diff --git a/superset-frontend/packages/superset-ui-chart-controls/src/shared-controls/matrixifyControls.test.ts b/superset-frontend/packages/superset-ui-chart-controls/src/shared-controls/matrixifyControls.test.ts
index 2b007fda917..4efadc18f91 100644
--- a/superset-frontend/packages/superset-ui-chart-controls/src/shared-controls/matrixifyControls.test.ts
+++ b/superset-frontend/packages/superset-ui-chart-controls/src/shared-controls/matrixifyControls.test.ts
@@ -18,6 +18,7 @@
  */
 
 import { isMatrixifyVisible } from './matrixifyControls';
+import type { ControlStateMapping } from '../types';
 
 /**
  * Helper to build a controls object matching the shape used by
@@ -25,7 +26,7 @@ import { isMatrixifyVisible } from './matrixifyControls';
  */
 function makeControls(
   overrides: Record<string, unknown> = {},
-): Record<string, { value: unknown }> {
+): ControlStateMapping {
   const defaults: Record<string, unknown> = {
     matrixify_enable: false,
     matrixify_mode_rows: 'disabled',
@@ -36,7 +37,7 @@ function makeControls(
   const merged = { ...defaults, ...overrides };
   return Object.fromEntries(
     Object.entries(merged).map(([k, v]) => [k, { value: v }]),
-  );
+  ) as ControlStateMapping;
 }
 
 // ── matrixify_enable guard ──────────────────────────────────────────
diff --git a/superset-frontend/packages/superset-ui-chart-controls/src/shared-controls/matrixifyControls.tsx b/superset-frontend/packages/superset-ui-chart-controls/src/shared-controls/matrixifyControls.tsx
index 3e1b331d167..1ec8a340297 100644
--- a/superset-frontend/packages/superset-ui-chart-controls/src/shared-controls/matrixifyControls.tsx
+++ b/superset-frontend/packages/superset-ui-chart-controls/src/shared-controls/matrixifyControls.tsx
@@ -20,7 +20,7 @@
 
 import { t } from '@apache-superset/core/translation';
 import { validateNonEmpty } from '@superset-ui/core';
-import { SharedControlConfig } from '../types';
+import { ControlStateMapping, SharedControlConfig } from '../types';
 import { dndAdhocMetricControl } from './dndControls';
 import { defineSavedMetrics } from '../utils';
 
@@ -29,9 +29,12 @@ import { defineSavedMetrics } from '../utils';
  * Controls for transforming charts into matrix/grid layouts
  */
 
-// Utility function to check if matrixify controls should be visible
+// Utility function to check if matrixify controls should be visible.
+// Controls both visibility callbacks and validator injection via mapStateToProps.
+// The matrixify_enable guard prevents hidden validators from firing on
+// pre-revamp charts with stale matrixify_mode defaults (fix for #38519).
 const isMatrixifyVisible = (
-  controls: any,
+  controls: ControlStateMapping | undefined,
   axis: 'rows' | 'columns',
   mode?: 'metrics' | 'dimensions',
   selectionMode?: 'members' | 'topn' | 'all',
diff --git a/superset-frontend/packages/superset-ui-chart-controls/test/shared-controls/matrixifyControls.test.tsx b/superset-frontend/packages/superset-ui-chart-controls/test/shared-controls/matrixifyControls.test.tsx
new file mode 100644
index 00000000000..f78e6162f47
--- /dev/null
+++ b/superset-frontend/packages/superset-ui-chart-controls/test/shared-controls/matrixifyControls.test.tsx
@@ -0,0 +1,238 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/**
+ * Tests for the matrixify_enable guard in isMatrixifyVisible() and
+ * validator injection via mapStateToProps on real matrixify control definitions.
+ *
+ * These are TDD tests for the fix to apache/superset#38519 regression:
+ * isMatrixifyVisible() must check matrixify_enable before evaluating mode,
+ * otherwise pre-revamp charts with stale matrixify_mode defaults trigger
+ * hidden validators that block save.
