diff --git a/sagemaker-serve/pyproject.toml b/sagemaker-serve/pyproject.toml
index 58c3c5b97e..4b1d6c475f 100644
--- a/sagemaker-serve/pyproject.toml
+++ b/sagemaker-serve/pyproject.toml
@@ -27,7 +27,12 @@ dependencies = [
     "boto3>=1.42.2,<2.0",
     "botocore>=1.35.75,<2.0",
     "deepdiff",
-    "mlflow",
+    "mlflow-skinny",
+    # Declared explicitly because full mlflow used to supply it transitively
+    # (mlflow requires docker>=4.0.0,<8; mlflow-skinny does not). It is imported at
+    # module scope by sagemaker.serve.mode.local_container_mode, which sagemaker.serve
+    # imports eagerly, so a missing docker breaks `import sagemaker.serve` outright.
+    "docker>=5.0.2,<8.0.0",
     "sagemaker_schema_inference_artifacts",
     "pytest",
     "tqdm",
@@ -39,6 +44,11 @@ dependencies = [
 ]
 
 [project.optional-dependencies]
+# Full MLflow. The client only needs the tracking/registry APIs from mlflow-skinny;
+# the full MLflow model-flavor loaders (mlflow.pyfunc/sklearn/pytorch/...) are used
+# only by the container-side inference handlers that run inside the DLC. Install this
+# extra to pull in the full MLflow package locally.
+full = ["mlflow"]
 test = [
     "pytest",
     "pytest-cov",
diff --git a/sagemaker-serve/tests/unit/test_declared_dependencies.py b/sagemaker-serve/tests/unit/test_declared_dependencies.py
new file mode 100644
index 0000000000..8a5b1aea14
--- /dev/null
+++ b/sagemaker-serve/tests/unit/test_declared_dependencies.py
@@ -0,0 +1,138 @@
+"""Every module-level third-party import must have a declared distribution.
+
+Regression guard for #6152. Switching ``mlflow`` to ``mlflow-skinny`` silently dropped
+``docker``: full mlflow requires ``docker>=4.0.0,<8`` while mlflow-skinny requires
+nothing of the sort. ``docker`` is imported at module scope by
+``sagemaker.serve.mode.local_container_mode``, which ``sagemaker.serve.__init__``
+imports eagerly, so losing it breaks ``import sagemaker.serve`` outright. Nothing went
+red until a CI runner happened not to have ``docker`` already installed, which is
+exactly the kind of gap a declared-dependency check closes.
+
+The check is deliberately limited to *module-level* imports. Imports nested inside a
+function are opt-in code paths (matplotlib for plotting, sklearn for framework
+detection) and are allowed to rely on an undeclared package.
+"""
+
+from __future__ import absolute_import
+
+import ast
+import os
+import re
+import sys
+from pathlib import Path
+
+import pytest
+
+SERVE_ROOT = Path(__file__).resolve().parents[2]
+REPO_ROOT = SERVE_ROOT.parent
+SERVE_SRC = SERVE_ROOT / "src"
+
+# sagemaker-serve depends on sagemaker-core and sagemaker-train, so anything those two
+# declare is also importable from serve.
+PYPROJECTS = (
+    SERVE_ROOT / "pyproject.toml",
+    REPO_ROOT / "sagemaker-core" / "pyproject.toml",
+    REPO_ROOT / "sagemaker-train" / "pyproject.toml",
+)
+
+# Import name -> distribution name, for the cases where they differ.
+IMPORT_TO_DISTRIBUTION = {
+    "yaml": "pyyaml",
+}
+
+# Modules provided by the runtime environment rather than by our wheels.
+EXEMPT_IMPORTS = {
+    # Injected by the Triton Python backend inside the serving container; it is not
+    # importable from the SDK and must never be a declared dependency.
+    "triton_python_backend_utils",
+}
+
+FIRST_PARTY = {"sagemaker"}
+
+# Matches the top-level `dependencies = [...]` array. The optional-dependency arrays are
+# keyed by extra name (`full`, `test`, `dev`), so they cannot match this pattern.
+_DEPENDENCIES_ARRAY = re.compile(r"^dependencies = \[(.*?)^\]", re.MULTILINE | re.DOTALL)
+
+
+def _normalize(name):
+    """Normalize a distribution name per PEP 503."""
