diff --git a/dotcom-rendering/src/frontend/feFront.ts b/dotcom-rendering/src/frontend/feFront.ts
index e7a8eca76cf..3e576294bd0 100644
--- a/dotcom-rendering/src/frontend/feFront.ts
+++ b/dotcom-rendering/src/frontend/feFront.ts
@@ -322,6 +322,13 @@ export type FECollection = {
 };
 
 export type FEFrontConfig = {
+	/**
+	 * Server-side AB tests. Optional from `frontend`; a default of
+	 * `{}` is applied by AJV during request validation (see `useDefaults` in
+	 * `validate.ts`), so this is always present after enhancing.
+	 *
+	 * @default {}
+	 */
 	abTests: ServerSideTests;
 	adUnit: string;
 	ajaxUrl: string;
diff --git a/dotcom-rendering/src/frontend/schemas/feArticle.json b/dotcom-rendering/src/frontend/schemas/feArticle.json
index 3c7cdf9ab7d..ad6ee70f43d 100644
--- a/dotcom-rendering/src/frontend/schemas/feArticle.json
+++ b/dotcom-rendering/src/frontend/schemas/feArticle.json
@@ -5164,7 +5164,8 @@
             "type": "object",
             "properties": {
                 "abTests": {
-                    "description": "Narrowest representation of the server-side tests\nobject shape, which is [defined in `frontend`](https://github.com/guardian/frontend/blob/23743723030a041e4f4f59fa265ee2be0bb51825/common/app/experiments/ExperimentsDefinition.scala#L24-L26).\n\n**Note:** This type is not support by JSON-schema, it evaluates as `object`",
+                    "description": "Server-side AB tests. Optional from `frontend`; a default of\n`{}` is applied by AJV during request validation (see `useDefaults` in\n`validate.ts`), so this is always present after enhancing.",
+                    "default": {},
                     "type": "object"
                 },
                 "adUnit": {
diff --git a/dotcom-rendering/src/frontend/schemas/feCricketMatchPage.json b/dotcom-rendering/src/frontend/schemas/feCricketMatchPage.json
index a56ab5a3aa4..b886c7b1c70 100644
--- a/dotcom-rendering/src/frontend/schemas/feCricketMatchPage.json
+++ b/dotcom-rendering/src/frontend/schemas/feCricketMatchPage.json
@@ -573,7 +573,8 @@
                     "type": "string"
                 },
                 "abTests": {
-                    "description": "Narrowest representation of the server-side tests\nobject shape, which is [defined in `frontend`](https://github.com/guardian/frontend/blob/23743723030a041e4f4f59fa265ee2be0bb51825/common/app/experiments/ExperimentsDefinition.scala#L24-L26).\n\n**Note:** This type is not support by JSON-schema, it evaluates as `object`",
+                    "description": "Server-side AB tests. Optional from `frontend`; a default of\n`{}` is applied by AJV during request validation (see `useDefaults` in\n`validate.ts`), so this is always present after enhancing.",
+                    "default": {},
                     "type": "object"
                 },
                 "ajaxUrl": {
diff --git a/dotcom-rendering/src/frontend/schemas/feFootballMatchInfoPage.json b/dotcom-rendering/src/frontend/schemas/feFootballMatchInfoPage.json
index 3b3e7dccd76..13ea7bf0f51 100644
--- a/dotcom-rendering/src/frontend/schemas/feFootballMatchInfoPage.json
+++ b/dotcom-rendering/src/frontend/schemas/feFootballMatchInfoPage.json
@@ -480,7 +480,8 @@
                     "type": "string"
                 },
                 "abTests": {
-                    "description": "Narrowest representation of the server-side tests\nobject shape, which is [defined in `frontend`](https://github.com/guardian/frontend/blob/23743723030a041e4f4f59fa265ee2be0bb51825/common/app/experiments/ExperimentsDefinition.scala#L24-L26).\n\n**Note:** This type is not support by JSON-schema, it evaluates as `object`",