+ */
+
+import {
+  matrixifyControls,
+  isMatrixifyVisible,
+} from '../../src/shared-controls/matrixifyControls';
+import type { ControlPanelState, ControlStateMapping } from '../../src/types';
+
+// Helper: build a minimal controls object for ControlPanelState
+const buildControls = (
+  overrides: Record<string, any> = {},
+): ControlStateMapping => {
+  const controls: Record<string, { value: any }> = {};
+  Object.entries(overrides).forEach(([key, value]) => {
+    controls[key] = { value };
+  });
+  return controls as ControlStateMapping;
+};
+
+// Helper: build a minimal ControlPanelState for mapStateToProps.
+// Only provides fields that isMatrixifyVisible and mapStateToProps actually read.
+const buildState = (
+  controlValues: Record<string, any> = {},
+  formData: Record<string, any> = {},
+) =>
+  ({
+    controls: buildControls(controlValues),
+    datasource: { columns: [], type: 'table' },
+    form_data: formData,
+    common: {},
+    metadata: {},
+    slice: { slice_id: 0 },
+  }) as unknown as ControlPanelState;
+
+// ============================================================
+// Validator injection tests via real mapStateToProps (rows)
+// ============================================================
+
+// --- matrixify_dimension_rows ---
+
+test('matrixify_dimension_rows: validators empty when matrixify_enable is falsy', () => {
+  const control = matrixifyControls.matrixify_dimension_rows;
+  const state = buildState(
+    {
+      matrixify_enable: undefined,
+      matrixify_mode_rows: 'dimensions',
+      matrixify_dimension_selection_mode_rows: 'members',
+    },
+    { matrixify_mode_rows: 'dimensions' },
+  );
+
+  const result = control.mapStateToProps!(state, {} as any);
+  expect(result.validators).toEqual([]);
+});
+
+test('matrixify_dimension_rows: validators present when matrixify_enable is true', () => {
+  const control = matrixifyControls.matrixify_dimension_rows;
+  const state = buildState(
+    {
+      matrixify_enable: true,
+      matrixify_mode_rows: 'dimensions',
+      matrixify_dimension_selection_mode_rows: 'members',
+    },
+    { matrixify_mode_rows: 'dimensions' },
+  );
+
+  const result = control.mapStateToProps!(state, {} as any);
+  expect(result.validators.length).toBeGreaterThan(0);
+});
+
+// --- matrixify_topn_value_rows ---
+
+test('matrixify_topn_value_rows: validators empty when matrixify_enable is falsy', () => {
+  const control = matrixifyControls.matrixify_topn_value_rows;
+  const state = buildState(
+    {
+      matrixify_enable: undefined,
+      matrixify_mode_rows: 'dimensions',
+      matrixify_dimension_selection_mode_rows: 'topn',
+    },
+    { matrixify_mode_rows: 'dimensions' },
+  );
+
+  const result = control.mapStateToProps!(state, {} as any);
+  expect(result.validators).toEqual([]);
+});
+
+test('matrixify_topn_value_rows: validators present when matrixify_enable is true', () => {
+  const control = matrixifyControls.matrixify_topn_value_rows;
+  const state = buildState(
+    {
+      matrixify_enable: true,
+      matrixify_mode_rows: 'dimensions',
+      matrixify_dimension_selection_mode_rows: 'topn',
+    },
+    { matrixify_mode_rows: 'dimensions' },
+  );
+
+  const result = control.mapStateToProps!(state, {} as any);
+  expect(result.validators.length).toBeGreaterThan(0);
+});
+
+// --- matrixify_topn_metric_rows ---
+
+test('matrixify_topn_metric_rows: validators empty when matrixify_enable is falsy', () => {
+  const control = matrixifyControls.matrixify_topn_metric_rows;
+  const state = buildState(
+    {
+      matrixify_enable: undefined,
+      matrixify_mode_rows: 'dimensions',
+      matrixify_dimension_selection_mode_rows: 'topn',
+    },
+    { matrixify_mode_rows: 'dimensions' },
+  );
+
+  const result = control.mapStateToProps!(state, {} as any);
+  expect(result.validators).toEqual([]);
+});
+
+test('matrixify_topn_metric_rows: validators present when matrixify_enable is true', () => {
