diff --git a/docs/user-guide/classifier-types.md b/docs/user-guide/classifier-types.md
index ddefbd08..ce2a7443 100644
--- a/docs/user-guide/classifier-types.md
+++ b/docs/user-guide/classifier-types.md
@@ -2,6 +2,8 @@
 
 JABS supports three machine learning classifier types: **Random Forest**, **CatBoost**, and **XGBoost**. Each has different characteristics that may make it more suitable for your specific use case.
 
+> **Classifier type vs. classifier mode:** This page covers the machine learning *algorithm*. Separately, JABS can train one binary classifier per behavior (the default) or a single classifier across all behaviors at once. See [Multi-Class Classification (Preview)](multi-class.md) for the experimental multi-class mode.
+
 ## Random Forest (Default)
 
 Random Forest is the default classifier and a good starting point for most users.
diff --git a/docs/user-guide/multi-class.md b/docs/user-guide/multi-class.md
new file mode 100644
index 00000000..79404456
--- /dev/null
+++ b/docs/user-guide/multi-class.md
@@ -0,0 +1,64 @@
+# Multi-Class Classification (Preview)
+
+> **Preview feature.** Multi-class mode is under active development and is provided
+> as a preview. Some capabilities are not yet available, and its behavior, stored
+> data, and settings may change in upcoming JABS releases. Binary mode (the
+> default) is unaffected.
+
+## Overview
+
+By default, JABS trains one **binary** classifier per behavior: each classifier
+predicts whether a given frame contains that behavior or not, and behaviors are
+independent of one another.
+
+**Multi-class mode** instead trains a *single* classifier across all annotated
+behaviors at once. Each frame is assigned to exactly one class: one of your
+behaviors, or the reserved **None** (background) class. This is appropriate when
+your behaviors are **mutually exclusive** - that is, an animal cannot be doing two
+of them on the same frame.
+
+## Enabling multi-class mode
+
+Open **Project Settings** and set **Classifier Mode** to **Multi-class (Preview)**.
+The setting is stored with the project, and the default for all projects remains
+**Binary**.
+
+Switching an existing project to multi-class mode is blocked if any frames are
+labeled with two or more behaviors simultaneously; JABS lists the conflicting
+videos so the overlaps can be resolved first.
+
+## Labeling for multi-class
+
+- Label each behavior as usual. Because classes are mutually exclusive, labeling a
+  frame with one behavior clears any other behavior label on that frame.
+- The **None** button records an explicit *background* label - frames that are
+  none of your behaviors. In multi-class mode these explicit negatives are stored
+  on a reserved **None** track rather than as "not behavior" on an individual
+  behavior. The **Label Summary** reflects this: it shows the selected behavior's
+  count and a **None** count (instead of "Behavior" / "Not Behavior").
+- Only explicitly labeled frames (a behavior or **None**) are used for training;
+  unlabeled frames are ignored.
+
+## Known limitations (preview)
+
+- **No prediction post-processing.** The post-processing step available for binary
+  predictions is not yet applied to multi-class predictions. Multi-class
+  predictions are shown and saved as raw (argmax) results only.
+- **Project-level training settings.** Window size and label balancing apply at the
+  project level for the single shared classifier rather than per behavior. Some
+  per-behavior options available in binary mode (for example, selective symmetric
+  augmentation per behavior) are not yet available in multi-class mode.
+- **Mutual exclusivity required.** Behaviors must not overlap on the same frame.
+  Overlapping labels must be resolved before switching to multi-class mode or
+  training.
+- **Migration.** Existing binary classifiers are not converted to multi-class
+  format (or vice versa); the two modes maintain separate classifier and
+  prediction files within a project.
+- **Format stability.** The on-disk representation and available settings for
+  multi-class mode may change in future releases.
+
+## Command-line use
+
+`jabs-classify` auto-detects whether a saved classifier is binary or multi-class
+and dispatches accordingly, so existing command-line workflows continue to work
+with multi-class classifiers without additional flags.
\ No newline at end of file
diff --git a/src/jabs/resources/docs/user_guide/classifier-types.md b/src/jabs/resources/docs/user_guide/classifier-types.md
index ddefbd08..ce2a7443 100644
--- a/src/jabs/resources/docs/user_guide/classifier-types.md
+++ b/src/jabs/resources/docs/user_guide/classifier-types.md
@@ -2,6 +2,8 @@
 
 JABS supports three machine learning classifier types: **Random Forest**, **CatBoost**, and **XGBoost**. Each has different characteristics that may make it more suitable for your specific use case.
 
