diff --git a/tests/pytests/pkg/integration/test_libyaml.py b/tests/pytests/pkg/integration/test_libyaml.py
new file mode 100644
index 000000000000..900d9b39fb71
--- /dev/null
+++ b/tests/pytests/pkg/integration/test_libyaml.py
@@ -0,0 +1,134 @@
+"""
+Verify the onedir bundle ships a libyaml-linked PyYAML.
+
+Regression cover for #69907 / PR #69950 (3006.x) and #69949 (3008.x):
+the Linux onedir build was source-compiling PyYAML under a relenv toolchain
+that has no libyaml, so `yaml.CSafeLoader`/`yaml.CSafeDumper` were absent
+and every YAML load fell back to the ~10-20x slower pure-Python parser.
+
+The test asserts the invariant that matches whatever salt is installed at
+run time, so it works uniformly across the install / upgrade / downgrade
+package-test flavors:
+
+- install / post-upgrade: current onedir is on disk, expect libyaml present
+- post-downgrade: previous onedir is on disk. That release predates the
+  fix, so expect libyaml absent (documenting the pre-fix state so a silent
+  regression on the previous branch is still caught).
+"""
+
+import subprocess
+import sys
+import textwrap
+
+import pytest
+
+
+@pytest.fixture
+def python_script_bin(install_salt):
+    return install_salt.binary_paths["python"]
+
+
+@pytest.fixture
+def libyaml_expected(install_salt):
+    """Current onedir (install/upgrade) ships libyaml; the previous release
+    (post-downgrade validation) predates PR #69950 and does not."""
+    return not install_salt.use_prev_version
+
+
+@pytest.fixture
+def check_libyaml_file(tmp_path):
+    script_path = tmp_path / "check_libyaml.py"
+    script_path.write_text(
+        textwrap.dedent(
+            """
+        import sys
+        import yaml
+
+        assert hasattr(yaml, "CSafeLoader"), "yaml.CSafeLoader missing"
+        assert hasattr(yaml, "CSafeDumper"), "yaml.CSafeDumper missing"
+        assert hasattr(yaml, "CLoader"), "yaml.CLoader missing"
+        assert hasattr(yaml, "CDumper"), "yaml.CDumper missing"
+
+        import _yaml  # noqa: F401  # PyYAML C extension
+
+        loader = yaml.CSafeLoader("key: value\\n")
+        try:
+            data = loader.get_single_data()
+        finally:
+            loader.dispose()
+        assert data == {"key": "value"}, data
+        sys.exit(0)
+        """
+        )
+    )
+    return script_path
+
+
+@pytest.mark.skipif(
+    not sys.platform.startswith("linux"),
+    reason="Only the Linux onedir build passes --no-binary=:all:; "
+    "Windows/macOS already pick libyaml-linked wheels.",
+)
+def test_libyaml_matches_installed_version(
+    install_salt, python_script_bin, check_libyaml_file, libyaml_expected
+):
+    ret = install_salt.proc.run(
+        *(python_script_bin + [str(check_libyaml_file)]),
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        check=False,
+        universal_newlines=True,
+    )
+    if libyaml_expected:
+        assert ret.returncode == 0, (
+            f"libyaml expected present in the current onedir but the probe "
+            f"failed:\n{ret.stderr}"
+        )
+    else:
+        assert ret.returncode != 0, (
+            "libyaml unexpectedly present in the previous-release onedir. "
+            "If PR #69950 was backported earlier than 3006.28, drop this "
+            "test's downgrade branch."
+        )
+
+
+@pytest.mark.skipif(
+    not sys.platform.startswith("linux"),
+    reason="Only the Linux onedir build passes --no-binary=:all:; "
+    "Windows/macOS already pick libyaml-linked wheels.",
+)
+def test_salt_yamlloader_matches_installed_version(
+    install_salt, python_script_bin, tmp_path, libyaml_expected
+):
+    script_path = tmp_path / "check_yamlloader.py"
+    script_path.write_text(
+        textwrap.dedent(
+            """
+        import sys
+        import yaml
+        import salt.utils.yamlloader
+
+        sys.exit(0 if salt.utils.yamlloader.BaseLoader is getattr(yaml, "CSafeLoader", None) else 1)
+        """
+        )
+    )
+    ret = install_salt.proc.run(
+        *(python_script_bin + [str(script_path)]),
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        check=False,
+        universal_newlines=True,
+    )
+    if libyaml_expected:
+        assert ret.returncode == 0, (
+            "salt.utils.yamlloader.BaseLoader should be yaml.CSafeLoader in "
+            "the current onedir; it resolved to the pure-Python loader "
+            "instead."
+        )
+    else:
+        assert ret.returncode != 0, (
+            "salt.utils.yamlloader.BaseLoader unexpectedly resolves to "
+            "yaml.CSafeLoader in the previous-release onedir. If PR #69950 "
+            "was backported earlier than 3006.28, drop this test's downgrade "
+            "branch."
+        )