+  const control = matrixifyControls.matrixify_topn_metric_rows;
+  const state = buildState(
+    {
+      matrixify_enable: true,
+      matrixify_mode_rows: 'dimensions',
+      matrixify_dimension_selection_mode_rows: 'topn',
+    },
+    { matrixify_mode_rows: 'dimensions' },
+  );
+
+  const result = control.mapStateToProps!(state, {} as any);
+  expect(result.validators.length).toBeGreaterThan(0);
+});
+
+// ============================================================
+// Validator injection tests via real mapStateToProps (columns)
+// ============================================================
+
+test('matrixify_dimension_columns: validators empty when matrixify_enable is falsy', () => {
+  const control = matrixifyControls.matrixify_dimension_columns;
+  const state = buildState(
+    {
+      matrixify_enable: undefined,
+      matrixify_mode_columns: 'dimensions',
+      matrixify_dimension_selection_mode_columns: 'members',
+    },
+    { matrixify_mode_columns: 'dimensions' },
+  );
+
+  const result = control.mapStateToProps!(state, {} as any);
+  expect(result.validators).toEqual([]);
+});
+
+test('matrixify_dimension_columns: validators present when matrixify_enable is true', () => {
+  const control = matrixifyControls.matrixify_dimension_columns;
+  const state = buildState(
+    {
+      matrixify_enable: true,
+      matrixify_mode_columns: 'dimensions',
+      matrixify_dimension_selection_mode_columns: 'members',
+    },
+    { matrixify_mode_columns: 'dimensions' },
+  );
+
+  const result = control.mapStateToProps!(state, {} as any);
+  expect(result.validators.length).toBeGreaterThan(0);
+});
+
+// ============================================================
+// Direct isMatrixifyVisible guard tests
+// ============================================================
+
+test.each([
+  ['undefined', undefined],
+  ['null', null],
+  ['false', false],
+  ['0', 0],
+])(
+  'isMatrixifyVisible returns false when matrixify_enable is %s',
+  (_, value) => {
+    const controls = buildControls({
+      matrixify_enable: value,
+      matrixify_mode_rows: 'dimensions',
+    });
+    expect(isMatrixifyVisible(controls, 'rows')).toBe(false);
+  },
+);
+
+test('isMatrixifyVisible returns true when matrixify_enable is true and mode matches', () => {
+  const controls = buildControls({
+    matrixify_enable: true,
+    matrixify_mode_rows: 'dimensions',
+  });
+  expect(isMatrixifyVisible(controls, 'rows', 'dimensions')).toBe(true);
+});
+
+test('isMatrixifyVisible returns false when matrixify_enable is true but mode is disabled', () => {
+  const controls = buildControls({
+    matrixify_enable: true,
+    matrixify_mode_rows: 'disabled',
+  });
+  expect(isMatrixifyVisible(controls, 'rows')).toBe(false);
+});
+
+test('isMatrixifyVisible returns true when matrixify_enable is true and any non-disabled mode (no mode filter)', () => {
+  const controls = buildControls({
+    matrixify_enable: true,
+    matrixify_mode_columns: 'metrics',
+  });
+  expect(isMatrixifyVisible(controls, 'columns')).toBe(true);
+});
diff --git a/superset-frontend/src/explore/actions/hydrateExplore.ts b/superset-frontend/src/explore/actions/hydrateExplore.ts
index d488dfb4d29..574707975c2 100644
--- a/superset-frontend/src/explore/actions/hydrateExplore.ts
+++ b/superset-frontend/src/explore/actions/hydrateExplore.ts
@@ -24,7 +24,7 @@ import {
   ExplorePageState,
 } from 'src/explore/types';
 import { getChartKey } from 'src/explore/exploreUtils';
-import { getControlsState } from 'src/explore/store';
+import { getControlsState, handleDeprecatedControls } from 'src/explore/store';
 import { Dispatch } from 'redux';
 import {
   Currency,
@@ -116,6 +116,12 @@ export const hydrateExplore =
         ]),
     );
 
+    // Normalize deprecated controls (e.g., migrate old per-axis matrixify
+    // flags to matrixify_enable) before form_data is stored in Redux state.