+                    "description": "Server-side AB tests. Optional from `frontend`; a default of\n`{}` is applied by AJV during request validation (see `useDefaults` in\n`validate.ts`), so this is always present after enhancing.",
+                    "default": {},
                     "type": "object"
                 },
                 "ajaxUrl": {
diff --git a/dotcom-rendering/src/frontend/schemas/feFootballMatchListPage.json b/dotcom-rendering/src/frontend/schemas/feFootballMatchListPage.json
index 359ef7e84e8..d050b811dcf 100644
--- a/dotcom-rendering/src/frontend/schemas/feFootballMatchListPage.json
+++ b/dotcom-rendering/src/frontend/schemas/feFootballMatchListPage.json
@@ -358,7 +358,8 @@
                     "type": "string"
                 },
                 "abTests": {
-                    "description": "Narrowest representation of the server-side tests\nobject shape, which is [defined in `frontend`](https://github.com/guardian/frontend/blob/23743723030a041e4f4f59fa265ee2be0bb51825/common/app/experiments/ExperimentsDefinition.scala#L24-L26).\n\n**Note:** This type is not support by JSON-schema, it evaluates as `object`",
+                    "description": "Server-side AB tests. Optional from `frontend`; a default of\n`{}` is applied by AJV during request validation (see `useDefaults` in\n`validate.ts`), so this is always present after enhancing.",
+                    "default": {},
                     "type": "object"
                 },
                 "ajaxUrl": {
diff --git a/dotcom-rendering/src/frontend/schemas/feFootballTablesPage.json b/dotcom-rendering/src/frontend/schemas/feFootballTablesPage.json
index 24a25d47027..7493767d744 100644
--- a/dotcom-rendering/src/frontend/schemas/feFootballTablesPage.json
+++ b/dotcom-rendering/src/frontend/schemas/feFootballTablesPage.json
@@ -351,7 +351,8 @@
                     "type": "string"
                 },
                 "abTests": {
-                    "description": "Narrowest representation of the server-side tests\nobject shape, which is [defined in `frontend`](https://github.com/guardian/frontend/blob/23743723030a041e4f4f59fa265ee2be0bb51825/common/app/experiments/ExperimentsDefinition.scala#L24-L26).\n\n**Note:** This type is not support by JSON-schema, it evaluates as `object`",
+                    "description": "Server-side AB tests. Optional from `frontend`; a default of\n`{}` is applied by AJV during request validation (see `useDefaults` in\n`validate.ts`), so this is always present after enhancing.",
+                    "default": {},
                     "type": "object"
                 },
                 "ajaxUrl": {
diff --git a/dotcom-rendering/src/frontend/schemas/feFront.json b/dotcom-rendering/src/frontend/schemas/feFront.json
index dfd5240e9e6..676aa1a8ebd 100644
--- a/dotcom-rendering/src/frontend/schemas/feFront.json
+++ b/dotcom-rendering/src/frontend/schemas/feFront.json
@@ -3479,7 +3479,8 @@
                     "type": "object",
                     "properties": {
                         "abTests": {
-                            "description": "Narrowest representation of the server-side tests\nobject shape, which is [defined in `frontend`](https://github.com/guardian/frontend/blob/23743723030a041e4f4f59fa265ee2be0bb51825/common/app/experiments/ExperimentsDefinition.scala#L24-L26).\n\n**Note:** This type is not support by JSON-schema, it evaluates as `object`",
+                            "description": "Server-side AB tests. Optional from `frontend`; a default of\n`{}` is applied by AJV during request validation (see `useDefaults` in\n`validate.ts`), so this is always present after enhancing.",
+                            "default": {},
                             "type": "object"
                         },
                         "adUnit": {