+> **Classifier type vs. classifier mode:** This page covers the machine learning *algorithm*. Separately, JABS can train one binary classifier per behavior (the default) or a single classifier across all behaviors at once. See [Multi-Class Classification (Preview)](multi-class.md) for the experimental multi-class mode.
+
 ## Random Forest (Default)
 
 Random Forest is the default classifier and a good starting point for most users.
diff --git a/src/jabs/resources/docs/user_guide/multi-class.md b/src/jabs/resources/docs/user_guide/multi-class.md
new file mode 100644
index 00000000..79404456
--- /dev/null
+++ b/src/jabs/resources/docs/user_guide/multi-class.md
@@ -0,0 +1,64 @@
+# Multi-Class Classification (Preview)
+
+> **Preview feature.** Multi-class mode is under active development and is provided
+> as a preview. Some capabilities are not yet available, and its behavior, stored
+> data, and settings may change in upcoming JABS releases. Binary mode (the
+> default) is unaffected.
+
+## Overview
+
+By default, JABS trains one **binary** classifier per behavior: each classifier
+predicts whether a given frame contains that behavior or not, and behaviors are
+independent of one another.
+
+**Multi-class mode** instead trains a *single* classifier across all annotated
+behaviors at once. Each frame is assigned to exactly one class: one of your
+behaviors, or the reserved **None** (background) class. This is appropriate when
+your behaviors are **mutually exclusive** - that is, an animal cannot be doing two
+of them on the same frame.
+
+## Enabling multi-class mode
+
+Open **Project Settings** and set **Classifier Mode** to **Multi-class (Preview)**.
+The setting is stored with the project, and the default for all projects remains
+**Binary**.
+
+Switching an existing project to multi-class mode is blocked if any frames are
+labeled with two or more behaviors simultaneously; JABS lists the conflicting
+videos so the overlaps can be resolved first.
+
+## Labeling for multi-class
+
+- Label each behavior as usual. Because classes are mutually exclusive, labeling a
+  frame with one behavior clears any other behavior label on that frame.
+- The **None** button records an explicit *background* label - frames that are
+  none of your behaviors. In multi-class mode these explicit negatives are stored
+  on a reserved **None** track rather than as "not behavior" on an individual
+  behavior. The **Label Summary** reflects this: it shows the selected behavior's
+  count and a **None** count (instead of "Behavior" / "Not Behavior").
+- Only explicitly labeled frames (a behavior or **None**) are used for training;
+  unlabeled frames are ignored.
+
+## Known limitations (preview)
+
+- **No prediction post-processing.** The post-processing step available for binary
+  predictions is not yet applied to multi-class predictions. Multi-class
+  predictions are shown and saved as raw (argmax) results only.
+- **Project-level training settings.** Window size and label balancing apply at the
+  project level for the single shared classifier rather than per behavior. Some
+  per-behavior options available in binary mode (for example, selective symmetric
+  augmentation per behavior) are not yet available in multi-class mode.
+- **Mutual exclusivity required.** Behaviors must not overlap on the same frame.
+  Overlapping labels must be resolved before switching to multi-class mode or
+  training.
+- **Migration.** Existing binary classifiers are not converted to multi-class
+  format (or vice versa); the two modes maintain separate classifier and
+  prediction files within a project.
+- **Format stability.** The on-disk representation and available settings for
+  multi-class mode may change in future releases.
+
+## Command-line use
+
+`jabs-classify` auto-detects whether a saved classifier is binary or multi-class
+and dispatches accordingly, so existing command-line workflows continue to work
+with multi-class classifiers without additional flags.
\ No newline at end of file
diff --git a/src/jabs/ui/dialogs/user_guide_dialog.py b/src/jabs/ui/dialogs/user_guide_dialog.py
index 7a12a008..32cd8087 100644
--- a/src/jabs/ui/dialogs/user_guide_dialog.py
+++ b/src/jabs/ui/dialogs/user_guide_dialog.py
@@ -205,6 +205,7 @@ def _build_tree(self) -> None:
                 "Feature File": "file-formats.md#feature-file",
             },
             "Choosing a Classifier": "classifier-types.md",
+            "Multi-Class Classification (Preview)": "multi-class.md",
             "Post-Processing": "postprocessing.md",
             "Features Reference": "features.md",
             "Keyboard Shortcuts Reference": "keyboard-shortcuts.md",
diff --git a/src/jabs/ui/main_control_widget/label_count_widget.py b/src/jabs/ui/main_control_widget/label_count_widget.py
index 9cf6fc8d..992d8da2 100644
--- a/src/jabs/ui/main_control_widget/label_count_widget.py
+++ b/src/jabs/ui/main_control_widget/label_count_widget.py
@@ -47,6 +47,16 @@ def __init__(self, *args, **kwargs):
         frame_header = QtWidgets.QLabel("Frames")
         bout_header = QtWidgets.QLabel("Bouts")
 
