#
torchao

torchao is a PyTorch architecture optimization library with support for custom high performance data types, quantization, and sparsity. It is composable with native PyTorch features such as torch.compile for even faster inference and training.

See the table below for additional torchao features.

Feature | Description
--- | ---
Quantization Aware Training (QAT) | Train quantized models with minimal accuracy loss (see QAT README)
Float8 Training | High-throughput training with float8 formats (see torchtitan and Accelerate docs)
Sparsity Support | Semi-structured (2:4) sparsity for faster inference (see Accelerating Neural Network Training with Semi-Structured (2:4) Sparsity blog post)
Optimizer Quantization | Reduce optimizer state memory with 4 and 8-bit variants of Adam
KV Cache Quantization | Enables long context inference with lower memory (see KV Cache Quantization)
Custom Kernels Support | use your own `torch.compile` compatible ops
FSDP2 | Composable with FSDP2 for training

Refer to the torchao README.md for more details about the library.

torchao supports the quantization techniques below.

- A16W8 Float8 Dynamic Quantization
- A16W8 Float8 WeightOnly Quantization
- A8W8 Int8 Dynamic Quantization
- A16W8 Int8 Weight Only Quantization
- A16W4 Int4 Weight Only Quantization
- Autoquantization

Check the table below to see if your hardware is compatible.

Component | Compatibility
--- | ---
CUDA Versions | ✅ cu118, cu126, cu128
CPU | ✅ change `device_map="cpu"` (see examples below)

Install torchao from PyPi or the PyTorch index with the following commands.

PyPi
PyTorch Index

    # Updating 🤗 Transformers to the latest version, as the example script below uses the new auto compilation
    # Stable release from Pypi which will default to CUDA 12.6
    pip install --upgrade torchao transformers

If your torcha version is below 0.10.0, you need to upgrade it, please refer to the deprecation notice for more details.

##
Quantization examples

TorchAO provides a variety of quantization configurations. Each configuration can be further customized with parameters such as `group_size`, `scheme`, and `layout` to optimize for specific hardware and model architectures.

For a complete list of available configurations, see the quantization API documentation.

You can manually choose the quantization types and settings or automatically select the quantization types.

Create a TorchAoConfig and specify the quantization type and `group_size` of the weights to quantize (for int8 weight only and int4 weight only). Set the `cache_implementation` to `"static"` to automatically torch.compile the forward method.

We’ll show examples for recommended quantization methods based on hardwares, e.g. A100 GPU, H100 GPU, CPU.

###
H100 GPU

float8-dynamic-and-weight-only
int4-weight-only

    import torch
    from transformers import TorchAoConfig, AutoModelForCausalLM, AutoTokenizer
    from torchao.quantization import Float8DynamicActivationFloat8WeightConfig

    quant_config = Float8DynamicActivationFloat8WeightConfig()
    # or float8 weight only quantization
    # quant_config = Float8WeightOnlyConfig()
    quantization_config = TorchAoConfig(quant_type=quant_config)

    # Load and quantize the model
    quantized_model = AutoModelForCausalLM.from_pretrained(
        "meta-llama/Llama-3.1-8B-Instruct",
        torch_dtype="auto",
        device_map="auto",
        quantization_config=quantization_config
    )

    tokenizer = AutoTokenizer.from_pretrained("meta-llama/Llama-3.1-8B-Instruct")
    input_text = "What are we having for dinner?"
    input_ids = tokenizer(input_text, return_tensors="pt").to("cuda")

    # auto-compile the quantized model with `cache_implementation="static"` to get speed up
    output = quantized_model.generate(**input_ids, max_new_tokens=10, cache_implementation="static")
    print(tokenizer.decode(output[0], skip_special_tokens=True))

###
A100 GPU

int8-dynamic-and-weight-only
int4-weight-only

    import torch
    from transformers import TorchAoConfig, AutoModelForCausalLM, AutoTokenizer
    from torchao.quantization import Int8DynamicActivationInt8WeightConfig

    quant_config = Int8DynamicActivationInt8WeightConfig()
    # or int8 weight only quantization
    # quant_config = Int8WeightOnlyConfig()
    quantization_config = TorchAoConfig(quant_type=quant_config)

    # Load and quantize the model
    quantized_model = AutoModelForCausalLM.from_pretrained(
        "meta-llama/Llama-3.1-8B-Instruct",
        torch_dtype="auto",
        device_map="auto",
        quantization_config=quantization_config
    )

    tokenizer = AutoTokenizer.from_pretrained("meta-llama/Llama-3.1-8B-Instruct")
    input_text = "What are we having for dinner?"
    input_ids = tokenizer(input_text, return_tensors="pt").to("cuda")