diff --git a/dotcom-rendering/src/frontend/schemas/feTagPage.json b/dotcom-rendering/src/frontend/schemas/feTagPage.json
index 066ed439a43..67cf9a5b7bc 100644
--- a/dotcom-rendering/src/frontend/schemas/feTagPage.json
+++ b/dotcom-rendering/src/frontend/schemas/feTagPage.json
@@ -1639,7 +1639,8 @@
                     "type": "object",
                     "properties": {
                         "abTests": {
-                            "description": "Narrowest representation of the server-side tests\nobject shape, which is [defined in `frontend`](https://github.com/guardian/frontend/blob/23743723030a041e4f4f59fa265ee2be0bb51825/common/app/experiments/ExperimentsDefinition.scala#L24-L26).\n\n**Note:** This type is not support by JSON-schema, it evaluates as `object`",
+                            "description": "Server-side AB tests. Optional from `frontend`; a default of\n`{}` is applied by AJV during request validation (see `useDefaults` in\n`validate.ts`), so this is always present after enhancing.",
+                            "default": {},
                             "type": "object"
                         },
                         "adUnit": {
diff --git a/dotcom-rendering/src/model/newsletter-page-schema.json b/dotcom-rendering/src/model/newsletter-page-schema.json
index 100a26025ad..9f87ec4ef83 100644
--- a/dotcom-rendering/src/model/newsletter-page-schema.json
+++ b/dotcom-rendering/src/model/newsletter-page-schema.json
@@ -130,7 +130,8 @@
                     "$ref": "#/definitions/Switches"
                 },
                 "abTests": {
-                    "description": "Narrowest representation of the server-side tests\nobject shape, which is [defined in `frontend`](https://github.com/guardian/frontend/blob/23743723030a041e4f4f59fa265ee2be0bb51825/common/app/experiments/ExperimentsDefinition.scala#L24-L26).\n\n**Note:** This type is not support by JSON-schema, it evaluates as `object`",
+                    "description": "Server-side AB tests. Optional from `frontend`; a default of\n`{}` is applied by AJV during request validation (see `useDefaults` in\n`validate.ts`), so this is always present after enhancing.",
+                    "default": {},
                     "type": "object"
                 },
                 "serverSideABTests": {
diff --git a/dotcom-rendering/src/types/config.ts b/dotcom-rendering/src/types/config.ts
index 65f711a8d4c..e89cfa30622 100644
--- a/dotcom-rendering/src/types/config.ts
+++ b/dotcom-rendering/src/types/config.ts
@@ -44,6 +44,13 @@ export interface Switches {
  * this data could eventually be defined in dotcom-rendering
  */
 export interface ConfigType extends CommercialConfigType, LegacyConfig {
+	/**
+	 * Server-side AB tests. Optional from `frontend`; a default of
+	 * `{}` is applied by AJV during request validation (see `useDefaults` in
+	 * `validate.ts`), so this is always present after enhancing.
+	 *
+	 * @default {}
+	 */
 	abTests: ServerSideTests;
 	adUnit: string;
 	ajaxUrl: string;
diff --git a/dotcom-rendering/src/types/newslettersPage.ts b/dotcom-rendering/src/types/newslettersPage.ts
index b2220d43022..12791ea9ec7 100644
--- a/dotcom-rendering/src/types/newslettersPage.ts
+++ b/dotcom-rendering/src/types/newslettersPage.ts
@@ -14,6 +14,13 @@ type FENewslettersConfigType = {
 	sentryHost: string;
 	dcrSentryDsn: string; // used in dotcom-rendering/src/client/sentryLoader/sentry.ts
 	switches: Switches;
+	/**
+	 * Server-side AB tests. Optional from `frontend`; a default of
+	 * `{}` is applied by AJV during request validation (see `useDefaults` in
+	 * `validate.ts`), so this is always present after enhancing.
+	 *
+	 * @default {}
+	 */
 	abTests: ServerSideTests;
 	serverSideABTests: Record<string, string>;
 	dfpAccountId: string;