diff --git a/.chronus/changes/python-flatten-property-tests-2026-3-2-7-34-49.md b/.chronus/changes/python-flatten-property-tests-2026-3-2-7-34-49.md
new file mode 100644
index 00000000000..7e184e0e2dd
--- /dev/null
+++ b/.chronus/changes/python-flatten-property-tests-2026-3-2-7-34-49.md
@@ -0,0 +1,7 @@
+---
+changeKind: internal
+packages:
+  - "@typespec/http-client-python"
+---
+
+Add test cases for flatten property with unknown type and read-only properties scenarios.
diff --git a/packages/http-client-python/generator/test/azure/mock_api_tests/asynctests/test_azure_client_generator_core_flatten_async.py b/packages/http-client-python/generator/test/azure/mock_api_tests/asynctests/test_azure_client_generator_core_flatten_async.py
index fe2f64f13db..b0c6c4786df 100644
--- a/packages/http-client-python/generator/test/azure/mock_api_tests/asynctests/test_azure_client_generator_core_flatten_async.py
+++ b/packages/http-client-python/generator/test/azure/mock_api_tests/asynctests/test_azure_client_generator_core_flatten_async.py
@@ -6,10 +6,12 @@
 import pytest
 from specs.azure.clientgenerator.core.flattenproperty.aio import FlattenPropertyClient
 from specs.azure.clientgenerator.core.flattenproperty.models import (
-    FlattenModel,
+    ChildFlattenModel,
     ChildModel,
+    FlattenModel,
+    FlattenUnknownModel,
     NestedFlattenModel,
-    ChildFlattenModel,
+    Solution,
 )
 
 
@@ -46,6 +48,22 @@ async def test_put_nested_flatten_model(client: FlattenPropertyClient):
     )
 
 
+@pytest.mark.asyncio
+async def test_put_flatten_unknown_model(client: FlattenPropertyClient):
+    result = await client.put_flatten_unknown_model(FlattenUnknownModel(name="foo"))
+    assert result.name == "test"
+    assert result.properties == {"key1": "value1", "key2": "value2"}
+
+
+@pytest.mark.asyncio
+async def test_put_flatten_read_only_model(client: FlattenPropertyClient):
+    result = await client.put_flatten_read_only_model(Solution({"name": "foo"}))
+    assert result.name == "foo"
+    assert result["solutionId"] == "solution1"
+    assert result["title"] == "Solution Title"
+    assert result["content"] == "Solution Content"
+
+
 @pytest.mark.asyncio  # ============test for compatibility ============
 async def test_dpg_model_common():
     flatten_model = FlattenModel(name="hello", properties=ChildModel(age=0, description="test"))
diff --git a/packages/http-client-python/generator/test/azure/mock_api_tests/test_azure_client_generator_core_flatten.py b/packages/http-client-python/generator/test/azure/mock_api_tests/test_azure_client_generator_core_flatten.py
index b1492f524ad..e90308509a2 100644
--- a/packages/http-client-python/generator/test/azure/mock_api_tests/test_azure_client_generator_core_flatten.py
+++ b/packages/http-client-python/generator/test/azure/mock_api_tests/test_azure_client_generator_core_flatten.py
@@ -6,10 +6,12 @@
 import pytest
 from specs.azure.clientgenerator.core.flattenproperty import FlattenPropertyClient
 from specs.azure.clientgenerator.core.flattenproperty.models import (
-    FlattenModel,
+    ChildFlattenModel,
     ChildModel,
+    FlattenModel,
+    FlattenUnknownModel,
     NestedFlattenModel,
-    ChildFlattenModel,
+    Solution,
 )
 
 
@@ -41,6 +43,20 @@ def test_put_nested_flatten_model(client: FlattenPropertyClient):
     )
 
 
+def test_put_flatten_unknown_model(client: FlattenPropertyClient):
+    result = client.put_flatten_unknown_model(FlattenUnknownModel(name="foo"))
+    assert result.name == "test"
+    assert result.properties == {"key1": "value1", "key2": "value2"}
+
+
+def test_put_flatten_read_only_model(client: FlattenPropertyClient):
+    result = client.put_flatten_read_only_model(Solution({"name": "foo"}))
+    assert result.name == "foo"
+    assert result["solutionId"] == "solution1"
+    assert result["title"] == "Solution Title"
+    assert result["content"] == "Solution Content"
+
+
 # ============test for compatibility ============
 def test_dpg_model_common():
     flatten_model = FlattenModel(name="hello", properties=ChildModel(age=0, description="test"))
diff --git a/packages/http-client-python/package-lock.json b/packages/http-client-python/package-lock.json
index 8035b620851..e8b8362d954 100644
--- a/packages/http-client-python/package-lock.json
+++ b/packages/http-client-python/package-lock.json
@@ -17,7 +17,7 @@
         "tsx": "^4.21.0"
       },
       "devDependencies": {
-        "@azure-tools/azure-http-specs": "0.1.0-alpha.38-dev.2",
+        "@azure-tools/azure-http-specs": "0.1.0-alpha.38-dev.4",
         "@azure-tools/typespec-autorest": "~0.65.0",
         "@azure-tools/typespec-azure-core": "~0.65.0",
         "@azure-tools/typespec-azure-resource-manager": "~0.65.0",
@@ -66,9 +66,9 @@
       }
     },
     "node_modules/@azure-tools/azure-http-specs": {
-      "version": "0.1.0-alpha.38-dev.2",
-      "resolved": "https://registry.npmjs.org/@azure-tools/azure-http-specs/-/azure-http-specs-0.1.0-alpha.38-dev.2.tgz",
-      "integrity": "sha512-rrxSHv70c5d9ZZQRN1xZ849/vzAFM7uHEkpjSNtKBBkx/6/2J2arSiltk4OP6xE/lqHPVPeANzbYQsL4b4wNZw==",
+      "version": "0.1.0-alpha.38-dev.4",
+      "resolved": "https://registry.npmjs.org/@azure-tools/azure-http-specs/-/azure-http-specs-0.1.0-alpha.38-dev.4.tgz",
+      "integrity": "sha512-RcMWlJoH/ZfFXR4X/nZ/L6siNDtYylYERikcF23JbJ1/SrYsFIS3IpdG4E1YlEMwwfgolL31CDM32+d6g+AViQ==",
       "dev": true,
       "license": "MIT",
       "dependencies": {
diff --git a/packages/http-client-python/package.json b/packages/http-client-python/package.json
index 39b23f709d7..7b85c019adb 100644
--- a/packages/http-client-python/package.json
+++ b/packages/http-client-python/package.json
@@ -82,7 +82,7 @@
     "@azure-tools/typespec-azure-resource-manager": "~0.65.0",
     "@azure-tools/typespec-azure-rulesets": "~0.65.0",
     "@azure-tools/typespec-client-generator-core": "~0.65.3",
-    "@azure-tools/azure-http-specs": "0.1.0-alpha.38-dev.2",
+    "@azure-tools/azure-http-specs": "0.1.0-alpha.38-dev.4",
     "@typespec/compiler": "^1.9.0",
     "@typespec/http": "^1.9.0",
     "@typespec/openapi": "^1.9.0",