sgl-project/sglang · error · ValueError

Unsupported Mobius layer type: {checkpoint_type}

Error message

Unsupported Mobius layer type: {checkpoint_type}

What it means

The layer factory only recognizes a fixed set of Mobius layer types (the branches above, ending in linear_attn). Any other checkpoint_type string falls through to this generic ValueError.

Source

Thrown at python/sglang/srt/models/interns2_mobius.py:747

        def get_layer(idx: int, prefix: str):
            checkpoint_type = config.layer_types[idx]
            if checkpoint_type == "full_attention":
                return InternS2MobiusAttentionDecoderLayer(
                    config=config,
                    layer_id=idx,
                    quant_config=quant_config,
                    prefix=add_prefix("self_attn", prefix),
                    alt_stream=alt_stream,
                )
            if checkpoint_type == "linear_attention":
                return InternS2MobiusLinearDecoderLayer(
                    config=config,
                    layer_id=idx,
                    quant_config=quant_config,
                    prefix=add_prefix("linear_attn", prefix),
                    alt_stream=alt_stream,
                )
            raise ValueError(f"Unsupported Mobius layer type: {checkpoint_type}")

        self.layers, self._start_layer, self._end_layer = make_layers(
            config.num_hidden_layers,
            get_layer,
            pp_rank=0,
            pp_size=1,
            prefix=f"{prefix}.layers",
        )
        self.norm = GemmaRMSNorm(config.hidden_size, eps=config.rms_norm_eps)
        self.layers_to_capture = []

    def get_hidden_dim(self, module_name: str, layer_idx: int):
        if module_name == "gate_up_proj":
            return (
                self.config.hidden_size,
                self.config.shared_expert_intermediate_size * 2,
            )
        if module_name == "down_proj":

View on GitHub (pinned to 0132848349)

Solutions

1. Print checkpoint_type in the factory to see the actual string
2. Map the new type string to the closest supported layer in your config
3. Update the model implementation to handle the new layer type

Example fix

# before
if checkpoint_type == "linear_attn": ...
raise ValueError(...)

# after
if checkpoint_type in ("linear_attn", "gated_delta_net"):
    return _InternS2MobiusLinearAttn(...)

SUPPORTED = {"full_attn", "linear_attn"}  # per factory branches
assert checkpoint_type in SUPPORTED, f"unsupported layer type {checkpoint_type}"

def is_supported_layer(t: str) -> bool:
    return t in {"full_attn", "linear_attn"}

try:
    layer = get_layer(idx, checkpoint_type)
except ValueError as e:
    if "Unsupported Mobius layer type" in str(e):
        raise RuntimeError(f"convert checkpoint: {e}")
    raise

When it happens

Trigger: config/checkpoint layer type strings not matching the supported set (e.g., a new 'mamba2' or renamed 'gated_delta' variant), causing no branch of get_layer to return before the fallthrough.

Common situations: Loading checkpoints from a newer/older Intern-S2-Mobius release with renamed layer types, or hand-edited configs.

Related errors

• Helion KDA decode requires power-of-two key and value head d
• `A_log` must have {HV} elements (got {A_log.numel()}).
• `dt_bias` must have {HV * K} elements (got {dt_bias.numel()}
• Activation function {act_fn_name!r} is not supported.
• Expected hidden_size to be {self.hidden_size}, but found: {h

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/b770efe810985431. Report an issue: GitHub.