    # auto-compile the quantized model with `cache_implementation="static"` to get speed up
    output = quantized_model.generate(**input_ids, max_new_tokens=10, cache_implementation="static")
    print(tokenizer.decode(output[0], skip_special_tokens=True))

###
CPU

int8-dynamic-and-weight-only
int4-weight-only

    import torch
    from transformers import TorchAoConfig, AutoModelForCausalLM, AutoTokenizer
    from torchao.quantization import Int8DynamicActivationInt8WeightConfig

    quant_config = Int8DynamicActivationInt8WeightConfig()
    # quant_config = Int8WeightOnlyConfig()
    quantization_config = TorchAoConfig(quant_type=quant_config)

    # Load and quantize the model
    quantized_model = AutoModelForCausalLM.from_pretrained(
        "meta-llama/Llama-3.1-8B-Instruct",
        torch_dtype="auto",
        device_map="cpu",
        quantization_config=quantization_config
    )

    tokenizer = AutoTokenizer.from_pretrained("meta-llama/Llama-3.1-8B-Instruct")
    input_text = "What are we having for dinner?"
    input_ids = tokenizer(input_text, return_tensors="pt")

    # auto-compile the quantized model with `cache_implementation="static"` to get speed up
    output = quantized_model.generate(**input_ids, max_new_tokens=10, cache_implementation="static")
    print(tokenizer.decode(output[0], skip_special_tokens=True))

###
Autoquant

If you want to automatically choose a quantization type for quantizable layers (`nn.Linear`) you can use the autoquant API.

The `autoquant` API automatically chooses a quantization type by micro-benchmarking on input type and shape and compiling a single linear layer.

Note: autoquant is for GPU only right now.

Create a TorchAoConfig and set to `"autoquant"`. Set the `cache_implementation` to `"static"` to automatically torch.compile the forward method. Finally, call `finalize_autoquant` on the quantized model to finalize the quantization and log the input shapes.

    import torch
    from transformers import TorchAoConfig, AutoModelForCausalLM, AutoTokenizer

    quantization_config = TorchAoConfig("autoquant", min_sqnr=None)
    quantized_model = AutoModelForCausalLM.from_pretrained(
        "meta-llama/Llama-3.1-8B-Instruct",
        torch_dtype="auto",
        device_map="auto",
        quantization_config=quantization_config
    )

    tokenizer = AutoTokenizer.from_pretrained("meta-llama/Llama-3.1-8B-Instruct")
    input_text = "What are we having for dinner?"
    input_ids = tokenizer(input_text, return_tensors="pt").to("cuda")

    # auto-compile the quantized model with `cache_implementation="static"` to get speed up
    output = quantized_model.generate(**input_ids, max_new_tokens=10, cache_implementation="static")
    # explicitly call `finalize_autoquant` (may be refactored and removed in the future)
    quantized_model.finalize_autoquant()
    print(tokenizer.decode(output[0], skip_special_tokens=True))

##
Serialization

torchao implements torch.Tensor subclasses for maximum flexibility in supporting new quantized torch.Tensor formats. Safetensors serialization and deserialization does not work with torchao.

To avoid arbitrary user code execution, torchao sets `weights_only=True` in torch.load to ensure only tensors are loaded. Any known user functions can be whitelisted with add_safe_globals.

save-locally
push-to-huggingface-hub

    # don't serialize model with Safetensors
    output_dir = "llama3-8b-int4wo-128"
    quantized_model.save_pretrained("llama3-8b-int4wo-128", safe_serialization=False)

##
Loading quantized models

Loading a quantized model depends on the quantization scheme. For quantization schemes, like int8 and float8, you can quantize the model on any device and also load it on any device. The example below demonstrates quantizing a model on the CPU and then loading it on CUDA.

    import torch
    from transformers import TorchAoConfig, AutoModelForCausalLM, AutoTokenizer
    from torchao.quantization import Int8WeightOnlyConfig

    quant_config = Int8WeightOnlyConfig(group_size=128)
    quantization_config = TorchAoConfig(quant_type=quant_config)

    # Load and quantize the model
    quantized_model = AutoModelForCausalLM.from_pretrained(
        "meta-llama/Llama-3.1-8B-Instruct",
        torch_dtype="auto",
        device_map="cpu",
        quantization_config=quantization_config
    )
    # save the quantized model
    output_dir = "llama-3.1-8b-torchao-int8-cuda"
    quantized_model.save_pretrained(output_dir, safe_serialization=False)

