diff --git a/.chronus/changes/copilot-add-array-encoding-test-case-2026-0-12-6-2-30.md b/.chronus/changes/copilot-add-array-encoding-test-case-2026-0-12-6-2-30.md
new file mode 100644
index 00000000000..7ffefca44cf
--- /dev/null
+++ b/.chronus/changes/copilot-add-array-encoding-test-case-2026-0-12-6-2-30.md
@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/http-specs"
+---
+
+Add test case for ArrayEncoding with extensible union
\ No newline at end of file
diff --git a/packages/http-specs/spec-summary.md b/packages/http-specs/spec-summary.md
index a265b83066f..31fc2dc0877 100644
--- a/packages/http-specs/spec-summary.md
+++ b/packages/http-specs/spec-summary.md
@@ -168,6 +168,27 @@ Expected response body:
 }
 ```
 
+### Encode_Array_Property_pipeDelimitedEnumElement
+
+- Endpoint: `post /encode/array/property/pipe-delimited-enum-element`
+
+Test operation with request and response model contains an extensible enum array property with pipeDelimited encode.
+Expected request body:
+
+```json
+{
+  "value": "blue|red|green"
+}
+```
+
+Expected response body:
+
+```json
+{
+  "value": "blue|red|green"
+}
+```
+
 ### Encode_Array_Property_spaceDelimited
 
 - Endpoint: `post /encode/array/property/space-delimited`
diff --git a/packages/http-specs/specs/encode/array/main.tsp b/packages/http-specs/specs/encode/array/main.tsp
index 4e707eeb41d..8f49a7e999f 100644
--- a/packages/http-specs/specs/encode/array/main.tsp
+++ b/packages/http-specs/specs/encode/array/main.tsp
@@ -8,6 +8,13 @@ using Spector;
 @scenarioService("/encode/array")
 namespace Encode.Array;
 
+union Color {
+  string,
+  Blue: "blue",
+  Red: "red",
+  Green: "green",
+}
+
 model CommaDelimitedArrayProperty {
   @encode(ArrayEncoding.commaDelimited)
   value: string[];
@@ -28,6 +35,11 @@ model NewlineDelimitedArrayProperty {
   value: string[];
 }
 
+model PipeDelimitedArrayEnumElementProperty {
+  @encode(ArrayEncoding.pipeDelimited)
+  value: Color[];
+}
+
 @route("/property")
 namespace Property {
   @route("/comma-delimited")
@@ -109,4 +121,26 @@ namespace Property {
     """)
   @post
   op newlineDelimited(@body body: NewlineDelimitedArrayProperty): NewlineDelimitedArrayProperty;
+
+  @route("/pipe-delimited-enum-element")
+  @scenario
+  @scenarioDoc("""
+    Test operation with request and response model contains an extensible enum array property with pipeDelimited encode.
+    Expected request body:
+    ```json
+    {
+      "value": "blue|red|green"
+    }
+    ```
+    Expected response body:
+    ```json
+    {
+      "value": "blue|red|green"
+    }
+    ```
+    """)
+  @post
+  op pipeDelimitedEnumElement(
+    @body body: PipeDelimitedArrayEnumElementProperty,
+  ): PipeDelimitedArrayEnumElementProperty;
 }
diff --git a/packages/http-specs/specs/encode/array/mockapi.ts b/packages/http-specs/specs/encode/array/mockapi.ts
index 8b22eeb67ea..9ed503e474c 100644
--- a/packages/http-specs/specs/encode/array/mockapi.ts
+++ b/packages/http-specs/specs/encode/array/mockapi.ts
@@ -41,3 +41,8 @@ Scenarios.Encode_Array_Property_newlineDelimited = createPropertyServerTests(
   "/encode/array/property/newline-delimited",
   "\n",
 );
+
+Scenarios.Encode_Array_Property_pipeDelimitedEnumElement = createPropertyServerTests(
+  "/encode/array/property/pipe-delimited-enum-element",
+  "|",
+);