From 4a936276746d06199c8665ece5179b5fe51bec0b Mon Sep 17 00:00:00 2001
From: Gerardo Lecaros <10088504+glecaros@users.noreply.github.com>
Date: Wed, 19 Aug 2026 19:03:30 +0000
Subject: [PATCH] Fixing issue where durations encoded as milliseconds would
 not properly encode the durations as the proper type.

---
 ...iseconds-example-serialization-2026-8-19-18-30-0.md |  7 +++++++
 packages/compiler/src/lib/examples.ts                  |  6 ++++++
 packages/compiler/test/decorators/examples.test.ts     | 10 ++++++++++
 3 files changed, 23 insertions(+)
 create mode 100644 .chronus/changes/fix-duration-milliseconds-example-serialization-2026-8-19-18-30-0.md

diff --git a/.chronus/changes/fix-duration-milliseconds-example-serialization-2026-8-19-18-30-0.md b/.chronus/changes/fix-duration-milliseconds-example-serialization-2026-8-19-18-30-0.md
new file mode 100644
index 00000000000..85335fcc319
--- /dev/null
+++ b/.chronus/changes/fix-duration-milliseconds-example-serialization-2026-8-19-18-30-0.md
@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/compiler"
+---
+
+Fix `duration` example values being serialized verbatim as an ISO 8601 string instead of a numeric value when encoded with `@encode("milliseconds", ...)`
diff --git a/packages/compiler/src/lib/examples.ts b/packages/compiler/src/lib/examples.ts
index 48f3dbc6455..9445029cd97 100644
--- a/packages/compiler/src/lib/examples.ts
+++ b/packages/compiler/src/lib/examples.ts
@@ -310,6 +310,12 @@ const ScalarSerializers = {
         } else {
           return duration.total({ unit: "seconds" });
         }
+      case "milliseconds":
+        if (isInteger(encodeAs.type)) {
+          return Math.floor(duration.total({ unit: "milliseconds" }));
+        } else {
+          return duration.total({ unit: "milliseconds" });
+        }
       default:
         return duration.toString();
     }
diff --git a/packages/compiler/test/decorators/examples.test.ts b/packages/compiler/test/decorators/examples.test.ts
index 34753df117a..c3877df2241 100644
--- a/packages/compiler/test/decorators/examples.test.ts
+++ b/packages/compiler/test/decorators/examples.test.ts
@@ -477,6 +477,16 @@ describe("json serialization of examples", () => {
             expect: 0.5,
             encode: `@encode("seconds", float32)`,
           },
+          {
+            value: `duration.fromISO("PT5M")`,
+            expect: 300000,
+            encode: `@encode("milliseconds", int32)`,
+          },
+          {
+            value: `duration.fromISO("PT0.5S")`,
+            expect: 500,
+            encode: `@encode("milliseconds", float32)`,
+          },
         ],
       ],
     ];