multitask

A flexible multi-task learning library for NLP supporting mixed task types (binary/multiclass/multilabel/regression), multiple encoders, and distributed training.

Table of Contents

• Features
• Installation
• Quick Start
• Data Format
• Encoder Types
• Training
• Model Persistence
• Configuration
• Troubleshooting
• API Reference
• Examples
• Citation and License

Features

• Mixed task types in single model (binary, multiclass, multilabel, regression)
• Multiple encoders: TensorFlow Hub, HuggingFace, pre-computed embeddings
• Automatic class imbalance and task weighting
• Automatic threshold optimization for binary/multilabel tasks
• Cross-platform distributed training with automatic GPU detection
• Model persistence with threshold saving
• Comprehensive type hints

Installation

From PyPI

pip install multitask-py

This installs the core library and its dependencies:

• TensorFlow 2.19.x (+ TF Hub, TF Text)
• NumPy
• scikit-learn
• pandas
• PyYAML

To install with all optional backends and features:

pip install 'multitask-py[huggingface,openai,cohere,voyageai,regression]'

Or install extras individually as needed:

Extra	What it adds
huggingface	transformers, torch, huggingface-hub
openai	OpenAI embeddings API client
cohere	Cohere embeddings API client
voyageai	Voyage AI embeddings API client
regression	scipy (Pearson r in evaluation)

From source

git clone https://github.com/yourusername/multitask.git
cd multitask
pip install .                  # core only
pip install '.[huggingface]'   # core + HuggingFace support

GPU support

• Apple Silicon: pip install tensorflow-metal==1.2.0
• NVIDIA: pip install tensorflow[and-cuda]

Note: tensorflow-metal 1.2.0 is compatible with the TF 2.19.x family installed by multitask-py. Do not upgrade TensorFlow to 2.20+ independently — that combination is not supported by any currently available tensorflow-metal release and will produce import errors at runtime.

Developers

The Conda environment pins every dependency for reproducibility:

conda env create -f environment.yml
conda activate multitask
pip install -e .

This includes all optional extras, dev tools (pytest, black, mypy), and system libraries (MPI, BLAS, HDF5) that pip cannot provide.

Package management overview

File	Audience	Purpose
pyproject.toml	Users	Declares runtime deps (loose bounds) and optional extras
environment.yml	Developers	Pins exact versions for a reproducible conda environment

Quick Start

from multitask import ModelConfig, TrainingConfig, MultiTaskModel, Trainer, EncoderConfig
from multitask.config import EncoderIntegration, EncoderInputType

# Configure universal sentence encoder
encoder_config = EncoderConfig(
    encoder_integration=EncoderIntegration.TFHUB,
    encoder_input_type=EncoderInputType.RAW_STRING,
    encoder_identifier='https://tfhub.dev/google/universal-sentence-encoder/4',
)

# Three tasks → task_structure must have three outputs (see docs for hierarchical layouts)
config = ModelConfig(
    task_structure=[[3]],
    task_names=['sentiment', 'toxicity', 'emotions'],
    task_types=['multiclass', 'binary', 'multiclass'],
    num_classes_per_task=[3, 2, 5],  # binary tasks use num_classes=2
    encoder_config=encoder_config,
)

model = MultiTaskModel(config)

# Train: build tf.data.Dataset batches of (inputs, labels_dict); see docs/DATA_FORMAT.md
train_dataset = ...  # e.g. tf.data.Dataset.from_tensor_slices(...) then .batch(...)
val_dataset = ...
trainer = Trainer(model, TrainingConfig())
history, thresholds = trainer.fit(train_dataset, val_dataset, num_tasks=3)

# Predict: pass tensors or numpy matching the model input (e.g. text or embeddings)
predictions = model.predict(x_test)  # dict[str, Tensor] per task

Data Format

Text Input

DataFrame with text column and one column per task:

import pandas as pd

data = pd.DataFrame({
    'text': ['great product', 'terrible', ...],
    'sentiment': [2, 0, ...],              # 0-2 for 3-class
    'toxicity': [0, 1, ...],               # 0-1 for binary
    'emotions': ['joy anger', 'fear', ...],  # Space-separated for multilabel
})