+    // getControlsState also calls this on its own copy, but state.form_data
+    // must reflect the same migration so the two stay consistent.
+    handleDeprecatedControls(initialFormData);
+
     const initialExploreState = {
       form_data: initialFormData,
       slice: initialSlice,
diff --git a/superset-frontend/src/explore/store.test.tsx b/superset-frontend/src/explore/store.test.tsx
index 602390a4d4f..d74b5bf0c18 100644
--- a/superset-frontend/src/explore/store.test.tsx
+++ b/superset-frontend/src/explore/store.test.tsx
@@ -17,55 +17,359 @@
  * under the License.
  */
 import { getChartControlPanelRegistry } from '@superset-ui/core';
-import { applyDefaultFormData } from 'src/explore/store';
+import {
+  applyDefaultFormData,
+  getControlsState,
+  handleDeprecatedControls,
+} from 'src/explore/store';
 
-// eslint-disable-next-line no-restricted-globals -- TODO: Migrate from describe blocks
-describe('store', () => {
-  beforeAll(() => {
-    getChartControlPanelRegistry().registerValue('test-chart', {
-      controlPanelSections: [
-        {
-          label: 'Test section',
-          expanded: true,
-          controlSetRows: [['row_limit']],
-        },
-      ],
-    });
-  });
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+(window as any).featureFlags = {};
 
-  afterAll(() => {
-    getChartControlPanelRegistry().remove('test-chart');
-  });
-
-  // eslint-disable-next-line no-restricted-globals -- TODO: Migrate from describe blocks
-  describe('applyDefaultFormData', () => {
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    (window as any).featureFlags = {};
-
-    test('applies default to formData if the key is missing', () => {
-      const inputFormData = {
-        datasource: '11_table',
-        viz_type: 'test-chart',
-      };
-      let outputFormData = applyDefaultFormData(inputFormData);
-      expect(outputFormData.row_limit).toEqual(10000);
-
-      const inputWithRowLimit = {
-        ...inputFormData,
-        row_limit: 888,
-      };
-      outputFormData = applyDefaultFormData(inputWithRowLimit);
-      expect(outputFormData.row_limit).toEqual(888);
-    });
-
-    test('keeps null if key is defined with null', () => {
-      const inputFormData = {
-        datasource: '11_table',
-        viz_type: 'test-chart',
-        row_limit: null,
-      };
-      const outputFormData = applyDefaultFormData(inputFormData);
-      expect(outputFormData.row_limit).toBe(null);
-    });
+beforeAll(() => {
+  getChartControlPanelRegistry().registerValue('test-chart', {
+    controlPanelSections: [
+      {
+        label: 'Test section',
+        expanded: true,
+        controlSetRows: [['row_limit']],
+      },
+    ],
   });
 });
+
+afterAll(() => {
+  getChartControlPanelRegistry().remove('test-chart');
+});
+
+// Helper: build ExploreState for getControlsState
+const buildExploreState = (controlOverrides: Record<string, any> = {}) => ({
+  datasource: { type: 'table' },
+  controls: Object.fromEntries(
+    Object.entries(controlOverrides).map(([k, v]) => [k, { value: v }]),
+  ),
+});
+
+// ============================================================
+// Existing applyDefaultFormData tests
+// ============================================================
+
+test('applyDefaultFormData applies default to formData if the key is missing', () => {
+  const inputFormData = {
+    datasource: '11_table',
+    viz_type: 'test-chart',
+  };
+  let outputFormData = applyDefaultFormData(inputFormData);
+  expect(outputFormData.row_limit).toEqual(10000);
+
+  const inputWithRowLimit = {
+    ...inputFormData,
+    row_limit: 888,
+  };
+  outputFormData = applyDefaultFormData(inputWithRowLimit);
+  expect(outputFormData.row_limit).toEqual(888);
+});
+
+test('applyDefaultFormData keeps null if key is defined with null', () => {
+  const inputFormData = {
+    datasource: '11_table',
+    viz_type: 'test-chart',
+    row_limit: null,
+  };
+  const outputFormData = applyDefaultFormData(inputFormData);
+  expect(outputFormData.row_limit).toBe(null);
+});
+
+// ============================================================
+// Migration tests: handleDeprecatedControls normalizes stale matrixify modes
+// (fix for apache/superset#38519 regression — guards validators AND
+// downstream UI consumers that infer matrixify state from mode values)
