keras-team/keras · error · ValueError

Flash attention is not supported in numpy backend.

Error message

Flash attention is not supported in numpy backend.

What it means

Error "Flash attention is not supported in numpy backend." thrown in keras-team/keras.

Source

Thrown at keras/src/backend/numpy/ops/nn.py:1427

    encoded = encoded.astype(encoded_dtype)
    return encoded


def dot_product_attention(
    query,
    key,
    value,
    bias=None,
    mask=None,
    scale=None,
    is_causal=False,
    flash_attention=None,
    attn_logits_soft_cap=None,
):
    if flash_attention is None:
        flash_attention = False
    if flash_attention:
        raise ValueError("Flash attention is not supported in numpy backend.")

    # Ref: jax.nn.dot_product_attention
    # https://github.com/jax-ml/jax/blob/jax-v0.4.32/jax/_src/nn/functions.py#L828
    # Not support `query_seq_lengths` and `key_value_seq_lengths` args
    query = convert_to_tensor(query)
    key = convert_to_tensor(key)
    value = convert_to_tensor(value)
    if len(query.shape) != 4:
        raise ValueError(
            "`dot_product_attention` only supports 4D inputs. "
            f"Received: query.shape={query.shape}, key.shape={key.shape}, "
            f"value.shape={value.shape}."
        )
    compute_dtype = backend.result_type(query.dtype, key.dtype, value.dtype)
    query = cast(query, compute_dtype)
    key = cast(key, compute_dtype)
    value = cast(value, compute_dtype)
    if bias is not None:

View on GitHub (pinned to 7a34a03db6)

When it happens

Trigger: Thrown at keras/src/backend/numpy/ops/nn.py:1427 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/db1f6d1df8d25915. Report an issue: GitHub.