diff --git a/.chronus/changes/specs-noAuth-2026-0-6-16-4-0.md b/.chronus/changes/specs-noAuth-2026-0-6-16-4-0.md
new file mode 100644
index 00000000000..536fd92c327
--- /dev/null
+++ b/.chronus/changes/specs-noAuth-2026-0-6-16-4-0.md
@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/http-specs"
+---
+
+Add test for services that accept `NoAuth` unioned with other auth type
\ No newline at end of file
diff --git a/cspell.yaml b/cspell.yaml
index d00edc56709..a726a71c8f9 100644
--- a/cspell.yaml
+++ b/cspell.yaml
@@ -166,6 +166,7 @@ words:
   - nexted
   - nihao
   - nint
+  - noauth
   - NODEFS
   - noformat
   - nologo
diff --git a/packages/http-specs/spec-summary.md b/packages/http-specs/spec-summary.md
index a265b83066f..a943273eea8 100644
--- a/packages/http-specs/spec-summary.md
+++ b/packages/http-specs/spec-summary.md
@@ -39,6 +39,18 @@ Expect error code 403 and error body:
 
 Expects header 'Authorization': 'SharedAccessKey valid-key'
 
+### Authentication_Noauth_Union_validNoAuth
+
+- Endpoint: `get /authentication/noauth/union/valid`
+
+Expects no authentication. The server accepts requests without any authentication header.
+
+### Authentication_Noauth_Union_validToken
+
+- Endpoint: `get /authentication/noauth/union/validtoken`
+
+Expects header 'authorization': 'Bearer https://security.microsoft.com/.default'
+
 ### Authentication_OAuth2_invalid
 
 - Endpoint: `get /authentication/oauth2/invalid`
diff --git a/packages/http-specs/specs/authentication/noauth/union/main.tsp b/packages/http-specs/specs/authentication/noauth/union/main.tsp
new file mode 100644
index 00000000000..b7b208a31b2
--- /dev/null
+++ b/packages/http-specs/specs/authentication/noauth/union/main.tsp
@@ -0,0 +1,30 @@
+import "@typespec/http";
+import "@typespec/spector";
+
+using Http;
+using Spector;
+
+@scenarioService("/authentication/noauth/union")
+@doc("Illustrates clients generated with NoAuth and OAuth2 authentication union.")
+@useAuth(NoAuth | OAuth2Auth<[MyFlow]>)
+namespace Authentication.Noauth.Union;
+
+model MyFlow {
+  type: OAuth2FlowType.implicit;
+  authorizationUrl: "https://login.microsoftonline.com/common/oauth2/authorize";
+  scopes: ["https://security.microsoft.com/.default"];
+}
+
+@scenario
+@scenarioDoc("Expects no authentication. The server accepts requests without any authentication header.")
+@doc("Check whether client can make a request without authentication")
+@get
+@route("/valid")
+op validNoAuth(): NoContentResponse;
+
+@scenario
+@scenarioDoc("Expects header 'authorization': 'Bearer https://security.microsoft.com/.default'")
+@doc("Check whether client is authenticated with OAuth2 token")
+@get
+@route("/validtoken")
+op validToken(): NoContentResponse;
diff --git a/packages/http-specs/specs/authentication/noauth/union/mockapi.ts b/packages/http-specs/specs/authentication/noauth/union/mockapi.ts
new file mode 100644
index 00000000000..4aee49b0c56
--- /dev/null
+++ b/packages/http-specs/specs/authentication/noauth/union/mockapi.ts
@@ -0,0 +1,27 @@
+import { passOnSuccess, ScenarioMockApi } from "@typespec/spec-api";
+
+export const Scenarios: Record<string, ScenarioMockApi> = {};
+
+Scenarios.Authentication_Noauth_Union_validNoAuth = passOnSuccess({
+  uri: `/authentication/noauth/union/valid`,
+  method: "get",
+  request: {},
+  response: {
+    status: 204,
+  },
+  kind: "MockApiDefinition",
+});
+
+Scenarios.Authentication_Noauth_Union_validToken = passOnSuccess({
+  uri: `/authentication/noauth/union/validtoken`,
+  method: "get",
+  request: {
+    headers: {
+      authorization: "Bearer https://security.microsoft.com/.default",
+    },
+  },
+  response: {
+    status: 204,
+  },
+  kind: "MockApiDefinition",
+});