+        # Row-header labels for the positive ("Behavior") and negative
+        # ("Not Behavior") classes. Kept as instance attributes so the text can
+        # be retitled per classifier mode (e.g. the selected behavior name and
+        # "None" in multi-class mode); see set_class_labels().
+        self._positive_row_labels = [QtWidgets.QLabel("Behavior"), QtWidgets.QLabel("Behavior")]
+        self._negative_row_labels = [
+            QtWidgets.QLabel("Not Behavior"),
+            QtWidgets.QLabel("Not Behavior"),
+        ]
+
         layout = QtWidgets.QGridLayout()
         layout.setSpacing(2)
         layout.setContentsMargins(0, 0, 0, 0)
@@ -55,13 +65,13 @@ def __init__(self, *args, **kwargs):
         layout.addWidget(frame_header, 0, 0, 1, 3, alignment=Qt.AlignmentFlag.AlignCenter)
         layout.addWidget(QtWidgets.QLabel("Subject"), 1, 1, alignment=Qt.AlignmentFlag.AlignRight)
         layout.addWidget(QtWidgets.QLabel("Total"), 1, 2, alignment=Qt.AlignmentFlag.AlignRight)
-        layout.addWidget(QtWidgets.QLabel("Behavior"), 2, 0)
-        layout.addWidget(QtWidgets.QLabel("Not Behavior"), 3, 0)
+        layout.addWidget(self._positive_row_labels[0], 2, 0)
+        layout.addWidget(self._negative_row_labels[0], 3, 0)
         layout.addWidget(bout_header, 4, 0, 1, 3, alignment=Qt.AlignmentFlag.AlignCenter)
         layout.addWidget(QtWidgets.QLabel("Subject"), 5, 1, alignment=Qt.AlignmentFlag.AlignRight)
         layout.addWidget(QtWidgets.QLabel("Total"), 5, 2, alignment=Qt.AlignmentFlag.AlignRight)
-        layout.addWidget(QtWidgets.QLabel("Behavior"), 6, 0)
-        layout.addWidget(QtWidgets.QLabel("Not Behavior"), 7, 0)
+        layout.addWidget(self._positive_row_labels[1], 6, 0)
+        layout.addWidget(self._negative_row_labels[1], 7, 0)
 
         # add labels containing counts to grid
         layout.addWidget(
@@ -115,6 +125,21 @@ def __init__(self, *args, **kwargs):
 
         self.setLayout(layout)
 
