diff --git a/Civi/Api4/Action/CustomGroup/Get.php b/Civi/Api4/Action/CustomGroup/Get.php
new file mode 100644
index 000000000000..5ad9da1f1193
--- /dev/null
+++ b/Civi/Api4/Action/CustomGroup/Get.php
@@ -0,0 +1,107 @@
+<?php
+
+/*
+ +--------------------------------------------------------------------+
+ | Copyright CiviCRM LLC. All rights reserved.                        |
+ |                                                                    |
+ | This work is published under the GNU AGPLv3 license with some      |
+ | permitted exceptions and without any warranty. For full license    |
+ | and copyright information, see https://civicrm.org/licensing       |
+ +--------------------------------------------------------------------+
+ */
+
+namespace Civi\Api4\Action\CustomGroup;
+
+use Civi\Api4\Generic\Result;
+use Civi\Api4\Generic\Traits\ArrayQueryActionTrait;
+use Civi\Api4\Generic\Traits\PseudoconstantOutputTrait;
+
+/**
+ * @inheritDoc
+ *
+ */
+class Get extends \Civi\Api4\Generic\DAOGetAction {
+  use ArrayQueryActionTrait;
+  use PseudoconstantOutputTrait;
+
+  /**
+   * @var bool
+   *
+   * Should we use the in-memory cache to answer
+   * this request?
+   *
+   * If unset, will be determined automatically based
+   * on the complexity of the request
+   */
+  protected ?bool $useCache = NULL;
+
+  /**
+   * @param \Civi\Api4\Generic\Result $result
+   *
+   * Use self::getFromCache or DAOGetAction::getObjects
+   */
+  protected function getObjects(Result $result): void {
+    if (is_null($this->useCache)) {
+      $this->useCache = !$this->needDatabase();
+    }
+    if ($this->useCache) {
+      $this->getFromCache($result);
+      return;
+    }
+    parent::getObjects($result);
+  }
+
+  /**
+   * Determine whether this query needs to use the
+   * database (or can be answered using the cache)
+   *
+   * @return bool
+   */
+  protected function needDatabase(): bool {
+    if ($this->groupBy || $this->having || $this->join) {
+      return TRUE;
+    }
+
+    $standardFields = \Civi::entity($this->getEntityName())->getFields();
+    foreach ($this->select as $field) {
+      [$field] = explode(':', $field);
+      if (!isset($standardFields[$field])) {
+        return TRUE;
+      }
+    }
+    foreach ($this->where as $clause) {
+      [$field] = explode(':', $clause[0] ?? '');
+      if (!$field || !isset($standardFields[$field])) {
+        return TRUE;
+      }
+      // ArrayQueryTrait doesn't yet support field-to-field comparisons
+      if (!empty($clause[3])) {
+        return TRUE;
+      }
+    }
+    foreach ($this->orderBy as $field => $dir) {
+      [$field] = explode(':', $field);
+      if (!isset($standardFields[$field])) {
+        return TRUE;
+      }
+    }
+    return FALSE;
+  }
+
+  /**
+   * This works like BasicGetAction:
+   * - provide all the records upfront from the cache
+   * - format suffixes using PseudoconstantOutputTrait
+   * - filter using ArrayQueryActionTrait
+   */
+  protected function getFromCache($result): void {
+    $values = $this->getCachedRecords();
+    $this->formatRawValues($values);
+    $this->queryArray($values, $result);
+  }
+
+  protected function getCachedRecords() {
+    return \CRM_Core_BAO_CustomGroup::getAll();
+  }
+
+}
diff --git a/Civi/Api4/CustomGroup.php b/Civi/Api4/CustomGroup.php
index 1aed113a4860..4b13fda73893 100644
--- a/Civi/Api4/CustomGroup.php
+++ b/Civi/Api4/CustomGroup.php
@@ -23,4 +23,13 @@ class CustomGroup extends Generic\DAOEntity {
   use Generic\Traits\ManagedEntity;
   use Generic\Traits\SortableEntity;
 
