README.md

---
license: apache-2.0  
base_model: microsoft/MiniLM-L6-v2  
tags:  
- transformers
- sentence-transformers
- sentence-similarity
- feature-extraction
- text-embeddings-inference
- information-retrieval
- knowledge-distillation
- transformers.js
language:
- en
---
<div style="display: flex; justify-content: center;">      
    <div style="display: flex; align-items: center; gap: 10px;">      
        <img src="logo.webp" alt="MongoDB Logo" style="height: 36px; width: auto; border-radius: 4px;">      
        <span style="font-size: 32px; font-weight: bold">MongoDB/mdbr-leaf-mt</span>      
    </div>      
</div>  

# Content

1. [Introduction](#introduction)
2. [Technical Report](#technical-report)
3. [Highlights](#highlights)
4. [Benchmarks](#benchmark-comparison)
5. [Quickstart](#quickstart)
6. [Citation](#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](#asymmetric-retrieval-setup) and is robust to [vector quantization](#vector-quantization) and [MRL truncation](#mrl-truncation).

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

> [!Note]  
> **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 is [available here](https://arxiv.org/abs/2509.12539).

# 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](https://huggingface.co/spaces/mteb/leaderboard) for models with ≤30M parameters.
* **Flexible Architecture Support**: `mdbr-leaf-mt` supports asymmetric retrieval architectures enabling even greater retrieval results. [See below](#asymmetric-retrieval-setup) 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](#mrl-truncation) 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  
  
```python  
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]}...")
```

<details>

<summary>See example output</summary>

```
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 ...
```
</details>

## Transformers.js

If you haven't already, you can install the [Transformers.js](https://huggingface.co/docs/transformers.js) JavaScript library from [NPM](https://www.npmjs.com/package/@huggingface/transformers) using:
```bash
npm i @huggingface/transformers
```

You can then use the model to compute embeddings like this:

```js
import { AutoModel, AutoTokenizer, matmul } from "@huggingface/transformers";

// Download from the 🤗 Hub
const model_id = "MongoDB/mdbr-leaf-mt";
const tokenizer = await AutoTokenizer.from_pretrained(model_id);
const model = await AutoModel.from_pretrained(model_id, {
    dtype: "fp32", // Options: "fp32" | "fp16" | "q8" | "q4" | "q4f16"
});

// Prepare queries and documents
const queries = [
    "What is machine learning?",
    "How does neural network training work?",
];
const 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.",
];
const inputs = await tokenizer([
    ...queries.map((x) => "Represent this sentence for searching relevant passages: " + x),
    ...documents,
], { padding: true });

// Generate embeddings
const { sentence_embedding } = await model(inputs);
const normalized_sentence_embedding = sentence_embedding.normalize();

// Compute similarities
const scores = await matmul(
    normalized_sentence_embedding.slice([0, queries.length]),
    normalized_sentence_embedding.slice([queries.length, null]).transpose(1, 0),
);
const scores_list = scores.tolist();

for (let i = 0; i < queries.length; ++i) {
    console.log(`Query: ${queries[i]}`);
    for (let j = 0; j < documents.length; ++j) {
        console.log(` Similarity: ${scores_list[i][j].toFixed(4)} | Document ${j}: ${documents[j]}`);
    }
    console.log();
}
```

<details>

<summary>See example output</summary>

```
Query: What is machine learning?
 Similarity: 0.9063 | Document 0: Machine learning is a subset of artificial intelligence that focuses on algorithms that can learn from data.
 Similarity: 0.7287 | Document 1: Neural networks are trained through backpropagation, adjusting weights to minimize prediction errors.

Query: How does neural network training work?
 Similarity: 0.6725 | Document 0: Machine learning is a subset of artificial intelligence that focuses on algorithms that can learn from data.
 Similarity: 0.8287 | Document 1: Neural networks are trained through backpropagation, adjusting weights to minimize prediction errors.
```
</details>


## Transformers Usage  

See [here](https://huggingface.co/MongoDB/mdbr-leaf-mt/blob/main/transformers_example_mt.ipynb).
  
## Asymmetric Retrieval Setup

> [!Note]
> **Note**: a version of this asymmetric setup, conveniently packaged into a single model, is [available here](https://huggingface.co/MongoDB/mdbr-leaf-mt-asym).

`mdbr-leaf-mt` is *aligned* to [`mxbai-embed-large-v1`](https://huggingface.co/mixedbread-ai/mxbai-embed-large-v1), the model it has been distilled from, making the asymmetric system below possible: 
  
```python  
# 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](#sentence-transformers).

## MRL Truncation

Embeddings have been trained via [MRL](https://arxiv.org/abs/2205.13147) and can be truncated for more efficient storage:
```python
query_embeds = model.encode(queries, prompt_name="query", truncate_dim=256)
doc_embeds = model.encode(documents, truncate_dim=256)

similarities = model.similarity(query_embeds, doc_embeds)

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

<details>

<summary>See example output</summary>

```
After MRL:
* Embeddings dimension: 256
* Similarities:
    tensor([[0.9164, 0.7219],
            [0.6682, 0.8393]], device='cuda:0')
```
</details>

## 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](https://sbert.net/examples/sentence_transformer/applications/embedding-quantization/README.html#scalar-int8-quantization). 
Good initial values are -1.0 and +1.0.
```python
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}")
```

<details>

<summary>See example output</summary>

```
After quantization:
* Embeddings type: int8
* Similarities:
   [[2202032 1422868]
    [1421197 1845580]]
```
</details>

## Evaluation

Please [see here](https://huggingface.co/MongoDB/mdbr-leaf-mt/blob/main/evaluate_models.ipynb).

# Citation  
  
If you use this model in your work, please cite:  
  
```bibtex  
@misc{mdbr_leaf,
      title={LEAF: Knowledge Distillation of Text Embedding Models with Teacher-Aligned Representations}, 
      author={Robin Vujanic and Thomas Rueckstiess},
      year={2025},
      eprint={2509.12539},
      archivePrefix={arXiv},
      primaryClass={cs.IR},
      url={https://arxiv.org/abs/2509.12539}, 
}
```  
  
# 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].