+// ============================================================
+
+test('getControlsState resets stale matrixify_mode_rows to disabled when matrixify_enable key absent', () => {
+  const state = buildExploreState();
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_mode_rows: 'dimensions', // stale pre-revamp default
+  };
+
+  const result = getControlsState(state as any, formData as any);
+  const modeControl = result.matrixify_mode_rows as any;
+  expect(modeControl?.value).toBe('disabled');
+});
+
+test('getControlsState resets stale matrixify_mode_columns to disabled when matrixify_enable key absent', () => {
+  const state = buildExploreState();
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_mode_columns: 'metrics', // stale pre-revamp default
+  };
+
+  const result = getControlsState(state as any, formData as any);
+  const modeControl = result.matrixify_mode_columns as any;
+  expect(modeControl?.value).toBe('disabled');
+});
+
+test('getControlsState preserves matrixify mode values when matrixify_enable is true', () => {
+  const state = buildExploreState();
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_enable: true,
+    matrixify_mode_rows: 'dimensions',
+  };
+
+  const result = getControlsState(state as any, formData as any);
+  const modeControl = result.matrixify_mode_rows as any;
+  expect(modeControl?.value).toBe('dimensions');
+});
+
+test('getControlsState preserves matrixify mode values when matrixify_enable is explicitly false', () => {
+  const state = buildExploreState();
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_enable: false,
+    matrixify_mode_rows: 'dimensions',
+  };
+
+  const result = getControlsState(state as any, formData as any);
+  const modeControl = result.matrixify_mode_rows as any;
+  // matrixify_enable key IS present (just false) — migration does NOT fire
+  expect(modeControl?.value).toBe('dimensions');
+});
+
+test('getControlsState is idempotent when matrixify modes already disabled', () => {
+  const state = buildExploreState();
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_mode_rows: 'disabled',
+    matrixify_mode_columns: 'disabled',
+  };
+
+  const result = getControlsState(state as any, formData as any);
+  expect((result.matrixify_mode_rows as any)?.value).toBe('disabled');
+  expect((result.matrixify_mode_columns as any)?.value).toBe('disabled');
+});
+
+test('getControlsState handles form_data with no matrixify keys', () => {
+  const state = buildExploreState();
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+  };
+
+  const result = getControlsState(state as any, formData as any);
+  // Controls should get their defaults — matrixify_mode defaults to 'disabled'
+  expect((result.matrixify_mode_rows as any)?.value).toBe('disabled');
+  expect((result.matrixify_mode_columns as any)?.value).toBe('disabled');
+});
+
+test('getControlsState round-trip: pre-revamp form_data produces no matrixify validation errors', () => {
+  // Simulate a chart saved before #38519 with stale matrixify defaults
+  // Empty controls: on real first-load hydration, no pre-existing controls exist
+  const state = buildExploreState();
+  const preRevampFormData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    // Stale old defaults — no matrixify_enable key (legacy chart)
+    matrixify_mode_rows: 'dimensions',
+    matrixify_mode_columns: 'metrics',
+  };
+
+  const result = getControlsState(state as any, preRevampFormData as any);
+
+  // Every matrixify control should have zero validation errors
+  const matrixifyControlEntries = Object.entries(result).filter(([name]) =>
+    name.startsWith('matrixify_'),
+  );
+  const controlsWithErrors = matrixifyControlEntries.filter(
+    ([, control]) => (control as any)?.validationErrors?.length > 0,
+  );
+
+  expect(controlsWithErrors).toEqual([]);
+});
+
+// ============================================================
+// Dashboard hydration: applyDefaultFormData with stale form_data
+// ============================================================
+
+test('applyDefaultFormData normalizes stale matrixify modes for legacy charts', () => {
+  // Dashboard hydration now runs handleDeprecatedControls too, so stale
+  // matrixify modes from pre-revamp charts are normalized to 'disabled'.
