolved": "https://registry.npmjs.org/@mui/system/-/system-9.5.0.tgz",
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-        "@mui/styled-engine": "^7.3.10",
-        "@mui/types": "^7.4.12",
-        "@mui/utils": "^7.3.11",
+        "@babel/runtime": "^7.29.7 || ^8.0.5",
+        "@mui/private-theming": "^9.5.0",
+        "@mui/styled-engine": "^9.5.0",
+        "@mui/types": "^9.5.0",
+        "@mui/utils": "^9.5.0",
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@@ -1104,14 +984,13 @@
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+    "node_modules/@mui/types": {
+      "version": "9.5.0",
+      "resolved": "https://registry.npmjs.org/@mui/types/-/types-9.5.0.tgz",
+      "integrity": "sha512-O0S6xS80qEQqW2CYNrd4GlBEQ1xpMOHZ5b4zO/DaLu6NZmtthM6smEg0Gz/u9gX5vL+8NB3EiBIxmxSCcG590Q==",
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-      "peer": true,
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-        "@mui/types": "^7.4.12",
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+      "version": "0.28.0",
+      "resolved": "https://registry.npmjs.org/scheduler/-/scheduler-0.28.0.tgz",
+      "integrity": "sha512-juorfCmIkIw8tT+p5BXSm6PJjQF/ycEYmKyzURCIt/RaZIhL+PulbQ9Yu2z1HdOJDdqDTlxA1+xKBmHXJsczAw==",
+      "license": "MIT"
     },
     "node_modules/source-map": {
       "version": "0.5.7",
@@ -2467,6 +2297,15 @@
       "integrity": "sha512-N82ooyxVNm6h1riLCoyS9e3fuJ3AMG2zIZs2Gd1ATcSFjSA23Q0fzjjZeh0jbJvWVDZ0cJT8yaNNaaXHzueNjg==",
       "license": "0BSD"
     },
+    "node_modules/use-sync-external-store": {
+      "version": "1.7.0",
+      "resolved": "https://registry.npmjs.org/use-sync-external-store/-/use-sync-external-store-1.7.0.tgz",
+      "integrity": "sha512-6L+EeigHMQhdaIPNIFUKwfWJSwWFQ8gJbJ2DLOs5sDIegTwR9fRxvnM3uciHKjIZhFz+KAv2emhWMRvDmMcY8A==",
+      "license": "MIT",
+      "peerDependencies": {
+        "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0"
+      }
+    },
     "node_modules/yaml": {
       "version": "1.10.3",
       "resolved": "https://registry.npmjs.org/yaml/-/yaml-1.10.3.tgz",
diff --git a/package.json b/package.json
index cf94bddce9..c000d9a628 100644
--- a/package.json
+++ b/package.json
@@ -14,14 +14,14 @@
   "dependencies": {
     "@emotion/react": "11.14.0",
     "@emotion/styled": "11.14.1",
-    "@mui/material": "5.18.0",
-    "@mui/x-charts": "7.29.1",
+    "@mui/material": "9.5.0",
+    "@mui/x-charts": "9.16.0",
     "chart.js": "4.4.7",
     "d3": "7.9.0",
     "echarts": "6.1.0",
     "highcharts": "13.1.1",
-    "react": "18.3.1",
-    "react-dom": "18.3.1"
+    "react": "19.3.1",
+    "react-dom": "19.3.1"
   },
   "devDependencies": {
     "esbuild": "0.28.1",
diff --git a/prompts/library/muix.md b/prompts/library/muix.md
index 0f3ca53062..819aededa0 100644
--- a/prompts/library/muix.md
+++ b/prompts/library/muix.md
@@ -8,7 +8,7 @@ entry: the file extension is **`.tsx`**, `language_id` is **`javascript`**
 **browser render harness** (`node automation/js-render/render.mjs`) via that
 harness's **React (esbuild) branch** — *not* Python, Rscript, or julia.