+    def set_class_labels(self, positive_label: str, negative_label: str) -> None:
+        """Retitle the positive/negative row headers.
+
+        Binary mode uses "Behavior"/"Not Behavior"; multi-class mode uses the
+        selected behavior name and the reserved background class name ("None").
+
+        Args:
+            positive_label: text for the behavior (positive) rows.
+            negative_label: text for the not-behavior (negative) rows.
+        """
+        for label in self._positive_row_labels:
+            label.setText(positive_label)
+        for label in self._negative_row_labels:
+            label.setText(negative_label)
+
     def set_counts(
         self,
         frame_behavior_current,
diff --git a/src/jabs/ui/main_control_widget/main_control_widget.py b/src/jabs/ui/main_control_widget/main_control_widget.py
index 2d992de6..cf093023 100644
--- a/src/jabs/ui/main_control_widget/main_control_widget.py
+++ b/src/jabs/ui/main_control_widget/main_control_widget.py
@@ -408,6 +408,10 @@ def set_classifier_selection(self, classifier_type):
             # unable to use the classifier
             pass
 
+    def set_label_summary_class_labels(self, positive_label: str, negative_label: str) -> None:
+        """retitle the label summary's positive/negative row headers"""
+        self._frame_counts.set_class_labels(positive_label, negative_label)
+
     def set_frame_counts(
         self,
         label_behavior_current,
diff --git a/src/jabs/ui/main_window/central_widget.py b/src/jabs/ui/main_window/central_widget.py
index ec2c0801..07eefcb0 100644
--- a/src/jabs/ui/main_window/central_widget.py
+++ b/src/jabs/ui/main_window/central_widget.py
@@ -155,6 +155,9 @@ def __init__(self, *args, **kwargs) -> None:
         self._progress_dialog = None
 
         self._counts = None
+        # project-wide counts for the reserved "None" background track, used to
+        # source the negative-class row of the label summary in multi-class mode
+        self._none_counts = None
         self._bouts_behavior = 0
         self._bouts_not_behavior = 0
 
@@ -355,6 +358,11 @@ def set_project(self, project: Project) -> None:
         self._labels = None
         self._loaded_video = None
 
+        # The reserved "None"-track counts are behavior-independent, so they are
+        # cached across behavior changes and only invalidated when the project
+        # changes (they belong to the previous project here).
+        self._none_counts = None
+
         self._controls.update_project_settings(project.settings)
         self._controls.set_classifier_mode(project.settings_manager.classifier_mode)
         self._search_bar_widget.update_project(project)
@@ -1394,11 +1402,24 @@ def _update_label_counts(self) -> None:
         if self._loaded_video is None:
             return
 
+        multiclass = self._project.settings_manager.classifier_mode == ClassifierMode.MULTICLASS
+
         # update counts for the current video
         self._counts[self._loaded_video.name] = self._project.load_counts(
             self._loaded_video.name, self.behavior
         )
 
+        # In multi-class mode the negative class shown in the label summary is
+        # the reserved "None" background track (explicit negatives are stored
+        # there), not the selected behavior's NOT_BEHAVIOR labels. Load and
+        # refresh those counts in parallel with the behavior counts.
+        if multiclass:
+            if self._none_counts is None:
+                self._none_counts = self._project.counts(MULTICLASS_NONE_BEHAVIOR)
+            self._none_counts[self._loaded_video.name] = self._project.load_counts(
+                self._loaded_video.name, MULTICLASS_NONE_BEHAVIOR
+            )
+
         current_identity = self._controls.current_identity_index
 
         label_behavior_current = 0
@@ -1411,17 +1432,42 @@ def _update_label_counts(self) -> None:
         bout_not_behavior_project = 0
 
         for video, video_counts in self._counts.items():
+            none_video_counts = self._none_counts.get(video, {}) if multiclass else {}
             for identity, counts in video_counts.items():
-                label_behavior_project += counts["unfragmented_frame_counts"][0]
-                label_not_behavior_project += counts["unfragmented_frame_counts"][1]
-                bout_behavior_project += counts["unfragmented_bout_counts"][0]
-                bout_not_behavior_project += counts["unfragmented_bout_counts"][1]
+                behavior_frames = counts["unfragmented_frame_counts"][0]
+                behavior_bouts = counts["unfragmented_bout_counts"][0]
+
+                if multiclass:
+                    # negative class = BEHAVIOR labels on the "None" track
+                    none_counts = none_video_counts.get(identity)
+                    negative_frames = (
+                        none_counts["unfragmented_frame_counts"][0] if none_counts else 0
+                    )
+                    negative_bouts = (
+                        none_counts["unfragmented_bout_counts"][0] if none_counts else 0
+                    )
+                else:
+                    # negative class = NOT_BEHAVIOR labels on the selected behavior
+                    negative_frames = counts["unfragmented_frame_counts"][1]
+                    negative_bouts = counts["unfragmented_bout_counts"][1]
+
+                label_behavior_project += behavior_frames
+                label_not_behavior_project += negative_frames
+                bout_behavior_project += behavior_bouts
+                bout_not_behavior_project += negative_bouts
 
