huggingface/transformers · error · RuntimeError

No hyperparameter search backend available.\n - To install {

Error message

No hyperparameter search backend available.\n - To install {backend.name} run {backend.pip_install()}

What it means

Error "No hyperparameter search backend available.\n - To install {backend.name} run {backend.pip_install()}" thrown in huggingface/transformers.

Source

Thrown at src/transformers/hyperparameter_search.py:117

    def default_hp_space(self, trial):
        return default_hp_space_wandb(trial)


ALL_HYPERPARAMETER_SEARCH_BACKENDS = {
    HPSearchBackend(backend.name): backend for backend in [OptunaBackend, RayTuneBackend, WandbBackend]
}


def default_hp_search_backend() -> str:
    available_backends = [backend for backend in ALL_HYPERPARAMETER_SEARCH_BACKENDS.values() if backend.is_available()]
    if len(available_backends) > 0:
        name = available_backends[0].name
        if len(available_backends) > 1:
            logger.info(
                f"{len(available_backends)} hyperparameter search backends available. Using {name} as the default."
            )
        return name
    raise RuntimeError(
        "No hyperparameter search backend available.\n"
        + "\n".join(
            f" - To install {backend.name} run {backend.pip_install()}"
            for backend in ALL_HYPERPARAMETER_SEARCH_BACKENDS.values()
        )
    )

View on GitHub (pinned to a597f97485)

Solutions

1. Install one of the supported HPO backends (e.g. `pip install optuna` or `pip install ray[tune]`).
2. Remove the hyperparameter search call if no backend is desired.

When it happens

Trigger: Raised in default_hp_search_backend when no supported hyperparameter search backend is installed at all.

Common situations: Running hyperparameter_search without installing optuna, ray[tune], sigopt, or wandb.

AI-assisted analysis of huggingface/transformers@a597f97485 (2026-08-14). Data as JSON: /api/errors/1d2c64a7587f715e. Report an issue: GitHub.