+    return re.sub(r"[-_.]+", "-", name).lower()
+
+
+def _declared_distributions():
+    """Return the normalized distribution names declared across the three packages."""
+    declared = set()
+    for pyproject in PYPROJECTS:
+        match = _DEPENDENCIES_ARRAY.search(pyproject.read_text(encoding="utf-8"))
+        assert match, "no top-level dependencies array found in {}".format(pyproject)
+        for line in match.group(1).splitlines():
+            line = line.split("#", 1)[0].strip().rstrip(",").strip()
+            if not line:
+                continue
+            requirement = ast.literal_eval(line)
+            # Strip extras, version specifiers and environment markers.
+            name = re.split(r"[\[<>=!~;\s]", requirement, maxsplit=1)[0]
+            declared.add(_normalize(name))
+    return declared
+
+
+def _module_level_imports():
+    """Map each module-level third-party import to the files that import it."""
+    imports = {}
+    for dirpath, _, filenames in os.walk(SERVE_SRC):
+        for filename in filenames:
+            if not filename.endswith(".py"):
+                continue
+            path = Path(dirpath) / filename
+            try:
+                tree = ast.parse(path.read_text(encoding="utf-8"))
+            except (SyntaxError, UnicodeDecodeError):
+                continue
+            for node in tree.body:  # module level only, by construction
+                if isinstance(node, ast.Import):
+                    names = [alias.name for alias in node.names]
+                elif isinstance(node, ast.ImportFrom) and not node.level and node.module:
+                    names = [node.module]
+                else:
+                    continue
+                for name in names:
+                    top = name.split(".")[0]
+                    if top in sys.stdlib_module_names or top in FIRST_PARTY:
+                        continue
+                    if top in EXEMPT_IMPORTS:
+                        continue
+                    imports.setdefault(top, set()).add(str(path.relative_to(REPO_ROOT)))
+    return imports
+
+
+def test_module_level_imports_are_declared_dependencies():
+    """Fail if sagemaker-serve imports a package none of the three packages declare."""
+    declared = _declared_distributions()
+    undeclared = {}
+    for module, files in _module_level_imports().items():
+        distribution = IMPORT_TO_DISTRIBUTION.get(module, module)
+        if _normalize(distribution) not in declared:
+            undeclared[module] = sorted(files)
+
+    assert not undeclared, "module-level imports with no declared distribution: " + "; ".join(
+        "{} (imported by {})".format(module, ", ".join(files))
+        for module, files in sorted(undeclared.items())
+    )
+
+
+def test_docker_is_declared():
+    """Pin the specific regression from #6152 so it cannot silently come back.
+
+    ``docker`` has to be a hard dependency, not an extra: the import sits at module
+    scope on the eager path out of ``sagemaker.serve.__init__``.
+    """
+    assert "docker" in _declared_distributions()
+
+
+@pytest.mark.parametrize(
+    "module",
+    ["docker", "numpy", "pandas", "yaml"],
+)
+def test_sanity_known_module_level_imports_are_detected(module):
+    """Guard the detector itself: these are known module-level imports in serve."""
+    assert module in _module_level_imports()
diff --git a/sagemaker-train/pyproject.toml b/sagemaker-train/pyproject.toml
index a78dadfac1..51bf2d60f9 100644
--- a/sagemaker-train/pyproject.toml
+++ b/sagemaker-train/pyproject.toml
@@ -40,7 +40,7 @@ dependencies = [
     "paramiko>=2.11.0",
     "jinja2>=3.0,<4.0",
     "sagemaker-mlflow>=0.0.1,<1.0.0",
-    "mlflow>=3.0.0,<4.0.0",
+    "mlflow-skinny>=3.0.0,<4.0.0",
     "nest_asyncio>=1.5.0",
     "requests>=2.28.0",
     "pydantic>=2.0.0",
@@ -52,6 +52,10 @@ Homepage = "https://github.com/aws/sagemaker-python-sdk"
 [project.optional-dependencies]
 rft-strands = ["strands-agents"]
 rft-langchain = ["httpx>=0.24.0"]
+# Full MLflow (model flavors, pyfunc/sklearn/pytorch/... loaders). The client only
+# needs the tracking/registry APIs from mlflow-skinny; install this extra when you
+# want the full MLflow package (e.g. to load MLflow model flavors locally).
+full = ["mlflow>=3.0.0,<4.0.0"]
 test = [
     "pytest",
     "pytest-cov",