KaLM-Reranker-V1: Fast but Not Late Interaction for Compressed Document Reranking

We present KaLM-Reranker-V1, a fast but not late-interaction (FBNL) reranker that decouples query and passage computation while retaining expressive relevance modeling.

Built on an encoder-decoder architecture, KaLM-Reranker-V1 uses the encoder to pre-encode passages with Matryoshka embedding pooling, while the decoder models the system instruction, user instruction, and query intent; cross-attention then captures relevance between the query context and passage representations. This design makes KaLM-Reranker-V1 efficient through decoupled passage encoding, yet not late interaction, by preserving rich relevance modeling through cross-attention.

We instantiate KaLM-Reranker-V1 in three sizes, Nano, Small, and Large, with 0.27B, 1B, and 4B activated parameters, respectively.

Extensive experiments on BEIR, MIRACL, and LMEB show that the KaLM-Reranker-V1 series achieves competitive reranking performance compared with strong industrial rerankers while significantly reducing online overhead.

Model Details

Models	Activated Params.	Non-Embedding Params.	Embedding Params.	#Layers	Sequence Length	Document Token Dim.	MEP Support	Instruction Aware
KaLM-Reranker-V1-Nano	0.27B	100M	168M	18	128K	640	1x-32x	Yes
KaLM-Reranker-V1-Small	1B	698M	302M	26	128K	1152	1x-32x	Yes
KaLM-Reranker-V1-Large	4B	3209M	675M	34	128K	2560	1x-32x	Yes

Prompt Template

 f"<Document>: {document}"

(
    f"<bos><start_of_turn>user\n"
    f"Judge whether the Document meets the requirements based on the Query and the Instruct provided. Note that the answer can only be \"yes\" or \"no\".\n\n"
    f"<Instruct>: {task_instruction}\n"
    f"<Query>: {query}<end_of_turn>\n"
    f"<start_of_turn>model\n\n\n\n"
)

Evaluation

BEIR

On BEIR, KaLM-Reranker-V1 achieves state-of-the-art performance, on par with strong industrial models such as the Qwen3-Reranker series.

MIRACL

On MIRACL, despite not being extensively trained on multilingual data, KaLM-Reranker-V1 still shows excellent reranking performance.

LMEB

On LMEB, reranking models demonstrate a clear advantage, with even the 0.27B Nano model remaining competitive with 7–12B embedding models.

Usage

import argparse
from typing import Optional


def optional_positive_int(value: str) -> Optional[int]:
    if value.lower() == "none":
        return None
    try:
        parsed = int(value)
    except ValueError as error:
        raise argparse.ArgumentTypeError(
            "must be a positive integer or 'none'"
        ) from error
    if parsed <= 0:
        raise argparse.ArgumentTypeError("must be a positive integer or 'none'")
    return parsed


def build_parser() -> argparse.ArgumentParser:
    parser = argparse.ArgumentParser(
        formatter_class=argparse.ArgumentDefaultsHelpFormatter,
    )
    parser.add_argument(
        "--model",
        default="KaLM-Embedding/KaLM-Reranker-V1-Small",
        help="Hugging Face model ID or local checkpoint path.",
    )
    parser.add_argument(
        "--device",
        default=None,
        help="Inference device, such as 'cuda', 'cuda:0', or 'cpu'.",
    )
    parser.add_argument(
        "--dtype",
        default=None,
        choices=("bfloat16", "bf16", "float16", "fp16", "float32", "fp32"),
        help="Model parameter dtype. By default, use BF16 on CUDA and FP32 on CPU.",
    )
    parser.add_argument(
        "--batch-size",
        type=int,
        default=32,
        help="Number of query-document pairs scored per inference batch.",
    )
    parser.add_argument(
        "--query-max-length",
        type=int,
        default=512,
        help=(
            "Maximum tokens in the raw query before it is inserted into the "
            "decoder prompt; prompt tokens are not included in this limit."
        ),
    )
    parser.add_argument(
        "--reranker-max-length",
        type=int,
        default=1024,
        help=(
            "Maximum encoder tokens for '<Document>: {passage}'. This is not a "
            "combined query-document context limit."
        ),
    )
    parser.add_argument(
        "--chunk-size",
        type=optional_positive_int,
        default=4,
        metavar="N|none",
        help=(
            "Number of encoder token hidden states per mean-pooled chunk; use "
            "'none' to disable encoder chunk pooling."
        ),
    )
    return parser


def main() -> None:
    args = build_parser().parse_args()

    from kalm_reranker import KaLMReranker

    reranker = KaLMReranker(
        args.model,
        device=args.device,
        dtype=args.dtype,
        batch_size=args.batch_size,
        query_max_length=args.query_max_length,
        max_length=args.reranker_max_length,
        chunk_size=args.chunk_size,
    )
    query = "What is the capital of China?"
    documents = [
        "The capital of China is Beijing.",
        "Gravity attracts bodies toward one another.",
    ]
    instruction = "Given a query, retrieve documents that answer the query."

    pairs = [(query, document) for document in documents]
    print("scores:", reranker.predict(pairs, instruction=instruction))
    print("rankings:", reranker.rank(query, documents, instruction=instruction))
    

if __name__ == "__main__":
    main()

'''
scores: [0.9999822378158569, 3.187565198459197e-06]
rankings: [{'corpus_id': 0, 'score': 0.9999822378158569}, {'corpus_id': 1, 'score': 3.187565198459197e-06}]
'''

Citation

If you find this model useful, please consider citing our papers.

@misc{zhao2026kalmrerankerv1,
      title={KaLM-Reranker-V1: Fast but Not Late Interaction for Compressed Document Reranking}, 
      author={Xinping Zhao and Jiaxin Xu and Ziqi Dai and Xin Zhang and Shouzheng Huang and Danyu Tang and Xinshuo Hu and Meishan Zhang and Baotian Hu and Min Zhang},
      year={2026},
      eprint={2606.22807},
      archivePrefix={arXiv},
      primaryClass={cs.CL},
      url={https://arxiv.org/abs/2606.22807}, 
}

@inproceedings{zhao2026kalmembeddingv2,
      title={KaLM-Embedding-V2: Superior Training Techniques and Data Inspire A Versatile Embedding Model},
      author={Xinping Zhao and Xinshuo Hu and Zifei Shan and Shouzheng Huang and Yao Zhou and Xin Zhang and Zetian Sun and Zhenyu Liu and Dongfang Li and Xinyuan Wei and Youcheng Pan and Yang Xiang and Meishan Zhang and Haofen Wang and Jun Yu and Baotian Hu and Min Zhang},
      booktitle={The Fourteenth International Conference on Learning Representations},
      year={2026},
      url={https://openreview.net/forum?id=Y7qzhvWhcz}
}

@misc{hu2025kalmembedding,
      title={KaLM-Embedding: Superior Training Data Brings A Stronger Embedding Model}, 
      author={Xinshuo Hu and Zifei Shan and Xinping Zhao and Zetian Sun and Zhenyu Liu and Dongfang Li and Shaolin Ye and Xinyuan Wei and Qian Chen and Baotian Hu and Haofen Wang and Jun Yu and Min Zhang},
      year={2025},
      eprint={2501.01028},
      archivePrefix={arXiv},
      primaryClass={cs.CL},
      url={https://arxiv.org/abs/2501.01028}, 
}