diff --git a/core/modules/block/src/Plugin/ConfigAction/PlaceBlock.php b/core/modules/block/src/Plugin/ConfigAction/PlaceBlock.php
new file mode 100644
index 0000000000000000000000000000000000000000..19f51ca082782ec82abc424edec3602722db20b1
--- /dev/null
+++ b/core/modules/block/src/Plugin/ConfigAction/PlaceBlock.php
@@ -0,0 +1,95 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block\Plugin\ConfigAction;
+
+use Drupal\block\BlockInterface;
+use Drupal\Core\Config\Action\Attribute\ConfigAction;
+use Drupal\Core\Config\Action\ConfigActionException;
+use Drupal\Core\Config\Action\ConfigActionPluginInterface;
+use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\Config\Entity\ConfigEntityStorageInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Places a block in either the admin or default theme.
+ *
+ * @internal
+ * This API is experimental.
+ */
+#[ConfigAction(
+ id: 'placeBlock',
+ admin_label: new TranslatableMarkup('Place a block'),
+ entity_types: ['block'],
+ deriver: PlaceBlockDeriver::class,
+)]
+final class PlaceBlock implements ConfigActionPluginInterface, ContainerFactoryPluginInterface {
+
+ public function __construct(
+ private readonly ConfigActionPluginInterface $createAction,
+ private readonly string $whichTheme,
+ private readonly ConfigFactoryInterface $configFactory,
+ private readonly ConfigEntityStorageInterface $blockStorage,
+ ) {}
+
+ /**
+ * {@inheritdoc}
+ */
+ public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+ return new static(
+ $container->get('plugin.manager.config_action')->createInstance('entity_create:createIfNotExists'),
+ $plugin_definition['which_theme'],
+ $container->get(ConfigFactoryInterface::class),
+ $container->get(EntityTypeManagerInterface::class)->getStorage('block'),
+ );
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function apply(string $configName, mixed $value): void {
+ assert(is_array($value));
+
+ $theme = $this->configFactory->get('system.theme')->get($this->whichTheme);
+ $value['theme'] = $theme;
+
+ if (array_key_exists('region', $value)) {
+ // Since the recipe author might not know ahead of time what theme the
+ // block is in, they should supply a map whose keys are theme names and
+ // values are region names, so we know where to place this block. If the
+ // target theme is not in the map, they should supply the name of a
+ // fallback region. If all that fails, give up with an exception.
+ assert(is_array($value['region']));
+ $value['region'] = $value['region'][$theme] ?? $value['default_region'] ?? throw new ConfigActionException("Cannot determine which region to place this block into, because no default region was provided.");
+ }
+
+ // Allow the recipe author to position the block in the region without
+ // needing to know exact weights.
+ if (array_key_exists('position', $value)) {
+ $blocks = $this->blockStorage->loadByProperties([
+ 'theme' => $theme,
+ 'region' => $value['region'],
+ ]);
+ // Sort the blocks by weight. Don't use \Drupal\block\Entity\Block::sort()
+ // here because it seems to be intended to sort blocks in the UI, where
+ // we really just want to get the weights right in this situation.
+ uasort($blocks, fn (BlockInterface $a, BlockInterface $b) => $a->getWeight() <=> $b->getWeight());
+
+ $value['weight'] = match ($value['position']) {
+ 'first' => reset($blocks)->getWeight() - 1,
+ 'last' => end($blocks)->getWeight() + 1,
+ };
+ }
+ // Remove values that are not valid properties of block entities.
+ unset($value['position'], $value['default_region']);
+ // Ensure a weight is set by default.
+ $value += ['weight' => 0];
+
+ $this->createAction->apply($configName, $value);
+ }
+
+}
diff --git a/core/modules/block/src/Plugin/ConfigAction/PlaceBlockDeriver.php b/core/modules/block/src/Plugin/ConfigAction/PlaceBlockDeriver.php
new file mode 100644
index 0000000000000000000000000000000000000000..7c7ebbcdb8b0d423985a5bfd113a3aa005db5f6f
--- /dev/null
+++ b/core/modules/block/src/Plugin/ConfigAction/PlaceBlockDeriver.php
@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block\Plugin\ConfigAction;
+
+use Drupal\Component\Plugin\Derivative\DeriverBase;
+
+/**
+ * Defines a deriver for the `placeBlock` config action.
+ *
+ * This creates two actions: `placeBlockInDefaultTheme`, and
+ * `placeBlockInAdminTheme`. They behave identically except for which theme
+ * they target.
