sgl-project/sglang · error · ValueError

Unsupported LTX-2.3 encoder block: {block_name}

Error message

Unsupported LTX-2.3 encoder block: {block_name}

What it means

_make_ltx23_encoder_block maps known LTX-2.3 encoder block names (stride_map keys such as compress_none, compress_space_res, compress_time_res, compress_all_res variants) to downsampler strides. An unknown block_name in the config yields None from the dict lookup and raises this ValueError.

Source

Thrown at python/sglang/multimodal_gen/runtime/models/vaes/ltx_2_3_condition_encoder.py:103

    if block_name == "res_x":
        return (
            LTX23VideoResBlockStack(
                channels=in_channels,
                num_layers=int(block_config["num_layers"]),
                spatial_padding_mode=spatial_padding_mode,
            ),
            in_channels,
        )

    multiplier = int(block_config.get("multiplier", 2))
    stride_map = {
        "compress_space_res": (1, 2, 2),
        "compress_time_res": (2, 1, 1),
        "compress_all_res": (2, 2, 2),
    }
    stride = stride_map.get(block_name)
    if stride is None:
        raise ValueError(f"Unsupported LTX-2.3 encoder block: {block_name}")
    out_channels = in_channels * multiplier
    return (
        LTXVideoDownsampler3d(
            in_channels=in_channels,
            out_channels=out_channels,
            stride=stride,
            spatial_padding_mode=spatial_padding_mode,
        ),
        out_channels,
    )


class LTX23VideoConditionEncoder(nn.Module, LayerwiseOffloadableModuleMixin):
    layerwise_offload_dit_group_enabled = False
    layer_names = ["down_blocks"]

    def __init__(self, config: dict[str, Any]) -> None:
        super().__init__()

View on GitHub (pinned to 0132848349)

Solutions

1. Print/inspect stride_map in ltx_2_3_condition_encoder.py and use exactly those block names in block_list
2. Use the config shipped with the official LTX-2.3 checkpoint you are loading
3. If your sglang version is older than the checkpoint format, upgrade sglang so stride_map includes the new block names

Example fix

// before
"block_list": ["compress_none", "compress_spatial_res"]

// after
"block_list": ["compress_none", "compress_space_res"]

from sglang.multimodal_gen.runtime.models.vaes.ltx_2_3_condition_encoder import _make_ltx23_encoder_block  # or replicate stride_map
# validate names against the module's stride_map keys
valid = {'compress_none', 'compress_space_res', 'compress_time_res', 'compress_all_res'}  # inspect actual stride_map in your version
assert set(block_list) <= valid, f'unknown block names: {set(block_list) - valid}'

def is_valid_block_list(blocks: list, valid: set) -> bool:
    return all(b in valid for b in blocks)

When it happens

Trigger: Building the LTX-2.3 condition encoder with a block_list containing a block name not present in stride_map — e.g. typos like 'compress_spatial_res', names from a different LTX version, or blocks introduced by a newer config schema than this code supports.

Common situations: Loading an LTX-2.3 checkpoint from a newer/older release with renamed block identifiers; hand-writing the encoder block list; configs generated by external conversion scripts that emit diffusers-style names.

Related errors

• Unsupported latent_log_var: {latent_log_var}
• Unsupported down_block_type: {down_block_type}
• Unsupported time_compression_ratio: {temporal_compression_ra
• Unsupported up_block_type: {up_block_type}
• Unsupported time_compression_ratio: {time_compression_ratio}

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/bf45a622f9181e27. Report an issue: GitHub.