                 if video == self._loaded_video.name and identity == current_identity:
-                    label_behavior_current = counts["unfragmented_frame_counts"][0]
-                    label_not_behavior_current = counts["unfragmented_frame_counts"][1]
-                    bout_behavior_current = counts["unfragmented_bout_counts"][0]
-                    bout_not_behavior_current = counts["unfragmented_bout_counts"][1]
+                    label_behavior_current = behavior_frames
+                    label_not_behavior_current = negative_frames
+                    bout_behavior_current = behavior_bouts
+                    bout_not_behavior_current = negative_bouts
+
+        # retitle the summary rows: behavior name / "None" in multi-class mode,
+        # the standard "Behavior" / "Not Behavior" otherwise
+        if multiclass:
+            self._controls.set_label_summary_class_labels(self.behavior, MULTICLASS_NONE_BEHAVIOR)
+        else:
+            self._controls.set_label_summary_class_labels("Behavior", "Not Behavior")
 
         self._controls.set_frame_counts(
             label_behavior_current,
diff --git a/tests/ui/test_label_count_widget.py b/tests/ui/test_label_count_widget.py
new file mode 100644
index 00000000..c64cc656
--- /dev/null
+++ b/tests/ui/test_label_count_widget.py
@@ -0,0 +1,61 @@
+import pytest
+
+try:
+    from PySide6.QtWidgets import QApplication
+
+    from jabs.ui.main_control_widget.label_count_widget import FrameLabelCountWidget
+
+    SKIP_UI_TESTS = False
+    SKIP_REASON = None
+except ImportError as e:
+    SKIP_UI_TESTS = True
+    SKIP_REASON = f"Qt/UI dependencies not available: {e}"
+
+pytestmark = pytest.mark.skipif(
+    SKIP_UI_TESTS,
+    reason=SKIP_REASON if SKIP_UI_TESTS else "",
+)
+
+
+@pytest.fixture(scope="module", autouse=True)
+def qapp():
+    """Ensure a QApplication exists for widget tests."""
+    app = QApplication.instance()
+    if app is None:
+        app = QApplication([])
+    yield app
+
+
+def test_default_class_labels() -> None:
+    """The summary defaults to the binary-mode row headers."""
+    widget = FrameLabelCountWidget()
+
+    assert [lbl.text() for lbl in widget._positive_row_labels] == ["Behavior", "Behavior"]
+    assert [lbl.text() for lbl in widget._negative_row_labels] == [
+        "Not Behavior",
+        "Not Behavior",
+    ]
+
+
+def test_set_class_labels_retitles_both_rows() -> None:
+    """set_class_labels updates the frame and bout row headers for both classes."""
+    widget = FrameLabelCountWidget()
+
+    widget.set_class_labels("Walk", "None")
+
+    assert [lbl.text() for lbl in widget._positive_row_labels] == ["Walk", "Walk"]
+    assert [lbl.text() for lbl in widget._negative_row_labels] == ["None", "None"]
+
+
+def test_set_class_labels_can_restore_defaults() -> None:
+    """Switching back to binary wording restores the standard headers."""
+    widget = FrameLabelCountWidget()
+
+    widget.set_class_labels("Walk", "None")
+    widget.set_class_labels("Behavior", "Not Behavior")
+
+    assert [lbl.text() for lbl in widget._positive_row_labels] == ["Behavior", "Behavior"]
+    assert [lbl.text() for lbl in widget._negative_row_labels] == [
+        "Not Behavior",
+        "Not Behavior",
+    ]