+  // This protects downstream consumers (ChartContextMenu, DrillBySubmenu,
+  // ChartRenderer) that infer "matrixify is active" from mode values alone.
+  const preRevampFormData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_mode_rows: 'dimensions',
+    matrixify_mode_columns: 'metrics',
+    // No matrixify_enable key — legacy chart that never used matrixify
+  };
+
+  const outputFormData = applyDefaultFormData(preRevampFormData as any);
+
+  // Stale values are now normalized to 'disabled'
+  expect(outputFormData.matrixify_mode_rows).toBe('disabled');
+  expect(outputFormData.matrixify_mode_columns).toBe('disabled');
+  expect(outputFormData.matrixify_enable).toBe(false);
+});
+
+// ============================================================
+// P1: Pre-revamp charts that actually used matrixify via old per-axis flags
+// (matrixify_enable_vertical_layout / matrixify_enable_horizontal_layout)
+// ============================================================
+
+test('getControlsState preserves modes and sets matrixify_enable when old vertical flag is true', () => {
+  const state = buildExploreState();
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_enable_vertical_layout: true,
+    matrixify_mode_rows: 'dimensions',
+    matrixify_mode_columns: 'metrics',
+  };
+
+  const result = getControlsState(state as any, formData as any);
+  // Vertical layout was enabled — rows mode preserved, matrixify_enable migrated
+  expect((result.matrixify_mode_rows as any)?.value).toBe('dimensions');
+  expect((result.matrixify_enable as any)?.value).toBe(true);
+  // Horizontal layout was NOT enabled — columns mode reset
+  expect((result.matrixify_mode_columns as any)?.value).toBe('disabled');
+});
+
+test('getControlsState preserves modes and sets matrixify_enable when old horizontal flag is true', () => {
+  const state = buildExploreState();
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_enable_horizontal_layout: true,
+    matrixify_mode_rows: 'dimensions',
+    matrixify_mode_columns: 'metrics',
+  };
+
+  const result = getControlsState(state as any, formData as any);
+  // Horizontal layout was enabled — columns mode preserved, matrixify_enable migrated
+  expect((result.matrixify_mode_columns as any)?.value).toBe('metrics');
+  expect((result.matrixify_enable as any)?.value).toBe(true);
+  // Vertical layout was NOT enabled — rows mode reset
+  expect((result.matrixify_mode_rows as any)?.value).toBe('disabled');
+});
+
+test('getControlsState preserves both modes when both old per-axis flags are true', () => {
+  const state = buildExploreState();
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_enable_vertical_layout: true,
+    matrixify_enable_horizontal_layout: true,
+    matrixify_mode_rows: 'dimensions',
+    matrixify_mode_columns: 'metrics',
+  };
+
+  const result = getControlsState(state as any, formData as any);
+  expect((result.matrixify_mode_rows as any)?.value).toBe('dimensions');
+  expect((result.matrixify_mode_columns as any)?.value).toBe('metrics');
+  expect((result.matrixify_enable as any)?.value).toBe(true);
+});
+
+test('getControlsState resets modes when old per-axis flags are explicitly false', () => {
+  const state = buildExploreState();
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_enable_vertical_layout: false,
+    matrixify_enable_horizontal_layout: false,
+    matrixify_mode_rows: 'dimensions',
+    matrixify_mode_columns: 'metrics',
+  };
+
+  const result = getControlsState(state as any, formData as any);
+  // Old flags present but false — chart never used matrixify, reset stale modes
+  expect((result.matrixify_mode_rows as any)?.value).toBe('disabled');
+  expect((result.matrixify_mode_columns as any)?.value).toBe('disabled');
+});
+
+// ============================================================
+// P2: Dashboard hydration (applyDefaultFormData) with old per-axis flags
+// ============================================================
+
+test('applyDefaultFormData preserves modes when old vertical flag is true', () => {
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_enable_vertical_layout: true,
+    matrixify_mode_rows: 'dimensions',
+    matrixify_mode_columns: 'metrics',
