BOOM_4B_v1

Model Overview

Model Type: Text Embedding
Number of Parameters: 4B
Context Length: 32k
Adapted from Qwen/Qwen3-4B
Pooling: Last token

<div align="center"> <h1> Robust Training for General Text Embeddings via Bagging-Based Model Merging </h1> </div> <p align="center"> 📖 <a href="https://arxiv.org/abs/2602.05787"><strong>arXiv Paper</strong></a> | 🤗 <a href="https://huggingface.co/hengranZhang/BOOM_4B_eng_data_v1"><strong>Model Trained on English data</strong></a> | 🤗 <a href="https://huggingface.co/ICT-TIME-and-Querit/BOOM_4B_v1"><strong>Model Trained on General data </strong></a> | 🛠️ <a href="https://github.com/hengran/Bagging-Based-Model-Merging"><strong>Github</strong></a> | </p>

General-purpose text embedding models underpin a wide range of NLP and information retrieval applications, and are typically trained on large-scale multi-task corpora to encourage broad generalization. Current batch-level shuffling for multi-task text embedding exhibits two practical limitations: suboptimal out-of-domain (OOD) generalization and poor suitability for incremental learning due to expensive full retraining. To address these issues, we propose Bagging-based rObust mOdel Merging (BOOM), which trains multiple embedding models on sampled subsets and merges them into a single model, improving robustness while retaining single-model inference efficiency. Moreover, BOOM naturally supports efficient incremental updates by training lightweight update models on new data with a small historical subset and merging them into the existing model. Experiments across diverse embedding benchmarks demonstrate that BOOM consistently improves both in-domain and OOD performance over full-corpus batch-level shuffling, while substantially reducing training cost in incremental learning settings.

Training data:

General-Text-Data:

• Retrieval: ELI5, HotpotQA, FEVER, MSMARCO, passage and document ranking, NQ, NLI, SQuAD, TriviaQA, and FiQA.
• Reranking: StackOverFlowDupQuestions.
• Classification: AmazonReviews-Classification, Banking77Classification, Emotion-Classification, MTOPIntentClassification, IMDB-Classification, ToxicConversationsClassification, TweetSentimentExtraction-Classification, AmazonCounterfactual-Classification.
• Clustering: Arxiv/Biorxiv/Medrxiv/Reddit/StackExchangeClustering-S2S/P2P, TwentyNewsgroups-Clustering.
• SemanticTextSimilarity(STS):STS12,STS22,STSBenchmark.
• DuReader,MIRACL,Mr.TyDi,andT2-Ranking
• Cornstack: JavaScript, Java, Python,PHP,and Ruby, sampled 500K
  About 2.8M data.

Models Merged

The following models were included in the merge:

• Data_mixing_sampled80_full
• Data_mixingsampled100_full
• Data_mixing_sampled60_full
• Data_mixing_sampled20_full
• Data_mixing_sampled40_full

models:
  - model: Data_mixing_sampled60_full
    parameters:
      weight: 0.6
  - model: Data_mixing_sampled20_full
    parameters:
      weight: 0.2
  - model: Data_mixing_sampled40_full
    parameters:
      weight: 0.4
  - model: Data_mixing_sampled80_full
    parameters:
      weight: 0.8
  - model: Data_mixingsampled100_full
    parameters:
      weight: 1.0
merge_method: multislerp
dtype: float32

This model was merged using the Multi-SLERP merge method.