Pre-computed Embeddings

Add embedding column with numpy arrays:

import numpy as np
from multitask.config import EncoderInputType

data['embedding'] = [np.random.randn(768) for _ in range(len(data))]

encoder_config = EncoderConfig(
    encoder_input_type=EncoderInputType.PRECOMPUTED,
    embedding_dim=768
)

# PRECOMPUTED path: no encoder_identifier is required
# (inputs are embedding vectors provided directly by your dataset)

config = ModelConfig(
    task_structure=[[1]],
    task_names=['sentiment'],
    task_types=['multiclass'],
    num_classes_per_task=[3],
    encoder_config=encoder_config
)

Missing Labels

You can set any float as the missing labels. Here we use -1 to mark missing labels (excluded from loss):

data = pd.DataFrame({
    'text': ['text1', 'text2', 'text3'],
    'task1': [0, 1, -1],     # task1 missing for text3
    'task2': [1, -1, 0],     # task2 missing for text2
})

# Optional: use a custom missing-label value globally
config = ModelConfig(
    task_structure=[[2]],
    task_names=['task1', 'task2'],
    task_types=['binary', 'multiclass'],
    num_classes_per_task=[2, 3],
    mask_value=-999.0,
)

See DATA_FORMAT.md for complete documentation.

Encoder Types

TensorFlow Hub

from multitask.config import EncoderIntegration, EncoderInputType

# Universal Sentence Encoder
encoder_config = EncoderConfig(
    encoder_identifier="https://tfhub.dev/google/universal-sentence-encoder/4",
    encoder_input_type=EncoderInputType.RAW_STRING,
    encoder_integration=EncoderIntegration.TFHUB
)

config = ModelConfig(
    task_structure=[[1]],
    task_names=['sentiment'],
    task_types=['multiclass'],
    num_classes_per_task=[3],
    encoder_config=encoder_config
)

HuggingFace

from multitask.config import EncoderIntegration, EncoderInputType

encoder_config = EncoderConfig(
    encoder_identifier="bert-base-uncased",
    encoder_input_type=EncoderInputType.HUGGINGFACE_TOKENS,
    encoder_integration=EncoderIntegration.HUGGINGFACE
)

config = ModelConfig(
    task_structure=[[1]],
    task_names=['sentiment'],
    task_types=['multiclass'],
    num_classes_per_task=[3],
    encoder_config=encoder_config
)

Pre-computed Embeddings

from multitask.config import EncoderInputType

encoder_config = EncoderConfig(
    embedding_dim=768,
    encoder_input_type=EncoderInputType.PRECOMPUTED,
)

config = ModelConfig(
    task_structure=[[1]],
    encoder_config=encoder_config
)

See ENCODER_SUPPORT.md for all options.

Training

Basic

config = TrainingConfig(batch_size=32, epochs=10, learning_rate=2e-5)
trainer = Trainer(model, config)
history, thresholds = trainer.fit(train_dataset, val_dataset, num_tasks=N)

Automatic Weight Computation

By default, trainer automatically computes:

• Task weights: Inversely proportional to non-masked samples per task
• Class weights: Inversely proportional to class frequency

Override with explicit weights:

trainer.fit(
    train_data, val_data,
    class_weights=[{0: 1.0, 1: 2.0}, ...],  # Per task
    task_weights=[1.0, 2.0, ...],
)

Threshold Optimization

Find optimal thresholds for binary/multilabel tasks:

history, thresholds = trainer.fit(
    train_dataset, val_dataset, num_tasks=N,
    optimize_thresholds=True,  # Uses Youden's J statistic
)

Distributed Training

Automatic GPU detection and strategy selection:

from multitask import get_distribution_strategy, setup_gpu_memory_growth

setup_gpu_memory_growth()
strategy, info = get_distribution_strategy('auto', verbose=True)

# Do NOT wrap model/trainer creation in strategy.scope() —
# Trainer.fit() enters the scope internally during compilation.
model = MultiTaskModel(config)
trainer = Trainer(model, training_config, strategy=strategy)

trainer.fit(train_dataset, val_dataset, num_tasks=N)

See DISTRIBUTED_TRAINING.md.