+  };
+
+  const outputFormData = applyDefaultFormData(formData as any);
+  expect(outputFormData.matrixify_mode_rows).toBe('dimensions');
+  expect(outputFormData.matrixify_enable).toBe(true);
+  // Horizontal not enabled — columns reset
+  expect(outputFormData.matrixify_mode_columns).toBe('disabled');
+});
+
+test('applyDefaultFormData preserves modes when both old flags are true', () => {
+  const formData = {
+    datasource: '1__table',
+    viz_type: 'test-chart',
+    matrixify_enable_vertical_layout: true,
+    matrixify_enable_horizontal_layout: true,
+    matrixify_mode_rows: 'dimensions',
+    matrixify_mode_columns: 'metrics',
+  };
+
+  const outputFormData = applyDefaultFormData(formData as any);
+  expect(outputFormData.matrixify_mode_rows).toBe('dimensions');
+  expect(outputFormData.matrixify_mode_columns).toBe('metrics');
+  expect(outputFormData.matrixify_enable).toBe(true);
+});
+
+// ============================================================
+// Direct handleDeprecatedControls tests: verify form_data mutation
+// so callers (hydrateExplore) can propagate migrated fields into state
+// ============================================================
+
+test('handleDeprecatedControls sets matrixify_enable on form_data when old vertical flag is true', () => {
+  const formData: any = {
+    matrixify_enable_vertical_layout: true,
+    matrixify_mode_rows: 'dimensions',
+    matrixify_mode_columns: 'metrics',
+  };
+  handleDeprecatedControls(formData);
+
+  expect(formData.matrixify_enable).toBe(true);
+  expect(formData.matrixify_mode_rows).toBe('dimensions');
+  // Horizontal not enabled — columns reset
+  expect(formData.matrixify_mode_columns).toBe('disabled');
+});
+
+test('handleDeprecatedControls resets modes when no matrixify_enable and no old flags', () => {
+  const formData: any = {
+    matrixify_mode_rows: 'dimensions',
+    matrixify_mode_columns: 'metrics',
+  };
+  handleDeprecatedControls(formData);
+
+  expect(formData.matrixify_enable).toBeUndefined();
+  expect(formData.matrixify_mode_rows).toBe('disabled');
+  expect(formData.matrixify_mode_columns).toBe('disabled');
+});
+
+test('handleDeprecatedControls is idempotent — no-op when matrixify_enable already present', () => {
+  const formData: any = {
+    matrixify_enable: true,
+    matrixify_mode_rows: 'dimensions',
+    matrixify_mode_columns: 'metrics',
+  };
+  handleDeprecatedControls(formData);
+
+  // No mutation — matrixify_enable key is present
+  expect(formData.matrixify_enable).toBe(true);
+  expect(formData.matrixify_mode_rows).toBe('dimensions');
+  expect(formData.matrixify_mode_columns).toBe('metrics');
+});
diff --git a/superset-frontend/src/explore/store.ts b/superset-frontend/src/explore/store.ts
index b1189efff44..79b5826df03 100644
--- a/superset-frontend/src/explore/store.ts
+++ b/superset-frontend/src/explore/store.ts
@@ -41,9 +41,16 @@ type FormData = QueryFormData & {
   y_axis_zero?: boolean;
   y_axis_bounds?: [number | null, number | null];
   datasource?: string;
+  matrixify_enable?: boolean;
+  matrixify_mode_rows?: string;
+  matrixify_mode_columns?: string;
+  // Pre-revamp per-axis enable flags (removed in #38519, may still exist in
+  // persisted form_data for charts that actually used matrixify)
+  matrixify_enable_vertical_layout?: boolean;
+  matrixify_enable_horizontal_layout?: boolean;
 };
 
-function handleDeprecatedControls(formData: FormData): void {
+export function handleDeprecatedControls(formData: FormData): void {
   // Reaffectation / handling of deprecated controls
   /* eslint-disable no-param-reassign */
 
@@ -51,6 +58,37 @@ function handleDeprecatedControls(formData: FormData): void {
   if (formData.y_axis_zero) {
     formData.y_axis_bounds = [0, null];
   }
+
+  // #38519: migrate pre-revamp matrixify controls to the new single-toggle
+  // system. Before the revamp, per-axis enable flags
+  // (matrixify_enable_vertical_layout / matrixify_enable_horizontal_layout)
+  // gated visibility, and matrixify_mode_rows/columns defaulted to
+  // non-disabled values ('dimensions'/'metrics'). The revamp replaced those
+  // with a single matrixify_enable toggle and mode default 'disabled'.
