Shows how to run Flux schnell under 17GBs without bells and whistles. It additionally shows how to serialize the quantized checkpoint and load it back.

inference_with_torchao_serialized.py

import torch
from huggingface_hub import hf_hub_download
from diffusers import FluxTransformer2DModel, DiffusionPipeline

dtype, device = torch.bfloat16, "cuda"
ckpt_id = "black-forest-labs/FLUX.1-schnell"

with torch.device("meta"):
    config = FluxTransformer2DModel.load_config(ckpt_id, subfolder="transformer")
    model = FluxTransformer2DModel.from_config(config).to(dtype)

ckpt_path = hf_hub_download(repo_id="sayakpaul/flux.1-schell-int8wo", filename="flux_schnell_int8wo.pt")
state_dict = torch.load(ckpt_path, map_location="cpu")
model.load_state_dict(state_dict, assign=True)

pipeline = DiffusionPipeline.from_pretrained(ckpt_id, transformer=model, torch_dtype=dtype).to("cuda")
image = pipeline(
	"cat", guidance_scale=0.0, num_inference_steps=4, max_sequence_length=256
).images[0]
image.save("flux_schnell_int8.png")

run_flux_schnell_torchao.py

# Install `torchao` from source: https://github.com/pytorch/ao
# Install PyTorch nightly

from diffusers import DiffusionPipeline, FluxTransformer2DModel, AutoencoderKL
from transformers import T5EncoderModel, CLIPTextModel
from torchao.quantization import quantize_, int8_weight_only
import torch 

ckpt_id = "black-forest-labs/FLUX.1-schnell"

# Quantize the components individually.
# If quality is taking a hit then don't quantize all components.
# Mix and match.

############ Diffusion Transformer ############
transformer = FluxTransformer2DModel.from_pretrained(
    ckpt_id, subfolder="transformer", torch_dtype=torch.bfloat16
)
quantize_(transformer, int8_weight_only())

############ Text Encoder ############
text_encoder = CLIPTextModel.from_pretrained(
    ckpt_id, subfolder="text_encoder", torch_dtype=torch.bfloat16
)
quantize_(text_encoder, int8_weight_only())

############ Text Encoder 2 ############
text_encoder_2 = T5EncoderModel.from_pretrained(
    ckpt_id, subfolder="text_encoder_2", torch_dtype=torch.bfloat16
)
quantize_(text_encoder_2, int8_weight_only())

############ VAE ############
vae = AutoencoderKL.from_pretrained(
    ckpt_id, subfolder="vae", torch_dtype=torch.bfloat16
)
quantize_(vae, int8_weight_only())

# Initialize the pipeline now.
pipeline = DiffusionPipeline.from_pretrained(
	ckpt_id, 
    transformer=transformer, 
    vae=vae,
    text_encoder=text_encoder, 
    text_encoder_2=text_encoder_2, 
    torch_dtype=torch.bfloat16
).to("cuda")
image = pipeline(
	"cat", guidance_scale=0.0, num_inference_steps=4, max_sequence_length=256
).images[0]

torch.cuda.empty_cache()
memory = (torch.cuda.memory_allocated() / 1024 / 1024 / 1024) 
print(f"{memory=:.3f} GB")

image.save("quantized_image.png")

serialize_with_torchao.py

from diffusers import FluxTransformer2DModel
from torchao.quantization import quantize_, int8_weight_only
import torch 

ckpt_id = "black-forest-labs/FLUX.1-schnell"

transformer = FluxTransformer2DModel.from_pretrained(
    ckpt_id, subfolder="transformer", torch_dtype=torch.bfloat16
)
quantize_(transformer, int8_weight_only())

# should ideally be possible with safetensors but
# https://github.com/huggingface/safetensors/issues/515
# this checkpoint is 12GB instead of 23GB.
torch.save(transformer.state_dict(), "flux_schnell_int8wo.pt")

@MostHumble
Getting an error running that code:
AttributeError: Can't get attribute 'PlainAQTLayout' on <module 'torchao.dtypes.affine_quantized_tensor' from '...Python\\Python311\\site-packages\\torchao\\dtypes\\affine_quantized_tensor.py'>
On torchao == 0.7.0

@tin2tin
Ended up having the same issue, reported it here: https://huggingface.co/sayakpaul/flux.1-schell-int8wo-improved/discussions/2#6783e9e49c52f42c530ff7c1

Please take the issue with torchao. Until it's resolved, either:

1. Use torchao integration from Diffusers.
2. Downgrade torchao installation.

Other than that, I can't provide additional suggestions.