Usage

Sentence Transformers Usage

# Requires transformers>=4.51.0
# Requires sentence-transformers>=2.7.0

from sentence_transformers import SentenceTransformer

# Load the model
model = SentenceTransformer("ICT-TIME-and-Querit/BOOM_4B_v1")

# We recommend enabling flash_attention_2 for better acceleration and memory saving,
# together with setting `padding_side` to "left":
# model = SentenceTransformer(
#     "Qwen/Qwen3-Embedding-4B",
#     model_kwargs={"attn_implementation": "flash_attention_2", "device_map": "auto"},
#     tokenizer_kwargs={"padding_side": "left"},
# )

# The queries and documents to embed
queries = [
    "What is the capital of China?",
    "Explain gravity",
]
documents = [
    "The capital of China is Beijing.",
    "Gravity is a force that attracts two bodies towards each other. It gives weight to physical objects and is responsible for the movement of planets around the sun.",
]

# Encode the queries and documents. Note that queries benefit from using a prompt
# Here we use the prompt called "query" stored under `model.prompts`, but you can
# also pass your own prompt via the `prompt` argument
query_embeddings = model.encode(queries, prompt_name="query")
document_embeddings = model.encode(documents)

# Compute the (cosine) similarity between the query and document embeddings
similarity = model.similarity(query_embeddings, document_embeddings)
print(similarity)
# tensor([[0.4402, 0.0335],
        [0.0943, 0.3470]])

Transformers Usage

# Requires transformers>=4.51.0
import torch
import torch.nn.functional as F

from torch import Tensor
from transformers import AutoTokenizer, AutoModel


def last_token_pool(last_hidden_states: Tensor,
                 attention_mask: Tensor) -> Tensor:
    left_padding = (attention_mask[:, -1].sum() == attention_mask.shape[0])
    if left_padding:
        return last_hidden_states[:, -1]
    else:
        sequence_lengths = attention_mask.sum(dim=1) - 1
        batch_size = last_hidden_states.shape[0]
        return last_hidden_states[torch.arange(batch_size, device=last_hidden_states.device), sequence_lengths]


def get_detailed_instruct(task_description: str, query: str) -> str:
    return f'Instruct: {task_description}\nQuery:{query}'

# Each query must come with a one-sentence instruction that describes the task
task = 'Given a web search query, retrieve relevant passages that answer the query'

queries = [
    get_detailed_instruct(task, 'What is the capital of China?'),
    get_detailed_instruct(task, 'Explain gravity')
]
# No need to add instruction for retrieval documents
documents = [
    "The capital of China is Beijing.",
    "Gravity is a force that attracts two bodies towards each other. It gives weight to physical objects and is responsible for the movement of planets around the sun."
]
input_texts = queries + documents

tokenizer = AutoTokenizer.from_pretrained("ICT-TIME-and-Querit/BOOM_4B_v1", padding_side='left')
model = AutoModel.from_pretrained("ICT-TIME-and-Querit/BOOM_4B_v1")

# We recommend enabling flash_attention_2 for better acceleration and memory saving.
# model = AutoModel.from_pretrained("ICT-TIME-and-Querit/BOOM_4B_v1", attn_implementation="flash_attention_2", torch_dtype=torch.float16).cuda()

max_length = 8192

# Tokenize the input texts
batch_dict = tokenizer(
    input_texts,
    padding=True,
    truncation=True,
    max_length=max_length,
    return_tensors="pt",
)
batch_dict.to(model.device)
outputs = model(**batch_dict)
embeddings = last_token_pool(outputs.last_hidden_state, batch_dict['attention_mask'])

# normalize embeddings
embeddings = F.normalize(embeddings, p=2, dim=1)
scores = (embeddings[:2] @ embeddings[2:].T)
print(scores.tolist())
# [[0.4401702880859375, 0.03349032998085022], [0.09427911043167114, 0.34699785709381104]]

Evaluation

MTEB (Multilingual)

Citation

If you find our work helpful, feel free to give us a cite.

@article{zhang2026bagging,
  title={Bagging-Based Model Merging for Robust General Text Embeddings},
  author={Zhang, Hengran and Bi, Keping and Guo, Jiafeng and Zhang, Jiaming and Yang, Wenbo and Shi, Daiting and Cheng, Xueqi},
  journal={arXiv preprint arXiv:2602.05787},
  year={2026}
}