diff --git a/.circleci/config.yml b/.circleci/config.yml
index 894e52fab609d..7ce9c199d4c7f 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -281,7 +281,7 @@ jobs:
           at: .
       - setup_node_modules
       - run: ./scripts/circleci/download_devtools_regression_build.js << parameters.version >> --replaceBuild
-      - run: node ./scripts/jest/jest-cli.js --build --project devtools --release-channel=experimental --reactVersion << parameters.version >> --ci
+      - run: node ./scripts/jest/jest-cli.js --build --project devtools --release-channel=experimental --reactVersion << parameters.version >> --ci=circleci
 
   run_devtools_e2e_tests_for_versions:
     docker: *docker
@@ -368,7 +368,7 @@ jobs:
     steps:
       - checkout
       - setup_node_modules
-      - run: yarn test <<parameters.args>> --ci
+      - run: yarn test <<parameters.args>> --ci=circleci
 
   yarn_test_build:
     docker: *docker
@@ -382,7 +382,7 @@ jobs:
       - attach_workspace:
           at: .
       - setup_node_modules
-      - run: yarn test --build <<parameters.args>> --ci
+      - run: yarn test --build <<parameters.args>> --ci=circleci
 
   RELEASE_CHANNEL_stable_yarn_test_dom_fixtures:
     docker: *docker
diff --git a/.github/workflows/fuzz_tests.yml b/.github/workflows/fuzz_tests.yml
index 492dd7dc4c81d..4c4373be373ea 100644
--- a/.github/workflows/fuzz_tests.yml
+++ b/.github/workflows/fuzz_tests.yml
@@ -28,5 +28,5 @@ jobs:
       shell: bash
     - name: Run fuzz tests
       run: |-
-        FUZZ_TEST_SEED=$RANDOM yarn test fuzz --ci
-        FUZZ_TEST_SEED=$RANDOM yarn test --prod fuzz --ci
+        FUZZ_TEST_SEED=$RANDOM yarn test fuzz --ci=github
+        FUZZ_TEST_SEED=$RANDOM yarn test --prod fuzz --ci=github
diff --git a/.github/workflows/runtime_test.yml b/.github/workflows/runtime_test.yml
index 1acce045217ee..a9ec4dbc7acd1 100644
--- a/.github/workflows/runtime_test.yml
+++ b/.github/workflows/runtime_test.yml
@@ -7,37 +7,67 @@ on:
     paths-ignore:
       - 'compiler/**'
 
