diff --git a/.github/workflows/test-upstream.yaml b/.github/workflows/test-upstream.yaml
index 1aab649c..c767647a 100644
--- a/.github/workflows/test-upstream.yaml
+++ b/.github/workflows/test-upstream.yaml
@@ -118,7 +118,10 @@ jobs:
           python-version: ${{ matrix.python-version }}
 
       - name: Install poetry
-        run: pipx install poetry
+        run: pipx install poetry==1.*
+
+      - name: Check Poetry version
+        run: poetry --version
 
       - name: Install dynamic versioning plugin
         run: poetry self add "poetry-dynamic-versioning[plugin]"
diff --git a/README.md b/README.md
index 4020b7c9..d48c3cc2 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@
 [![PyPIDownloadsMonth](https://img.shields.io/pypi/dm/linkml-runtime?logo=PyPI&color=blue)](https://pypi.org/project/linkml-runtime)
 [![codecov](https://codecov.io/gh/linkml/linkml-runtime/branch/main/graph/badge.svg?token=FOBHNSK5WG)](https://codecov.io/gh/linkml/linkml-runtime)
 
-Runtime support for linkml generated data classes
+Runtime support for linkml generated data classes.
 
 ## About
 
diff --git a/linkml_runtime/utils/dataclass_extensions_376.py b/linkml_runtime/utils/dataclass_extensions_376.py
new file mode 100644
index 00000000..4321855d
--- /dev/null
+++ b/linkml_runtime/utils/dataclass_extensions_376.py
@@ -0,0 +1,15 @@
+import sys
+import warnings
+import dataclasses
+
+warnings.warn(
+    "The LinkML dataclass extension patch is deprecated and will be removed in a future release.\n"
+    "If you're currently using Python < 3.13, where this patch still applies, you should:\n"
+    "  • Upgrade your LinkML tooling to version >= 1.9.0 (which no longer needs this patch), OR\n"
+    "  • Migrate to Pydantic models if you're using LinkML's generated classes at runtime.\n",
+    DeprecationWarning,
+    stacklevel=2
+)
+
+dataclasses_init_fn_with_kwargs = dataclasses._init_fn
+DC_CREATE_FN = False
\ No newline at end of file
diff --git a/tests/test_issues/test_dataclass_extensions_376.py b/tests/test_issues/test_dataclass_extensions_376.py
new file mode 100644
index 00000000..093a233e
--- /dev/null
+++ b/tests/test_issues/test_dataclass_extensions_376.py
@@ -0,0 +1,27 @@
+import sys
+import pytest
+import importlib.util
+import dataclasses
+
+
+def import_patch_module():
+    """Fresh import to ensure warning is triggered"""
+    spec = importlib.util.find_spec("linkml_runtime.utils.dataclass_extensions_376")
+    mod = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(mod)
+    return mod
+
+def test_patch_module_emits_deprecation_warning():
+    """All Python versions: emits DeprecationWarning and defines compatibility symbols"""
+    with pytest.warns(DeprecationWarning):
+        mod = import_patch_module()
+
+    assert hasattr(mod, "DC_CREATE_FN")
+    assert hasattr(mod, "dataclasses_init_fn_with_kwargs")
+    assert mod.DC_CREATE_FN is False
+
+    # Check consistency with actual dataclasses module
+    init_fn = getattr(dataclasses, "_init_fn", None)
+    assert mod.dataclasses_init_fn_with_kwargs == init_fn
+
+