+  /**
+   * @param bool $checkPermissions
+   * @return Action\CustomGroup\Get
+   */
+  public static function get($checkPermissions = TRUE) {
+    return (new Action\CustomGroup\Get(__CLASS__, __FUNCTION__))
+      ->setCheckPermissions($checkPermissions);
+  }
+
 }
diff --git a/Civi/Api4/Generic/BasicGetAction.php b/Civi/Api4/Generic/BasicGetAction.php
index d8273e0dad56..24b261896d57 100644
--- a/Civi/Api4/Generic/BasicGetAction.php
+++ b/Civi/Api4/Generic/BasicGetAction.php
@@ -13,7 +13,6 @@
 namespace Civi\Api4\Generic;
 
 use Civi\API\Exception\NotImplementedException;
-use Civi\Api4\Utils\FormattingUtil;
 
 /**
  * Retrieve $ENTITIES based on criteria specified in the `where` parameter.
@@ -22,6 +21,7 @@
  */
 class BasicGetAction extends AbstractGetAction {
   use Traits\ArrayQueryActionTrait;
+  use Traits\PseudoconstantOutputTrait;
 
   /**
    * @var callable
@@ -94,30 +94,4 @@ protected function getRecords() {
     throw new NotImplementedException('Getter function not found for api4 ' . $this->getEntityName() . '::' . $this->getActionName());
   }
 
