Multilingual E5 Small is a multilingual sentence embedding model optimized for semantic search and retrieval tasks. This CoreML version enables on-device inference on Apple platforms.

Key Features

Multilingual: Supports 100+ languages including English, Japanese, Chinese, Korean, German, French, Spanish, and more
Search-optimized: Designed specifically for retrieval tasks
Cross-lingual: Can match queries in one language to documents in another
On-device: Runs locally on iPhone/iPad/Mac without internet

Model Details

Property	Value
Base Model	intfloat/multilingual-e5-small
Embedding Dimensions	384
Max Sequence Length	256 (configurable up to 512)
Model Size	~224 MB
Precision	Float16
Minimum iOS	17.0
Minimum macOS	14.0

Usage

Input Format

E5 models use prefixes to distinguish between queries and documents:

Query: "query: your search query here"
Document: "passage: your document text here"

Swift Example

swift

import CoreML

// Load model
let config = MLModelConfiguration()
config.computeUnits = .cpuAndNeuralEngine
let model = try MLModel(contentsOf: modelURL, configuration: config)

// Prepare inputs (after tokenization)
let inputIds: MLMultiArray = // tokenized input
let attentionMask: MLMultiArray = // attention mask

// Run inference
let input = try MLDictionaryFeatureProvider(dictionary: [
    "input_ids": MLFeatureValue(multiArray: inputIds),
    "attention_mask": MLFeatureValue(multiArray: attentionMask)
])
let output = try model.prediction(from: input)
let embeddings = output.featureValue(for: "embeddings")?.multiArrayValue

Tokenizer

Use the included tokenizer.json with swift-transformers:

swift

import Tokenizers

let tokenizer = try await AutoTokenizer.from(modelFolder: tokenizerURL)
let encoded = tokenizer.encode(text: "query: your text")

Performance

Tested on iOS with Neural Engine:

Device	Inference Time
iPhone 15 Pro	~15ms
iPhone 13	~25ms
M1 Mac	~10ms

Accuracy Comparison

Tested with 10 mixed Japanese/English technical queries:

Model	Accuracy	Avg Score
Apple NLEmbedding	20%	0.558
This Model (E5)	100%	0.860

Files

MultilingualE5Small.mlpackage/ - CoreML model package
tokenizer.json - Tokenizer vocabulary and configuration
tokenizer_config.json - Tokenizer settings

Conversion

Converted using coremltools with FP16 precision:

python

import coremltools as ct

mlmodel = ct.convert(
    traced_model,
    inputs=[
        ct.TensorType(name="input_ids", shape=(1, 256), dtype=np.int32),
        ct.TensorType(name="attention_mask", shape=(1, 256), dtype=np.int32),
    ],
    outputs=[
        ct.TensorType(name="embeddings", dtype=np.float16),
    ],
    convert_to="mlprogram",
    minimum_deployment_target=ct.target.iOS17,
    compute_precision=ct.precision.FLOAT16,
)

License

MIT License (same as the base model)

Citation

bibtex

@article{wang2024multilingual,
  title={Multilingual E5 Text Embeddings: A Technical Report},
  author={Wang, Liang and Yang, Nan and Huang, Xiaolong and Yang, Linjun and Majumder, Rangan and Wei, Furu},
  journal={arXiv preprint arXiv:2402.05672},
  year={2024}
}

Acknowledgments

Original model by intfloat
CoreML conversion for ReadMD iOS app

tamikisg/multilingual-e5-small-coreml

Multilingual E5 Small - CoreML

Model Description