diff --git a/.changeset/simplify-extension-attach-to.md b/.changeset/simplify-extension-attach-to.md
new file mode 100644
index 0000000000..2beb00d056
--- /dev/null
+++ b/.changeset/simplify-extension-attach-to.md
@@ -0,0 +1,5 @@
+---
+'@backstage/frontend-plugin-api': minor
+---
+
+**BREAKING**: Simplified the `ExtensionAttachTo` type to only support a single attachment target. The array form for attaching to multiple extension points has been removed. Also removed the deprecated `ExtensionAttachToSpec` type alias.
diff --git a/packages/core-compat-api/src/collectEntityPageContents.test.tsx b/packages/core-compat-api/src/collectEntityPageContents.test.tsx
index fd74a7e89b..5ee1439360 100644
--- a/packages/core-compat-api/src/collectEntityPageContents.test.tsx
+++ b/packages/core-compat-api/src/collectEntityPageContents.test.tsx
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import { ExtensionAttachToSpec } from '@backstage/frontend-plugin-api';
+import { ExtensionAttachTo } from '@backstage/frontend-plugin-api';
 import { EntityLayout, EntitySwitch, isKind } from '@backstage/plugin-catalog';
 import { JSX } from 'react';
 import { collectEntityPageContents } from './collectEntityPageContents';
@@ -73,7 +73,7 @@ const otherTestContent = (
 function collect(element: JSX.Element) {
   const result = new Array<{
     id: string;
-    attachTo: ExtensionAttachToSpec;
+    attachTo: ExtensionAttachTo;
   }>();
 
   collectEntityPageContents(element, {
diff --git a/packages/frontend-app-api/src/tree/resolveAppTree.test.ts b/packages/frontend-app-api/src/tree/resolveAppTree.test.ts
index bffc156509..a8e63f82e0 100644
--- a/packages/frontend-app-api/src/tree/resolveAppTree.test.ts
+++ b/packages/frontend-app-api/src/tree/resolveAppTree.test.ts
@@ -149,7 +149,7 @@ describe('buildAppTree', () => {
           attachTo: [
             { id: 'a', input: 'x' },
             { id: 'b', input: 'x' },
-          ],
+          ] as any,
         },
         {
           ...baseSpec,
@@ -157,7 +157,7 @@ describe('buildAppTree', () => {
           attachTo: [
             { id: 'b', input: 'x' },
             { id: 'c', input: 'x' },
-          ],
+          ] as any,
         },
       ],
       collector,
diff --git a/packages/frontend-plugin-api/report.api.md b/packages/frontend-plugin-api/report.api.md
index c38f158b25..15450efbdd 100644
--- a/packages/frontend-plugin-api/report.api.md
+++ b/packages/frontend-plugin-api/report.api.md
@@ -921,7 +921,7 @@ export interface Extension<TConfig, TConfigInput = TConfig> {
   // (undocumented)
   $$type: '@backstage/Extension';
   // (undocumented)
-  readonly attachTo: ExtensionAttachToSpec;
+  readonly attachTo: ExtensionAttachTo;
   // (undocumented)
   readonly configSchema?: PortableSchema<TConfig, TConfigInput>;
   // (undocumented)
@@ -931,18 +931,10 @@ export interface Extension<TConfig, TConfigInput = TConfig> {
 }
 
 // @public (undocumented)
-export type ExtensionAttachTo =
-  | {
-      id: string;
-      input: string;
-    }
-  | Array<{
-      id: string;
-      input: string;
-    }>;
-
-// @public @deprecated (undocumented)
-export type ExtensionAttachToSpec = ExtensionAttachTo;
+export type ExtensionAttachTo = {
+  id: string;
+  input: string;
+};
 
 // @public (undocumented)
 export interface ExtensionBlueprint<
diff --git a/packages/frontend-plugin-api/src/wiring/index.ts b/packages/frontend-plugin-api/src/wiring/index.ts
index 3ca0be2757..044bf03b67 100644
--- a/packages/frontend-plugin-api/src/wiring/index.ts
+++ b/packages/frontend-plugin-api/src/wiring/index.ts
@@ -57,7 +57,6 @@ export {
 export {
   type Extension,
   type ExtensionAttachTo,
-  type ExtensionAttachToSpec,
 } from './resolveExtensionDefinition';
 export {
   type ExtensionDataContainer,
diff --git a/packages/frontend-plugin-api/src/wiring/resolveExtensionDefinition.ts b/packages/frontend-plugin-api/src/wiring/resolveExtensionDefinition.ts
index 605e75bfe8..70a0bd7837 100644
--- a/packages/frontend-plugin-api/src/wiring/resolveExtensionDefinition.ts
+++ b/packages/frontend-plugin-api/src/wiring/resolveExtensionDefinition.ts
@@ -30,21 +30,13 @@ import {
 } from '@internal/frontend';
 
 /** @public */
-export type ExtensionAttachTo =
-  | { id: string; input: string }
-  | Array<{ id: string; input: string }>;
-
-/**
- * @deprecated Use {@link ExtensionAttachTo} instead.
- * @public
- */
-export type ExtensionAttachToSpec = ExtensionAttachTo;
+export type ExtensionAttachTo = { id: string; input: string };
 
 /** @public */
 export interface Extension<TConfig, TConfigInput = TConfig> {
   $$type: '@backstage/Extension';
   readonly id: string;
-  readonly attachTo: ExtensionAttachToSpec;
+  readonly attachTo: ExtensionAttachTo;
   readonly disabled: boolean;
   readonly configSchema?: PortableSchema<TConfig, TConfigInput>;
 }
@@ -151,7 +143,7 @@ function resolveExtensionId(
 function resolveAttachTo(
   attachTo: ExtensionDefinitionAttachTo | ExtensionDefinitionAttachTo[],
   namespace?: string,
-): ExtensionAttachToSpec {
+): ExtensionAttachTo | ExtensionAttachTo[] {
   const resolveSpec = (
     spec: ExtensionDefinitionAttachTo,
   ): { id: string; input: string } => {
@@ -213,7 +205,7 @@ export function resolveExtensionDefinition<
 
   return {
     ...rest,
-    attachTo: resolveAttachTo(attachTo, namespace),
+    attachTo: resolveAttachTo(attachTo, namespace) as ExtensionAttachTo,
     $$type: '@backstage/Extension',
     version: internalDefinition.version,
     id,