keras-team/keras · error · RuntimeError

Backend '{backend.backend()}' must implement a layer mixin c

Error message

Backend '{backend.backend()}' must implement a layer mixin class.

What it means

Error "Backend '{backend.backend()}' must implement a layer mixin class." thrown in keras-team/keras.

Source

Thrown at keras/src/layers/layer.py:65

from keras.src.ops.operation import Operation
from keras.src.quantizers.quantization_config import validate_and_resolve_config
from keras.src.utils import python_utils
from keras.src.utils import summary_utils
from keras.src.utils import traceback_utils
from keras.src.utils import tracking

if backend.backend() == "tensorflow":
    from keras.src.backend.tensorflow.layer import TFLayer as BackendLayer
elif backend.backend() == "jax":
    from keras.src.backend.jax.layer import JaxLayer as BackendLayer
elif backend.backend() == "torch":
    from keras.src.backend.torch.layer import TorchLayer as BackendLayer
elif backend.backend() == "numpy":
    from keras.src.backend.numpy.layer import NumpyLayer as BackendLayer
elif backend.backend() == "openvino":
    from keras.src.backend.openvino.layer import OpenvinoLayer as BackendLayer
else:
    raise RuntimeError(
        f"Backend '{backend.backend()}' must implement a layer mixin class."
    )


@keras_export(["keras.Layer", "keras.layers.Layer"])
class Layer(BackendLayer, Operation):
    """This is the class from which all layers inherit.

    A layer is a callable object that takes as input one or more tensors and
    that outputs one or more tensors. It involves *computation*, defined
    in the `call()` method, and a *state* (weight variables). State can be
    created:

    * in `__init__()`, for instance via `self.add_weight()`;
    * in the optional `build()` method, which is invoked by the first
      `__call__()` to the layer, and supplies the shape(s) of the input(s),
      which may not have been known at initialization time.

View on GitHub (pinned to 7a34a03db6)

When it happens

Trigger: Thrown at keras/src/layers/layer.py:65 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of keras-team/keras@7a34a03db6 (2026-08-25). Data as JSON: /api/errors/bcdb4d0784107e09. Report an issue: GitHub.