BerriAI/litellm · error · ValueError

tier_labels values must be non-empty; blank labels for tiers

Error message

tier_labels values must be non-empty; blank labels for tiers: {', '.join(blank)}

What it means

Config validator on ComplexityRouterConfig: some tier_labels entries are blank/whitespace after stripping (tiers listed in the message). Blank labels would render as empty in logs and the classifier rubric.

Source

Thrown at litellm/router_strategy/complexity_router/config.py:665

        return self

    @model_validator(mode="after")
    def _validate_semantic_matching(self) -> "ComplexityRouterConfig":
        if not self.semantic_keyword_matching:
            return self
        if not self.embedding_model:
            raise ValueError("embedding_model is required when semantic_keyword_matching is enabled")
        if not self.keyword_tier_rules:
            raise ValueError("keyword_tier_rules must be non-empty when semantic_keyword_matching is enabled")
        return self

    @model_validator(mode="after")
    def _validate_tier_labels(self) -> "ComplexityRouterConfig":
        if not self.tier_labels:
            return self
        blank: Final = tuple(sorted(tier.value for tier, label in self.tier_labels.items() if not label.strip()))
        if blank:
            raise ValueError(f"tier_labels values must be non-empty; blank labels for tiers: {', '.join(blank)}")
        shadowed: Final = tuple(
            sorted(
                f"{tier.value} -> {label.strip()}"
                for tier, label in self.tier_labels.items()
                if label.strip().upper() in ComplexityTier.__members__ and label.strip().upper() != tier.value
            )
        )
        if shadowed:
            raise ValueError(
                "tier_labels values must not reuse another tier's canonical name, which would make logs "
                f"and the classifier rubric ambiguous: {', '.join(shadowed)}"
            )
        labeled: Final = self.labeled_tiers()
        folded_labels: Final = tuple(label.casefold() for _, label in labeled)
        duplicated: Final = tuple(
            " and ".join(tier.value for tier, label in labeled if label.casefold() == folded)
            for position, folded in enumerate(folded_labels)
            if folded_labels.count(folded) > 1 and folded_labels.index(folded) == position

View on GitHub (pinned to 77b7c6c40c)

Solutions

1. Give every tier a non-empty label in tier_labels.

When it happens

Trigger: Thrown at litellm/router_strategy/complexity_router/config.py:665 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of BerriAI/litellm@77b7c6c40c (2026-08-18). Data as JSON: /api/errors/02c068adc2d4d2ba. Report an issue: GitHub.