MongoDB/mdbr-leaf-mt

Content

Introduction
Technical Report
Highlights
Benchmarks
Quickstart
Citation

Introduction

mdbr-leaf-mt is a compact high-performance text embedding model designed for classification, clustering, semantic sentence similarity and summarization tasks.

To enable even greater efficiency, mdbr-leaf-mt supports flexible asymmetric architectures and is robust to vector quantization and MRL truncation.

If you are looking to perform semantic search / information retrieval (e.g. for RAGs), please check out our mdbr-leaf-ir model, which is specifically trained for these tasks.

Note: this model has been developed by the ML team of MongoDB Research. At the time of writing it is not used in any of MongoDB's commercial product or service offerings.

Technical Report

A technical report detailing our proposed LEAF training procedure will be available soon.

Highlights

State-of-the-Art Performance: mdbr-leaf-mt achieves new state-of-the-art results for compact embedding models, ranking #1 on the public MTEB v2 (Eng) benchmark leaderboard for models with ≤30M parameters.
Flexible Architecture Support: mdbr-leaf-mt supports asymmetric retrieval architectures enabling even greater retrieval results. See below for more information.
MRL and Quantization Support: embedding vectors generated by mdbr-leaf-mt compress well when truncated (MRL) and can be stored using more efficient types like int8 and binary. See below for more information.

Benchmark Comparison

The table below shows the scores for mdbr-leaf-mt on the MTEB v2 (English) benchmark, compared to other retrieval models.

mdbr-leaf-mt ranks #1 on this benchmark for models with <30M parameters.

Model	Size	MTEB v2 (Eng)
OpenAI text-embedding-3-large	Unknown	66.43
OpenAI text-embedding-3-small	Unknown	64.56
mdbr-leaf-mt	23M	63.97
gte-small	33M	63.22
snowflake-arctic-embed-s	32M	61.59
e5-small-v2	33M	61.32
granite-embedding-small-english-r2	47M	61.07
all-MiniLM-L6-v2	22M	59.03

Quickstart

Sentence Transformers

from sentence_transformers import SentenceTransformer  
  
# Load the model  
model = SentenceTransformer("MongoDB/mdbr-leaf-mt")  
  
# Example queries and documents  
queries = [
    "What is machine learning?",  
    "How does neural network training work?"  
]  
  
documents = [  
    "Machine learning is a subset of artificial intelligence that focuses on algorithms that can learn from data.",  
    "Neural networks are trained through backpropagation, adjusting weights to minimize prediction errors."  
]  
  
# Encode queries and documents  
query_embeddings = model.encode(queries, prompt_name="query")  
document_embeddings = model.encode(documents)  
  
# Compute similarity scores  
scores = model.similarity(query_embeddings, document_embeddings)  

# Print results
for i, query in enumerate(queries):
    print(f"Query: {query}")
    for j, doc in enumerate(documents):
        print(f" Similarity: {scores[i, j]:.4f} | Document {j}: {doc[:80]}...")

# Query: What is machine learning?
#  Similarity: 0.9063 | Document 0: Machine learning is a subset of ...
#  Similarity: 0.7287 | Document 1: Neural networks are trained ...
# 
# Query: How does neural network training work?
#  Similarity: 0.6725 | Document 0: Machine learning is a subset of ...
#  Similarity: 0.8287 | Document 1: Neural networks are trained ...

Transformers Usage

See here.

Asymmetric Retrieval Setup

mdbr-leaf-mt is aligned to mxbai-embed-large-v1, the model it has been distilled from, making the asymmetric system below possible:

# Use mdbr-leaf-mt for query encoding (real-time, low latency)  
query_model = SentenceTransformer("MongoDB/mdbr-leaf-mt")  
query_embeddings = query_model.encode(queries, prompt_name="query")  

# Use a larger model for document encoding (one-time, at index time)  
doc_model = SentenceTransformer("mixedbread-ai/mxbai-embed-large-v1")  
document_embeddings = doc_model.encode(documents)  
  
# Compute similarities  
scores = query_model.similarity(query_embeddings, document_embeddings)

Retrieval results from asymmetric mode are usually superior to the standard mode above.

MRL Truncation

Embeddings have been trained via MRL and can be truncated for more efficient storage:

from torch.nn import functional as F

query_embeds = model.encode(queries, prompt_name="query", convert_to_tensor=True)
doc_embeds = model.encode(documents, convert_to_tensor=True)

# Truncate and normalize according to MRL
query_embeds = F.normalize(query_embeds[:, :256], dim=-1)
doc_embeds = F.normalize(doc_embeds[:, :256], dim=-1)

similarities = model.similarity(query_embeds, doc_embeds)

print('After MRL:')
print(f"* Embeddings dimension: {query_embeds.shape[1]}")
print(f"* Similarities:\n\t{similarities}")

# After MRL:
# * Embeddings dimension: 256
# * Similarities:
# 	  tensor([[0.9164, 0.7219],
#             [0.6682, 0.8393]], device='cuda:0')

Vector Quantization

Vector quantization, for example to int8 or binary, can be performed as follows:

Note: For vector quantization to types other than binary, we suggest performing a calibration to determine the optimal ranges, see here. Good initial values are -1.0 and +1.0.

from sentence_transformers.quantization import quantize_embeddings
import torch

query_embeds = model.encode(queries, prompt_name="query")
doc_embeds = model.encode(documents)

# Quantize embeddings to int8 using -1.0 and +1.0
ranges = torch.tensor([[-1.0], [+1.0]]).expand(2, query_embeds.shape[1]).cpu().numpy()
query_embeds = quantize_embeddings(query_embeds, "int8", ranges=ranges)
doc_embeds = quantize_embeddings(doc_embeds, "int8", ranges=ranges)

# Calculate similarities; cast to int64 to avoid under/overflow
similarities = query_embeds.astype(int) @ doc_embeds.astype(int).T

print('After quantization:')
print(f"* Embeddings type: {query_embeds.dtype}")
print(f"* Similarities:\n{similarities}")

# After quantization:
# * Embeddings type: int8
# * Similarities:
#   [[2202032 1422868]
#    [1421197 1845580]]

Evaluation

Please see here.

Citation

If you use this model in your work, please cite:

@article{mdb_leaf,  
  title         = {LEAF: Lightweight Embedding Alignment Knowledge Distillation Framework},  
  author        = {Robin Vujanic and Thomas Rueckstiess},  
  year          = {2025}
  eprint        = {TBD},
  archiveprefix = {arXiv},
  primaryclass  = {FILL HERE},
  url           = {FILL HERE}
}

License

This model is released under Apache 2.0 License.

Contact

For questions or issues, please open an issue or pull request. You can also contact the MongoDB ML Research team at [email protected].