diff --git a/README.md b/README.md
index cbc5d2f57..ce61b927b 100644
--- a/README.md
+++ b/README.md
@@ -139,9 +139,11 @@ pip install etna
 
 The default version doesn't contain all the dependencies, because some of them are needed only for specific models, e.g. Prophet, PyTorch.
 Available user extensions are the following:
-* `prophet`
-* `torch`
-* `wandb`
+* `prophet`: adds prophet model`,
+* `torch`: adds models based on neural nets,
+* `wandb`: adds wandb logger,
+* `auto`: adds AutoML functionality,
+* `classiciation`: adds time series classification functionality.
 
 Install extension:
 ```bash
diff --git a/etna/models/linear.py b/etna/models/linear.py
index bf29d7029..e16fdfae9 100644
--- a/etna/models/linear.py
+++ b/etna/models/linear.py
@@ -16,13 +16,19 @@
     from optuna.distributions import CategoricalDistribution
     from optuna.distributions import LogUniformDistribution
     from optuna.distributions import UniformDistribution
+else:
+    from unittest.mock import Mock
 
+    CategoricalDistribution = Mock  # type: ignore
+    UniformDistribution = Mock  # type: ignore
+    LogUniformDistribution = Mock  # type: ignore
 
-LINEAR_GRID: Dict[str, "BaseDistribution"] = {
+
+_LINEAR_GRID: Dict[str, "BaseDistribution"] = {
     "fit_intercept": CategoricalDistribution([False, True]),
 }
 
-ELASTIC_GRID: Dict[str, "BaseDistribution"] = {
+_ELASTIC_GRID: Dict[str, "BaseDistribution"] = {
     "fit_intercept": CategoricalDistribution([False, True]),
     "l1_ratio": UniformDistribution(0, 1),
     "alpha": LogUniformDistribution(low=1e-5, high=1e3),
@@ -92,7 +98,7 @@ def params_to_tune(self) -> Dict[str, "BaseDistribution"]:
         :
             Grid to tune.
         """
-        return LINEAR_GRID
+        return _LINEAR_GRID
 
 
 class ElasticPerSegmentModel(
@@ -155,7 +161,7 @@ def params_to_tune(self) -> Dict[str, "BaseDistribution"]:
         :
             Grid to tune.
         """
-        return ELASTIC_GRID
+        return _ELASTIC_GRID
 
 
 class LinearMultiSegmentModel(
@@ -195,7 +201,7 @@ def params_to_tune(self) -> Dict[str, "BaseDistribution"]:
         :
             Grid to tune.
         """
-        return LINEAR_GRID
+        return _LINEAR_GRID
 
 
 class ElasticMultiSegmentModel(
@@ -258,4 +264,4 @@ def params_to_tune(self) -> Dict[str, "BaseDistribution"]:
         :
             Grid to tune.
         """
-        return ELASTIC_GRID
+        return _ELASTIC_GRID
diff --git a/examples/automl.ipynb b/examples/automl.ipynb
index e01db8f5f..c1713521d 100644
--- a/examples/automl.ipynb
+++ b/examples/automl.ipynb
@@ -50,6 +50,17 @@
     "HORIZON = 14"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "e5c2c568",
+   "metadata": {},
+   "source": [
+    "Many features from this notebook require `auto` extension. You can install it by the command:\n",
+    "```bash\n",
+    "pip install etna[auto]\n",
+    "```"
+   ]
+  },
   {
    "cell_type": "markdown",
    "id": "33ad7417",