 
-**API level:** MUI X Charts 7. The root `package-lock.json` pins this major of
+**API level:** MUI X Charts 9. The root `package-lock.json` pins this major of
 `@mui/x-charts`; write against its API.
 
 > ## 🚫 Community surface ONLY — no MUI X Pro / Premium (hard rule)
@@ -63,7 +63,7 @@ export default function Chart() {
   return (
     <BarChart
       width={window.ANYPLOT_SIZE.width}
-      height={window.ANYPLOT_SIZE.height}
+      height={window.ANYPLOT_SIZE.height - 40}   // legend band, see "MUI X v9 API"
       colors={t.palette}
       skipAnimation
       xAxis={[{ scaleType: "band", data: ["Mon", "Tue", "Wed", "Thu", "Fri"] }]}
@@ -101,9 +101,10 @@ gate rejects anything off by more than 16 px and re-triggers repair):
 
 Exact pixels come from Playwright `deviceScaleFactor: 2` over the pre-sized mount
 (1600×900 / 1200×1200 CSS). **Size the chart to `window.ANYPLOT_SIZE`**
-(`width={window.ANYPLOT_SIZE.width} height={window.ANYPLOT_SIZE.height}`) — never
-hard-code other dimensions. For a square spec (pie / radial / heatmap-style),
-put this on its own line at the very top of the file:
+(`width={window.ANYPLOT_SIZE.width} height={window.ANYPLOT_SIZE.height}`, minus
+the legend band when a legend shows) — never hard-code other dimensions. For a
+square spec (pie / radial / heatmap-style), put this on its own line at the very
+top of the file:
 
 ```tsx
 //# anyplot-orientation: square
@@ -117,6 +118,14 @@ space — small numbers like the other JS libs. MUI X defaults are already sized
 for CSS px; only nudge `tickLabelStyle` / `slotProps` font sizes if labels look
 small at the final resolution (axis/legend ≈ 14–16 px, title ≈ 22 px).
 
+Each axis reserves a fixed band for its ticks and title (default 25 px for an x
+axis, 45 px for a y axis), and v9 **truncates tick labels that don't fit — down
+to `0…` or an empty string**. Whenever you enlarge axis fonts or add an axis
+`label`, size the band in the axis config with a number: `height` on x axes
+(e.g. `height: 72`), `width` on y axes (e.g. `width: 84`). Don't rely on
+`"auto"`: in this harness it still truncated at 16–18 px fonts. `margin` is the
+space *outside* the axes, so it no longer has to make room for tick labels.
+
 ## Animation — must be off (static screenshot)
 
 A static PNG must capture the **final** frame, never a half-grown bar. The
@@ -156,7 +165,8 @@ self-contained.
 ## When MUI X can't express the spec
 
 MUI X community covers bar, line, area, pie, scatter, sparkline, gauge, radar,
-funnel, and composed/multi-axis combinations. If the spec's core value is a chart
+and composed/multi-axis combinations; Heatmap, Funnel and Sankey charts are
+Pro-only. If the spec's core value is a chart
 type the **community** surface genuinely can't express (and it isn't a Pro-only
 feature you're tempted to reach for), return **`NOT_FEASIBLE`** with a one-line
 reason — **do not** shell out to Recharts/D3/Chart.js or reach into
@@ -206,7 +216,7 @@ export default function Chart() {
   return (
     <BarChart
       width={window.ANYPLOT_SIZE.width}
-      height={window.ANYPLOT_SIZE.height}
+      height={window.ANYPLOT_SIZE.height - 40}   // legend band, see "MUI X v9 API"
       colors={t.palette}
       skipAnimation
       xAxis={[{ scaleType: "band", data: categories }]}
@@ -235,6 +245,49 @@ export default function Chart() {
 neither has statistics helpers, so short written-out binning, box statistics,
 densities or fits are fine.