+ */
+final class PlaceBlockDeriver extends DeriverBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public function getDerivativeDefinitions($base_plugin_definition) {
+ $this->derivatives['placeBlockInAdminTheme'] = [
+ 'which_theme' => 'admin',
+ ] + $base_plugin_definition;
+ $this->derivatives['placeBlockInDefaultTheme'] = [
+ 'which_theme' => 'default',
+ ] + $base_plugin_definition;
+
+ return parent::getDerivativeDefinitions($base_plugin_definition);
+ }
+
+}
diff --git a/core/modules/block/tests/src/Kernel/ConfigActionsTest.php b/core/modules/block/tests/src/Kernel/ConfigActionsTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..e4078943f9b5d782128c8d3516af8afbb9a8bc59
--- /dev/null
+++ b/core/modules/block/tests/src/Kernel/ConfigActionsTest.php
@@ -0,0 +1,143 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel;
+
+use Drupal\block\Entity\Block;
+use Drupal\Component\Plugin\Exception\PluginNotFoundException;
+use Drupal\Core\Config\Action\ConfigActionException;
+use Drupal\Core\Config\Action\ConfigActionManager;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Extension\ThemeInstallerInterface;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * @covers \Drupal\block\Plugin\ConfigAction\PlaceBlock
+ * @covers \Drupal\block\Plugin\ConfigAction\PlaceBlockDeriver
+ * @group block
+ */
+class ConfigActionsTest extends KernelTestBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ protected static $modules = ['block', 'user', 'system'];
+
+ private readonly ConfigActionManager $configActionManager;
+
+ /**
+ * {@inheritdoc}
+ */
+ protected function setUp(): void {
+ parent::setUp();
+ $this->container->get(ThemeInstallerInterface::class)->install([
+ 'olivero',
+ 'claro',
+ 'umami',
+ ]);
+ $this->config('system.theme')
+ ->set('default', 'olivero')
+ ->set('admin', 'claro')
+ ->save();
+
+ $this->configActionManager = $this->container->get('plugin.manager.config_action');
+ }
+
+ /**
+ * @testWith ["placeBlockInDefaultTheme"]
+ * ["placeBlockInAdminTheme"]
+ */
+ public function testActionOnlyWorksOnBlocks(string $action): void {
+ $this->expectException(PluginNotFoundException::class);
+ $this->expectExceptionMessage("The \"$action\" plugin does not exist.");
+ $this->configActionManager->applyAction($action, 'user.role.anonymous', []);
+ }
+
+ public function testExistingBlockIsNotChanged(): void {
+ $extant_region = Block::load('olivero_powered')->getRegion();
+ $this->assertNotSame('content', $extant_region);
+
+ $this->configActionManager->applyAction('placeBlockInDefaultTheme', 'block.block.olivero_powered', [
+ 'plugin' => 'system_powered_by_block',
+ 'region' => [
+ 'olivero' => 'content',
+ ],
+ ]);
+ // The extant block should be unchanged.
+ $this->assertSame($extant_region, Block::load('olivero_powered')->getRegion());
+ }
+
+ /**
+ * @testWith ["placeBlockInDefaultTheme", "olivero", "header"]
+ * ["placeBlockInAdminTheme", "claro", "page_bottom"]
+ */
+ public function testPlaceBlockInTheme(string $action, string $expected_theme, string $expected_region): void {
+ $this->configActionManager->applyAction($action, 'block.block.test_block', [
+ 'plugin' => 'system_powered_by_block',
+ 'region' => [
+ 'olivero' => 'header',
+ 'claro' => 'page_bottom',
+ ],
+ 'default_region' => 'content',
+ ]);
+
+ $block = Block::load('test_block');
+ $this->assertInstanceOf(Block::class, $block);
+ $this->assertSame('system_powered_by_block', $block->getPluginId());
+ $this->assertSame($expected_theme, $block->getTheme());
+ $this->assertSame($expected_region, $block->getRegion());
+
+ $this->expectException(ConfigActionException::class);
+ $this->expectExceptionMessage('Cannot determine which region to place this block into, because no default region was provided.');
+ $this->configActionManager->applyAction($action, 'block.block.no_region', [
+ 'plugin' => 'system_powered_by_block',
+ 'region' => [],
+ ]);
+ }
+
+ public function testPlaceBlockInDefaultRegion(): void {
+ $this->config('system.theme')->set('default', 'umami')->save();
+ $this->testPlaceBlockInTheme('placeBlockInDefaultTheme', 'umami', 'content');
+ }
+
+ public function testPlaceBlockAtPosition(): void {
+ // Ensure there's at least one block already in the region.
+ $block = Block::create([
+ 'id' => 'block_1',
+ 'theme' => 'olivero',
+ 'region' => 'content_above',
+ 'weight' => 0,
+ 'plugin' => 'system_powered_by_block',
+ ]);
+ $block->save();
+
+ $this->configActionManager->applyAction('placeBlockInDefaultTheme', 'block.block.first', [
+ 'plugin' => $block->getPluginId(),
+ 'region' => [
+ $block->getTheme() => $block->getRegion(),
+ ],
+ 'position' => 'first',
+ ]);
+ $this->configActionManager->applyAction('placeBlockInDefaultTheme', 'block.block.last', [
+ 'plugin' => $block->getPluginId(),
+ 'region' => [
+ $block->getTheme() => $block->getRegion(),
+ ],
+ 'position' => 'last',
+ ]);
+
+ // Query for blocks in the region, ordered by weight.
+ $blocks = $this->container->get(EntityTypeManagerInterface::class)
+ ->getStorage('block')
+ ->getQuery()
+ ->condition('theme', $block->getTheme())
+ ->condition('region', $block->getRegion())
+ ->sort('weight', 'ASC')
+ ->execute();
+ $this->assertGreaterThanOrEqual(3, $blocks);
+ $this->assertSame('first', key($blocks));
+ $this->assertSame('last', end($blocks));
+ }
+
+}