-  /**
-   * Evaluate :pseudoconstant suffix expressions and replace raw values with option values
-   *
-   * @param $records
-   * @throws \CRM_Core_Exception
-   */
-  protected function formatRawValues(&$records) {
-    // Pad $records and $fields with pseudofields
-    $fields = $this->entityFields();
-    foreach ($records as &$values) {
-      foreach ($this->entityFields() as $field) {
-        $values += [$field['name'] => $field['default_value'] ?? NULL];
-        if (!empty($field['options'])) {
-          foreach ($field['suffixes'] ?? array_keys(\CRM_Core_SelectValues::optionAttributes()) as $suffix) {
-            $pseudofield = $field['name'] . ':' . $suffix;
-            if (!isset($values[$pseudofield]) && isset($values[$field['name']]) && $this->_isFieldSelected($pseudofield)) {
-              $values[$pseudofield] = $values[$field['name']];
-            }
-          }
-        }
-      }
-      // Swap raw values with pseudoconstants
-      FormattingUtil::formatOutputValues($values, $fields, $this->getActionName());
-    }
-  }
-
 }
diff --git a/Civi/Api4/Generic/Traits/PseudoconstantOutputTrait.php b/Civi/Api4/Generic/Traits/PseudoconstantOutputTrait.php
new file mode 100644
index 000000000000..eb721ed19556
--- /dev/null
+++ b/Civi/Api4/Generic/Traits/PseudoconstantOutputTrait.php
@@ -0,0 +1,50 @@
+<?php
+
+/*
+ +--------------------------------------------------------------------+
+ | Copyright CiviCRM LLC. All rights reserved.                        |
+ |                                                                    |
+ | This work is published under the GNU AGPLv3 license with some      |
+ | permitted exceptions and without any warranty. For full license    |
+ | and copyright information, see https://civicrm.org/licensing       |
+ +--------------------------------------------------------------------+
+ */
+
+namespace Civi\Api4\Generic\Traits;
+
+use Civi\Api4\Utils\FormattingUtil;
+
+/**
+ * Helper function for formatting optionvalue/pseudoconstant fields
+ *
+ * @package Civi\Api4\Generic
+ */
+trait PseudoconstantOutputTrait {
+
+  /**
+   * Evaluate :pseudoconstant suffix expressions and replace raw values with option values
+   *
+   * @param $records
+   * @throws \CRM_Core_Exception
+   */
+  protected function formatRawValues(&$records) {
+    // Pad $records and $fields with pseudofields
+    $fields = $this->entityFields();
+    foreach ($records as &$values) {
+      foreach ($this->entityFields() as $field) {
+        $values += [$field['name'] => $field['default_value'] ?? NULL];
+        if (!empty($field['options'])) {
+          foreach ($field['suffixes'] ?? array_keys(\CRM_Core_SelectValues::optionAttributes()) as $suffix) {
+            $pseudofield = $field['name'] . ':' . $suffix;
+            if (!isset($values[$pseudofield]) && isset($values[$field['name']]) && $this->_isFieldSelected($pseudofield)) {
+              $values[$pseudofield] = $values[$field['name']];
+            }
+          }
+        }
+      }
+      // Swap raw values with pseudoconstants
+      FormattingUtil::formatOutputValues($values, $fields, $this->getActionName());
+    }
+  }
+
+}
diff --git a/tests/phpunit/api/v4/Action/CachedGetTest.php b/tests/phpunit/api/v4/Action/CachedGetTest.php
new file mode 100644
index 000000000000..3982651fc80e
--- /dev/null
+++ b/tests/phpunit/api/v4/Action/CachedGetTest.php
@@ -0,0 +1,129 @@
+<?php
+
+/*
+ +--------------------------------------------------------------------+
+ | Copyright CiviCRM LLC. All rights reserved.                        |
+ |                                                                    |
+ | This work is published under the GNU AGPLv3 license with some      |
+ | permitted exceptions and without any warranty. For full license    |
+ | and copyright information, see https://civicrm.org/licensing       |
+ +--------------------------------------------------------------------+
+ */
+
+/**
+ *
+ * @package CRM
+ * @copyright CiviCRM LLC https://civicrm.org/licensing
+ */
+
+
+namespace api\v4\Action;
+
+use api\v4\Api4TestBase;
+use Civi\Api4\CustomGroup;
+
+/**
+ * Test Api4-level caching (currently = CustomGroup)
+ *
+ *
+ * @group headless
+ */
+class CachedGetTest extends Api4TestBase {
+
+  /**
+   * @inheritdoc
+   */
+  public function setUp(): void {
+    parent::setUp();
+
+    CustomGroup::create(FALSE)
+      ->addValue('name', 'LemonPreferences')
+      ->addValue('title', 'Lemon')
+      ->addValue('extends', 'Contact')
+      ->addValue('pre_help', 'Some people think lemons are all the same, but some have preferences.')
+      ->execute();
+  }
+
+  /**
+   * @inheritDoc
+   */
+  public function tearDown(): void {
+    CustomGroup::delete(FALSE)
+      ->addWhere('name', '=', 'LemonPreferences')
+      ->execute();
+    parent::tearDown();
+  }
+
+  /**
+   * @return \Civi\Api4\Action\AbstractAction[]
+   */
+  protected function cacheableCalls(): array {
+    $calls = [];
+
+    $calls[] = CustomGroup::get(FALSE)
+      ->addWhere('name', 'CONTAINS', 'lemon');
+
+    // note: comparison should be case-insensitive
+    $calls[] = CustomGroup::get(FALSE)
+      ->addWhere('extends', '=', 'contact');
+
+    return $calls;
+  }
+
+  /**
+   * @return \Civi\Api4\Action\AbstractAction[]
+   */
+  protected function uncacheableCalls(): array {
+    $calls = [];
+
+    // cache cant GROUP BY
+    $calls[] = CustomGroup::get(FALSE)
+      ->addSelect('extends', 'COUNT(id) AS count')
+      ->addGroupBy('extends');
+
+    // cache cant do SQL functions
+    $calls[] = CustomGroup::get(FALSE)
+      ->addSelect('UPPER(name)');
+
+    // TODO: cache cant do implicit joins (but none available on CustomGroup)
+
+    return $calls;
+  }
+
+  /**
+   * For easy calls the cached result should
+   * match the database result
+   */
+  public function testCachedGetMatchesDatabase(): void {
+    foreach ($this->cacheableCalls() as $call) {
+      // we need two copies of the API action object
+      $dbCall = clone $call;
+
+      $cacheResult = (array) $call->setUseCache(TRUE)->execute();
+
+      $dbResult = (array) $dbCall->setUseCache(FALSE)->execute();
+
+      $this->assertEquals($cacheResult, $dbResult);
+    }
+  }
+
+  /**
+   * For hard calls the default result should
+   * match the database result
+   * (the API should determine it needs to escalate
+   * to a DB call if `useCache` is left unspecified)
+   */
+  public function testHardQueryUsesDatabaseByDefault(): void {
+    foreach ($this->uncacheableCalls() as $call) {
+      // we need two copies of the API action object
+      $dbCall = clone $call;
+
+      $defaultResult = (array) $call->execute();
+
+      $dbResult = (array) $dbCall->setUseCache(FALSE)->execute();
+
+      $this->assertEquals($defaultResult, $dbResult);
+    }
+  }
+
+}