+  //
+  // Charts that actually used matrixify pre-revamp have the old per-axis
+  // flags set to true — we must preserve their modes and set
+  // matrixify_enable: true. Charts that never used matrixify (or predate it)
+  // need stale mode defaults reset to 'disabled' because 4 downstream UI
+  // consumers (ExploreChartPanel, ChartContextMenu, DrillBySubmenu,
+  // ChartRenderer) infer "matrixify is active" from mode values alone.
+  if (!('matrixify_enable' in formData)) {
+    const hadVerticalLayout =
+      formData.matrixify_enable_vertical_layout === true;
+    const hadHorizontalLayout =
+      formData.matrixify_enable_horizontal_layout === true;
+
+    if (hadVerticalLayout || hadHorizontalLayout) {
+      // Pre-revamp chart that genuinely used matrixify — migrate to new flag
+      formData.matrixify_enable = true;
+      if (!hadVerticalLayout) formData.matrixify_mode_rows = 'disabled';
+      if (!hadHorizontalLayout) formData.matrixify_mode_columns = 'disabled';
+    } else {
+      // Never used matrixify — reset stale defaults
+      formData.matrixify_mode_rows = 'disabled';
+      formData.matrixify_mode_columns = 'disabled';
+    }
+  }
 }
 
 export function getControlsState(
@@ -89,25 +127,31 @@ export function getControlsState(
 export function applyDefaultFormData(
   inputFormData: FormData,
 ): Record<string, unknown> {
-  const datasourceType = inputFormData.datasource?.split('__')[1] ?? '';
-  const vizType = inputFormData.viz_type;
+  // Normalize deprecated controls before building control state — ensures
+  // stale matrixify modes are cleaned on the dashboard hydration path too,
+  // not just the explore path (getControlsState).
+  const cleanedFormData = { ...inputFormData };
+  handleDeprecatedControls(cleanedFormData);
+
+  const datasourceType = cleanedFormData.datasource?.split('__')[1] ?? '';
+  const vizType = cleanedFormData.viz_type;
   const controlsState = getAllControlsState(
     vizType,
     datasourceType as DatasourceType,
     null,
-    inputFormData,
+    cleanedFormData,
   );
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   const controlFormData = getFormDataFromControls(controlsState as any);
 
   const formData: Record<string, unknown> = {};
   Object.keys(controlsState)
-    .concat(Object.keys(inputFormData))
+    .concat(Object.keys(cleanedFormData))
     .forEach(controlName => {
-      if (inputFormData[controlName as keyof FormData] === undefined) {
+      if (cleanedFormData[controlName as keyof FormData] === undefined) {
         formData[controlName] = controlFormData[controlName];
       } else {
-        formData[controlName] = inputFormData[controlName as keyof FormData];
+        formData[controlName] = cleanedFormData[controlName as keyof FormData];
       }
     });