 
+## MUI X v9 API — the pinned version
+
+The harness pins **`@mui/x-charts` 9.16 (community), `@mui/material` 9.5 and
+React 19**. Code written for v7 either fails to bundle or silently loses its
+styling, so write against v9:
+
+- **Composition:** `ChartsContainer` from `@mui/x-charts/ChartsContainer`. The
+  v7 `ChartContainer` / `ResponsiveChartContainer`, the
+  `@mui/x-charts/ChartContainer` path and `DefaultChartsLegend` no longer
+  exist, and the bundle fails. A legend is HTML, never part of the SVG: in a
+  composed chart render `<ChartsLegend />` inside `ChartsDataProvider` (wrapped
+  in `ChartsWrapper`) and outside `<ChartsSurface>`.
+- **Legend:** hide it with the chart's `hideLegend` prop (not
+  `slotProps.legend.hidden`). `slotProps.legend.direction` is `"horizontal"` or
+  `"vertical"`; `position` is `{ vertical: "top" | "middle" | "bottom",
+  horizontal: "start" | "center" | "end" }`. Style it with
+  `slotProps.legend.sx` (e.g. `{ fontSize: 16 }`); `labelStyle`,
+  `itemMarkWidth`, `markGap`, `itemGap` and `padding` are gone. The legend adds
+  its own height on top of the chart's `height`, so a visible top or bottom
+  legend needs `height={window.ANYPLOT_SIZE.height - 40}` (or more), or the
+  bottom of the chart is cropped from the PNG.
+- **Axes:** hide an axis with `position: "none"` in its config (the
+  `topAxis` / `leftAxis` / `bottomAxis` / `rightAxis` props are gone); a second
+  y axis takes `position: "right"`. Fonts go through `labelStyle` /
+  `tickLabelStyle` (`labelFontSize` / `tickFontSize` are gone), and the axis
+  band needs `height` / `width` as described under Sizing.
+- **Line charts:** `showMark` defaults to `false`, so set `showMark: true` on a
+  series to draw its dots. Marks cycle through shapes per series; add
+  `shape: "circle"` for uniform dots. The x domain is
+  strict; set `domainLimit: "nice"` on the x axis to pad it to round ticks.
+- **CSS classes are per chart:** `.MuiLineChart-line`, `.MuiLineChart-area`,
+  `.MuiLineChart-mark`, `.MuiBarChart-element`, `.MuiBarChart-label`,
+  `.MuiPieChart-arc`, `.MuiPieChart-arcLabel`, `.MuiScatterChart-marker`. A
+  series is selected by `[data-series="<id>"]`: on the path itself for lines
+  and areas (`'& .MuiLineChart-area[data-series="band"]': { fillOpacity: 0.18 }`),
+  on the series group for bars (`'& [data-series="sales"] .MuiBarChart-element'`).
+  The v7 names (`.MuiAreaElement-root`, `.MuiLineElement-series-<id>`,
+  `.MuiBarElement-root`, `lineElementClasses`, …) match nothing, so that styling
+  silently disappears.
+- **Series:** `id` is a string, unique across all series of the chart.
+  `RadarChart` is stable (no `Unstable_` prefix). `SparkLineChart` takes one
+  `color`, not `colors`.
+
 ## MUI X-Specific Gotchas
 
 - **`export default` is mandatory** — the harness imports the component as the
@@ -247,5 +300,5 @@ densities or fits are fine.
 - Tooltip / hover highlighting is interactive-only and won't appear in the static
   PNG — that's expected; don't force it open for the screenshot.
 - MUI X measures real SVG text (getBBox) for axis/legend layout, which is exactly
-  why the browser harness is used — verify labels aren't clipped at the final
-  resolution and add axis `margin` / `slotProps.legend` spacing if they are.
+  why the browser harness is used — verify labels aren't clipped or truncated at
+  the final resolution and give the axis a larger `height` / `width` if they are.