Checkpointing

trainer.fit(
    train_dataset, val_dataset, num_tasks=N,
    checkpoint_dir='checkpoints/exp1',
    checkpoint_monitor='val_loss',
)

Verbosity

trainer.fit(train_dataset, val_dataset, num_tasks=N, verbose=0)  # Silent
trainer.fit(train_dataset, val_dataset, num_tasks=N, verbose=1)  # Progress (default)
trainer.fit(train_dataset, val_dataset, num_tasks=N, verbose=2)  # One line per epoch

Model Persistence

Save

model.save('models/my_model', thresholds=thresholds)

Load

from multitask import load_model

model, thresholds = load_model('models/my_model')
predictions = model.predict(x_test)

See MODEL_PERSISTENCE.md.

Configuration

ModelConfig

ModelConfig(
    task_structure=[[3]],            # Branching layout; sets number of outputs
    task_names=['a', 'b', 'c'],
    task_types=['binary', 'multiclass', 'multilabel'],
    num_classes_per_task=[2, 5, 4],
    shared_layer_sizes=[256, 128],   # Optional dense stack before branches
    default_layer_sizes=[128, 64],   # Per-branch dense stacks (if not using branch_layer_sizes)
    encoder_config=encoder_config,
)

dropout_rate is not a ModelConfig field — pass it to MultiTaskModel(...):

model = MultiTaskModel(config, dropout_rate=training_config.dropout_rate)

The default falls back to 0.1 (matching TrainingConfig.dropout_rate's default).

EncoderConfig

EncoderConfig(
    encoder_integration=EncoderIntegration.TFHUB,
    encoder_input_type=EncoderInputType.TFHUB_TOKENS,
    encoder_identifier='...',
    embedding_dim=768,                # Pre-computed / no encoder
)

TrainingConfig

TrainingConfig(
    batch_size=32,
    epochs=10,
    learning_rate=2e-5,
    weight_decay_rate=0.01,
    dropout_rate=0.1,
    early_stopping=True,
    early_stopping_patience=3,
)

Troubleshooting

Import errors — install the missing package or the matching extra:

pip install tensorflow-hub             # ModuleNotFoundError: tensorflow_hub
pip install transformers               # ModuleNotFoundError: transformers
pip install 'multitask-py[huggingface]'   # ...or install the extra (includes transformers + torch)
pip install 'multitask-py[openai]'        # ModuleNotFoundError: openai
pip install 'multitask-py[regression]'    # ModuleNotFoundError: scipy

GPU issues:

import tensorflow as tf
print(tf.config.list_physical_devices('GPU'))

Out of memory:

from multitask import setup_gpu_memory_growth
setup_gpu_memory_growth()
# Or: TrainingConfig(batch_size=16)

NaN loss:

• Check labels are integers in valid range
• Reduce learning rate: learning_rate=1e-5

API Reference

Package exports (from multitask import ...): MultiTaskModel, Trainer, ModelConfig, TrainingConfig, EncoderConfig, load_model, and distributed helpers above.

Enums (import from multitask.config): EncoderIntegration, EncoderInputType.

Utils: load_model(), get_distribution_strategy(), setup_gpu_memory_growth(), check_distributed_compatibility(), print_device_info()

Examples

• examples/minimal_pipeline_example.py: Shortest full pipeline (NumPy + tf.data, train, evaluate, save/load)
• examples/hierarchical_pipeline_example.py: Two-level task_structure, same end-to-end flow
• examples/dataframe_pipeline_example.py: Pandas DataFrame → tf.data → train → evaluate
• examples/save_load_example.py: Model persistence
• examples/distributed_training.py: Distributed training
• examples/bert_multitask_example.py: BERT fine-tuning with hierarchical multi-task branching (requires [huggingface] extra)

Citation

@software{multitask_py,
    title = {multitask-py: A Flexible Multi-Task Learning Library for Natural Language Processing},
    author = {Mehlhaff, Isaac D. and Morucci, Marco and Ginting, Josephene and Tian, Eddie Ye},
    year = {2026},
    version = {1.0.1},
    url = {https://pypi.org/project/multitask-py/},
    repository = {https://github.com/imehlhaff/multitask}
}

See LICENSE.

Pull requests welcome.