    # reload the quantized model
    reloaded_model = AutoModelForCausalLM.from_pretrained(
        output_dir,
        device_map="auto",
        torch_dtype=torch.bfloat16
    )
    tokenizer = AutoTokenizer.from_pretrained("meta-llama/Llama-3.1-8B-Instruct")
    input_text = "What are we having for dinner?"
    input_ids = tokenizer(input_text, return_tensors="pt").to("cuda")

    output = reloaded_model.generate(**input_ids, max_new_tokens=10)
    print(tokenizer.decode(output[0], skip_special_tokens=True))

For int4, the model can only be loaded on the same device it was quantized on because the layout is specific to the device. The example below demonstrates quantizing and loading a model on the CPU.

    import torch
    from transformers import TorchAoConfig, AutoModelForCausalLM, AutoTokenizer
    from torchao.quantization import Int4WeightOnlyConfig
    from torchao.dtypes import Int4CPULayout

    quant_config = Int4WeightOnlyConfig(group_size=128, layout=Int4CPULayout())
    quantization_config = TorchAoConfig(quant_type=quant_config)

    # Load and quantize the model
    quantized_model = AutoModelForCausalLM.from_pretrained(
        "meta-llama/Llama-3.1-8B-Instruct",
        torch_dtype="auto",
        device_map="cpu",
        quantization_config=quantization_config
    )
    # save the quantized model
    output_dir = "llama-3.1-8b-torchao-int4-cpu"
    quantized_model.save_pretrained(output_dir, safe_serialization=False)

    # reload the quantized model
    reloaded_model = AutoModelForCausalLM.from_pretrained(
        output_dir,
        device_map="cpu",
        torch_dtype=torch.bfloat16
    )
    tokenizer = AutoTokenizer.from_pretrained("meta-llama/Llama-3.1-8B-Instruct")
    input_text = "What are we having for dinner?"
    input_ids = tokenizer(input_text, return_tensors="pt")

    output = reloaded_model.generate(**input_ids, max_new_tokens=10)
    print(tokenizer.decode(output[0], skip_special_tokens=True))

##
⚠️ Deprecation Notice

> Starting with version 0.10.0, the string-based API for quantization configuration (e.g., `TorchAoConfig("int4_weight_only", group_size=128)`) is deprecated and will be removed in a future release.

> Please use the new `AOBaseConfig`-based approach instead:

>     # Old way (deprecated)
>     quantization_config = TorchAoConfig("int4_weight_only", group_size=128)

>     # New way (recommended)
>     from torchao.quantization import Int4WeightOnlyConfig
>     quant_config = Int4WeightOnlyConfig(group_size=128)
>     quantization_config = TorchAoConfig(quant_type=quant_config)

> The new API offers greater flexibility, better type safety, and access to the full range of features available in torchao.

> Migration Guide

> Here’s how to migrate from common string identifiers to their `AOBaseConfig` equivalents:

> Old String API | New `AOBaseConfig` API
> --- | ---
> `"int4_weight_only"` | `Int4WeightOnlyConfig()`
> `"int8_weight_only"` | `Int8WeightOnlyConfig()`
> `"int8_dynamic_activation_int8_weight"` | `Int8DynamicActivationInt8WeightConfig()`

> All configuration objects accept parameters for customization (e.g., `group_size`, `scheme`, `layout`).

##
Resources

For a better sense of expected performance, view the benchmarks for various models with CUDA and XPU backends. You can also run the code below to benchmark a model yourself.

    from torch._inductor.utils import do_bench_using_profiling
    from typing import Callable

    def benchmark_fn(func: Callable, *args, **kwargs) -> float:
        """Thin wrapper around do_bench_using_profiling"""
        no_args = lambda: func(*args, **kwargs)
        time = do_bench_using_profiling(no_args)
        return time * 1e3

    MAX_NEW_TOKENS = 1000
    print("int4wo-128 model:", benchmark_fn(quantized_model.generate, **input_ids, max_new_tokens=MAX_NEW_TOKENS, cache_implementation="static"))

    bf16_model = AutoModelForCausalLM.from_pretrained(model_name, device_map="auto", torch_dtype=torch.bfloat16)
    output = bf16_model.generate(**input_ids, max_new_tokens=10, cache_implementation="static") # auto-compile
    print("bf16 model:", benchmark_fn(bf16_model.generate, **input_ids, max_new_tokens=MAX_NEW_TOKENS, cache_implementation="static"))

For best performance, you can use recommended settings by calling `torchao.quantization.utils.recommended_inductor_config_setter()`

Refer to Other Available Quantization Techniques for more examples and documentation.

##
Issues

If you encounter any issues with the Transformers integration, please open an issue on the Transformers repository. For issues directly related to torchao, please open an issue on the torchao repository.

< > Update on GitHub