+env:
+  # Number of workers (one per shard) to spawn
+  SHARD_COUNT: 5
+
 jobs:
+  # Define the various test parameters and parallelism for this workflow
+  build_test_params:
+    name: Build test params
+    runs-on: ubuntu-latest
+    outputs:
+      params: ${{ steps.define-params.outputs.result }}
+      shard_id: ${{ steps.define-shards.outputs.result }}
+    steps:
+      - uses: actions/github-script@v7
+        id: define-shards
+        with:
+          script: |
+            function range(from, to) {
+              const arr = [];
+              for (let n = from; n <= to; n++) {
+                arr.push(n);
+              }
+              return arr;
+            }
+            return range(1, process.env.SHARD_COUNT);
+      - uses: actions/github-script@v7
+        id: define-params
+        with:
+          script: |
+            return [
+              "-r=stable --env=development",
+              "-r=stable --env=production",
+              "-r=experimental --env=development",
+              "-r=experimental --env=production",
+              "-r=www-classic --env=development --variant=false",
+              "-r=www-classic --env=production --variant=false",
+              "-r=www-classic --env=development --variant=true",
+              "-r=www-classic --env=production --variant=true",
+              "-r=www-modern --env=development --variant=false",
+              "-r=www-modern --env=production --variant=false",
+              "-r=www-modern --env=development --variant=true",
+              "-r=www-modern --env=production --variant=true",
+              "-r=xplat --env=development --variant=false",
+              "-r=xplat --env=development --variant=true",
+              "-r=xplat --env=production --variant=false",
+              "-r=xplat --env=production --variant=true",
+              // TODO: Test more persistent configurations?
+              "-r=stable --env=development --persistent",
+              "-r=experimental --env=development --persistent"
+            ];
+
+  # Spawn a job for each shard for a given set of test params
   test:
-    name: yarn test
+    name: yarn test ${{ matrix.params }} (Shard ${{ matrix.shard_id }})
     runs-on: ubuntu-latest
-    continue-on-error: true
+    needs: build_test_params
     strategy:
       matrix:
-        # Intentionally passing these as strings instead of creating a
-        # separate parameter per CLI argument, since it's easier to
-        # control/see which combinations we want to run.
-        params: [
-          "-r=stable --env=development",
-          "-r=stable --env=production",
-          "-r=experimental --env=development",
-          "-r=experimental --env=production",
-          "-r=www-classic --env=development --variant=false",
-          "-r=www-classic --env=production --variant=false",
-          "-r=www-classic --env=development --variant=true",
-          "-r=www-classic --env=production --variant=true",
-          "-r=www-modern --env=development --variant=false",
-          "-r=www-modern --env=production --variant=false",
-          "-r=www-modern --env=development --variant=true",
-          "-r=www-modern --env=production --variant=true",
-          "-r=xplat --env=development --variant=false",
-          "-r=xplat --env=development --variant=true",
-          "-r=xplat --env=production --variant=false",
-          "-r=xplat --env=production --variant=true",
-          # TODO: Test more persistent configurations?
-          "-r=stable --env=development --persistent",
-          "-r=experimental --env=development --persistent"
-        ]
+        params: ${{ fromJSON(needs.build_test_params.outputs.params) }}
+        shard_id: ${{ fromJSON(needs.build_test_params.outputs.shard_id) }}
+    continue-on-error: true
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
@@ -52,4 +82,4 @@ jobs:
           path: "**/node_modules"
           key: ${{ runner.arch }}-${{ runner.os }}-modules-${{ hashFiles('yarn.lock') }}
       - run: yarn install --frozen-lockfile
-      - run: yarn test ${{ matrix.params }} --ci
+      - run: yarn test ${{ matrix.params }} --ci=github --shard=${{ matrix.shard_id }}/${{ env.SHARD_COUNT }}
diff --git a/packages/react-dom/src/__tests__/ReactMultiChildText-test.js b/packages/react-dom/src/__tests__/ReactMultiChildText-test.js
index c32d13d3b0151..5aeb321308090 100644
--- a/packages/react-dom/src/__tests__/ReactMultiChildText-test.js
+++ b/packages/react-dom/src/__tests__/ReactMultiChildText-test.js
@@ -77,7 +77,7 @@ const expectChildren = function (container, children) {
  * faster to render and update.
  */
 describe('ReactMultiChildText', () => {
-  jest.setTimeout(20000);
+  jest.setTimeout(30000);
 
   it('should correctly handle all possible children for render and update', async () => {
     await expect(async () => {
diff --git a/scripts/jest/jest-cli.js b/scripts/jest/jest-cli.js
index 9c3be220fb645..70d4d04b2b456 100644
--- a/scripts/jest/jest-cli.js
+++ b/scripts/jest/jest-cli.js
@@ -91,8 +91,8 @@ const argv = yargs
     ci: {
       describe: 'Run tests in CI',
       requiresArg: false,
-      type: 'boolean',
-      default: false,
+      type: 'choices',
+      choices: ['circleci', 'github'],
     },
     compactConsole: {
       alias: 'c',
@@ -309,10 +309,14 @@ function getCommandArgs() {
   }
 
   // CI Environments have limited workers.
-  if (argv.ci) {
+  if (argv.ci === 'circleci') {
     args.push('--maxWorkers=2');
   }
 
+  if (argv.ci === 'github') {
+    args.push('--maxConcurrency=10');
+  }
+
   // Push the remaining args onto the command.
   // This will send args like `--watch` to Jest.
   args.push(...argv._);
@@ -364,16 +368,18 @@ function main() {
   const envars = getEnvars();
   const env = Object.entries(envars).map(([k, v]) => `${k}=${v}`);
 
-  // Print the full command we're actually running.
-  const command = `$ ${env.join(' ')} node ${args.join(' ')}`;
-  console.log(chalk.dim(command));
+  if (argv.ci !== 'github') {
+    // Print the full command we're actually running.
+    const command = `$ ${env.join(' ')} node ${args.join(' ')}`;
+    console.log(chalk.dim(command));
 
-  // Print the release channel and project we're running for quick confirmation.
-  console.log(
-    chalk.blue(
-      `\nRunning tests for ${argv.project} (${argv.releaseChannel})...`
-    )
-  );
+    // Print the release channel and project we're running for quick confirmation.
+    console.log(
+      chalk.blue(
+        `\nRunning tests for ${argv.project} (${argv.releaseChannel})...`
+      )
+    );
+  }
 
   // Print a message that the debugger is starting just
   // for some extra feedback when running the debugger.