diff --git a/.github/actions/yarn/action.yml b/.github/actions/yarn/action.yml
index 2aa211a518..814291b09d 100644
--- a/.github/actions/yarn/action.yml
+++ b/.github/actions/yarn/action.yml
@@ -1,6 +1,12 @@
 name: 'Setup Node & yarn'
 description: 'Setup a NodeJS environment, install deps, & builds packages'
 
+inputs:
+  immutable:
+    description: 'Run yarn install with --immutable (fail if lockfile would change)'
+    required: false
+    default: 'true'
+
 runs:
   using: 'composite'
   steps:
@@ -13,4 +19,9 @@ runs:
       shell: bash
     - name: Install dependencies
       shell: bash
-      run: yarn install --immutable
+      run: |
+        if [ "${{ inputs.immutable }}" = "true" ]; then
+          yarn install --immutable
+        else
+          yarn install
+        fi
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 3322ad9daf..a2362993f0 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -20,13 +20,30 @@ permissions:
 
 jobs:
   test:
+    name: Test (React ${{ matrix.react_version }})
     runs-on: ubuntu-24.04
     timeout-minutes: 30
+    strategy:
+      matrix:
+        react_version: [18, 19]
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
           fetch-depth: 0
+      - name: Set React version
+        if: matrix.react_version == 18
+        run: |
+          node -e "
+          const p = require('./package.json');
+          p.resolutions['react'] = '18.3.1';
+          p.resolutions['react-dom'] = '18.3.1';
+          p.resolutions['@types/react'] = '18.3.1';
+          p.resolutions['@types/react-dom'] = '18.3.0';
+          require('fs').writeFileSync('package.json', JSON.stringify(p, null, 2));
+          "
       - uses: ./.github/actions/yarn
+        with:
+          immutable: ${{ matrix.react_version == 19 }}
       - name: Fetch main branch
         run: git fetch origin main:main
         if: github.event_name == 'pull_request'
diff --git a/package.json b/package.json
index 5579ff15cd..9bf1d8bfd3 100644
--- a/package.json
+++ b/package.json
@@ -52,8 +52,8 @@
     "@types/invariant": "2.2.29",
     "@types/konami-code-js": "^0.8.0",
     "@types/lodash": "4.17.23",
-    "@types/react": "^18.2.0",
-    "@types/react-dom": "^18.2.0",
+    "@types/react": "^19.0.0",
+    "@types/react-dom": "^19.0.0",
     "@types/react-test-renderer": "^19.1.0",
     "@types/stylis": "^4.2.0",
     "@typescript-eslint/eslint-plugin": "^5.15.0",
@@ -113,10 +113,10 @@
   "repository": "git@github.com:Codecademy/gamut.git",
   "resolutions": {
     "@typescript-eslint/utils": "^5.15.0",
-    "@types/react": "18.3.1",
-    "@types/react-dom": "18.3.0",
-    "react": "18.3.1",
-    "react-dom": "18.3.1",
+    "@types/react": "^19.0.0",
+    "@types/react-dom": "^19.0.0",
+    "react": "^19.0.0",
+    "react-dom": "^19.0.0",
     "error-ex": "1.3.4"
   },
   "scripts": {
diff --git a/packages/gamut-icons/package.json b/packages/gamut-icons/package.json
index 28f3f47dad..fe7087b347 100644
--- a/packages/gamut-icons/package.json
+++ b/packages/gamut-icons/package.json
@@ -18,7 +18,7 @@
     "@emotion/styled": "^11.3.0",
     "@types/react": "^18.0.0 || ^19.0.0",
     "lodash": "^4.17.5",
-    "react": "^17.0.2 || ^18.2.0 || ^19.0.0"
+    "react": "^18.2.0 || ^19.0.0"
   },
   "publishConfig": {
     "access": "public"
diff --git a/packages/gamut-illustrations/package.json b/packages/gamut-illustrations/package.json
index d6a98ea6d7..492fc5d830 100644
--- a/packages/gamut-illustrations/package.json
+++ b/packages/gamut-illustrations/package.json
@@ -19,8 +19,8 @@
     "@emotion/react": "^11.4.0",
     "@emotion/styled": "^11.3.0",
     "@types/react": "^18.0.0 || ^19.0.0",
-    "react": "^17.0.2 || ^18.2.0 || ^19.0.0",
-    "react-dom": "^17.0.2 || ^18.2.0 || ^19.0.0"
+    "react": "^18.2.0 || ^19.0.0",
+    "react-dom": "^18.2.0 || ^19.0.0"
   },
   "publishConfig": {
     "access": "public"
diff --git a/packages/gamut-patterns/package.json b/packages/gamut-patterns/package.json
index 845a7356b5..579973866e 100644
--- a/packages/gamut-patterns/package.json
+++ b/packages/gamut-patterns/package.json
@@ -20,8 +20,8 @@
     "@emotion/react": "^11.4.0",
     "@emotion/styled": "^11.3.0",
     "@types/react": "^18.0.0 || ^19.0.0",
-    "react": "^17.0.2 || ^18.2.0 || ^19.0.0",
-    "react-dom": "^17.0.2 || ^18.2.0 || ^19.0.0"
+    "react": "^18.2.0 || ^19.0.0",
+    "react-dom": "^18.2.0 || ^19.0.0"
   },
   "publishConfig": {
     "access": "public"
diff --git a/packages/gamut-styles/package.json b/packages/gamut-styles/package.json
index 8deacc9bb8..1f16ee8cfc 100644
--- a/packages/gamut-styles/package.json
+++ b/packages/gamut-styles/package.json
@@ -25,7 +25,7 @@
     "@emotion/styled": "^11.3.0",
     "@types/react": "^18.0.0 || ^19.0.0",
     "lodash": "^4.17.5",
-    "react": "^17.0.2 || ^18.2.0 || ^19.0.0",
+    "react": "^18.2.0 || ^19.0.0",
     "stylis": "^4.0.7"
   },
   "publishConfig": {
diff --git a/packages/gamut-tests/package.json b/packages/gamut-tests/package.json
index 4177bd02f7..c8bd24d90e 100644
--- a/packages/gamut-tests/package.json
+++ b/packages/gamut-tests/package.json
@@ -23,7 +23,7 @@
   "module": "dist/index.js",
   "peerDependencies": {
     "@types/react": "^18.0.0 || ^19.0.0",
-    "react": "^17.0.2 || ^18.2.0 || ^19.0.0"
+    "react": "^18.2.0 || ^19.0.0"
   },
   "publishConfig": {
     "access": "public"
diff --git a/packages/gamut/package.json b/packages/gamut/package.json
index 62fa61feda..64c5623012 100644
--- a/packages/gamut/package.json
+++ b/packages/gamut/package.json
@@ -38,8 +38,8 @@
     "@emotion/react": "^11.4.0",
     "@emotion/styled": "^11.3.0",
     "@types/react": "^18.0.0 || ^19.0.0",
-    "react": "^17.0.2 || ^18.2.0 || ^19.0.0",
-    "react-dom": "^17.0.2 || ^18.2.0 || ^19.0.0"
+    "react": "^18.2.0 || ^19.0.0",
+    "react-dom": "^18.2.0 || ^19.0.0"
   },
   "publishConfig": {
     "access": "public"