diff --git a/modules/model/QwenModel.py b/modules/model/QwenModel.py
index afa6c24fe..71de80320 100644
--- a/modules/model/QwenModel.py
+++ b/modules/model/QwenModel.py
@@ -177,8 +177,8 @@ def encode_text(
         #pad to 16 because attention processors and/or torch.compile can have issues with uneven sequence lengths, but only pad if an attention mask has to be used anyway:
         #TODO the second condition could trigger https://github.com/pytorch/pytorch/issues/165506 again, but try like this because no attention mask
         #is preferable: https://github.com/Nerogar/OneTrainer/pull/1109
-        if max_seq_length % 16 > 0 and (seq_lengths != max_seq_length).any():
-            max_seq_length += (16 - max_seq_length % 16)
+        if max_seq_length % 64 > 0 and (seq_lengths != max_seq_length).any():
+            max_seq_length += (64 - max_seq_length % 64)
 
         text_encoder_output = text_encoder_output[:, :max_seq_length, :]
         bool_attention_mask = tokens_mask[:, :max_seq_length].bool()
diff --git a/modules/modelSampler/QwenSampler.py b/modules/modelSampler/QwenSampler.py
index 798bc54cd..0fc27c7a0 100644
--- a/modules/modelSampler/QwenSampler.py
+++ b/modules/modelSampler/QwenSampler.py
@@ -97,9 +97,6 @@ def __sample_base(
             if "generator" in set(inspect.signature(noise_scheduler.step).parameters.keys()):
                 extra_step_kwargs["generator"] = generator #TODO purpose?
 
-            #txt_seq_lens = text_attention_mask.sum(dim=1).tolist()
-            txt_seq_lens = [text_attention_mask.shape[1]] * text_attention_mask.shape[0]
-
             #FIXME list of lists is not according to type hint, but according to diffusers code
             #https://github.com/huggingface/diffusers/issues/12295
             img_shapes = [[(
@@ -110,12 +107,6 @@ def __sample_base(
 
             self.model.transformer_to(self.train_device)
 
-            #FIXME bug workaround for https://github.com/huggingface/diffusers/issues/12294
-            image_seq_len = latent_image.shape[1]
-            image_attention_mask=torch.ones((batch_size, image_seq_len), dtype=torch.bool, device=latent_image.device)
-            attention_mask = torch.cat([text_attention_mask, image_attention_mask], dim=1)
-            attention_mask_2d = attention_mask[:, None, None, :] * attention_mask[:, None, :, None]
-
             for i, timestep in enumerate(tqdm(timesteps, desc="sampling")):
                 latent_model_input = torch.cat([latent_image] * batch_size)
                 expanded_timestep = timestep.expand(batch_size)
@@ -123,12 +114,8 @@ def __sample_base(
                     hidden_states=latent_model_input.to(dtype=self.model.train_dtype.torch_dtype()),
                     timestep=expanded_timestep / 1000,
                     encoder_hidden_states=combined_prompt_embedding.to(dtype=self.model.train_dtype.torch_dtype()),
-                    encoder_hidden_states_mask=text_attention_mask,
-                    txt_seq_lens=txt_seq_lens,
+                    encoder_hidden_states_mask=text_attention_mask if not torch.all(text_attention_mask) else None,
                     img_shapes=img_shapes,
-                    attention_kwargs = {
-                        "attention_mask": attention_mask_2d,
-                    },
                     return_dict=True
                 ).sample
 
diff --git a/modules/modelSetup/BaseChromaSetup.py b/modules/modelSetup/BaseChromaSetup.py
index 7a7847df7..25ed8d155 100644
--- a/modules/modelSetup/BaseChromaSetup.py
+++ b/modules/modelSetup/BaseChromaSetup.py
@@ -86,6 +86,8 @@ def setup_optimizations(
         quantize_layers(model.vae, self.train_device, model.train_dtype, config)
         quantize_layers(model.transformer, self.train_device, model.train_dtype, config)
 
+        self._set_attention_backend(model.transformer, config.attention_mechanism, mask=True)
+
     def _setup_embeddings(
             self,
             model: ChromaModel,
diff --git a/modules/modelSetup/BaseFluxSetup.py b/modules/modelSetup/BaseFluxSetup.py
index 1865f382e..621837d17 100644
--- a/modules/modelSetup/BaseFluxSetup.py
+++ b/modules/modelSetup/BaseFluxSetup.py
@@ -89,6 +89,8 @@ def setup_optimizations(
         quantize_layers(model.vae, self.train_device, model.train_dtype, config)
         quantize_layers(model.transformer, self.train_device, model.train_dtype, config)
 
+        self._set_attention_backend(model.transformer, config.attention_mechanism, mask=False)
+
     def _setup_embeddings(
             self,
             model: FluxModel,
diff --git a/modules/modelSetup/BaseHiDreamSetup.py b/modules/modelSetup/BaseHiDreamSetup.py
index 48e691ecd..b9e646272 100644
--- a/modules/modelSetup/BaseHiDreamSetup.py
+++ b/modules/modelSetup/BaseHiDreamSetup.py
@@ -105,6 +105,8 @@ def setup_optimizations(
         quantize_layers(model.vae, self.train_device, model.train_dtype, config)
         quantize_layers(model.transformer, self.train_device, model.transformer_train_dtype, config)
 
+        self._set_attention_backend(model.transformer, config.attention_mechanism, mask=True)
+
     def _setup_embeddings(
             self,
             model: HiDreamModel,
diff --git a/modules/modelSetup/BaseHunyuanVideoSetup.py b/modules/modelSetup/BaseHunyuanVideoSetup.py
index bbb90b71a..ddec0b122 100644
--- a/modules/modelSetup/BaseHunyuanVideoSetup.py
+++ b/modules/modelSetup/BaseHunyuanVideoSetup.py
@@ -91,6 +91,8 @@ def setup_optimizations(
         quantize_layers(model.transformer, self.train_device, model.transformer_train_dtype, config)
 
         model.vae.enable_tiling()
+        self._set_attention_backend(model.transformer, config.attention_mechanism, mask=True)
+
 
     def _setup_embeddings(
             self,
diff --git a/modules/modelSetup/BaseModelSetup.py b/modules/modelSetup/BaseModelSetup.py
index 5b0e7df95..a4f8384c4 100644
--- a/modules/modelSetup/BaseModelSetup.py
+++ b/modules/modelSetup/BaseModelSetup.py
@@ -3,6 +3,7 @@
 
 from modules.model.BaseModel import BaseModel
 from modules.util.config.TrainConfig import TrainConfig, TrainEmbeddingConfig, TrainModelPartConfig
+from modules.util.enum.AttentionMechanism import AttentionMechanism
 from modules.util.enum.TrainingMethod import TrainingMethod
 from modules.util.ModuleFilter import ModuleFilter
 from modules.util.NamedParameterGroup import NamedParameterGroup, NamedParameterGroupCollection
@@ -235,3 +236,21 @@ def _setup_model_part_requires_grad(
             if unique_name in self.frozen_parameters:
                 for param in self.frozen_parameters[unique_name]:
                     param.requires_grad_(False)
+
+    @staticmethod
+    def _set_attention_backend(component, attn: AttentionMechanism, mask: bool=False, varlen: bool=False):
+        match attn:
+            case AttentionMechanism.SDP:
+                component.set_attention_backend("native")
+            case AttentionMechanism.FLASH:
+                if mask or varlen:
+                    print("Warning: FLASH attention might fail for this model, depending on other configuration (batch size > 1, etc.)")
+                component.set_attention_backend("flash")
+            case AttentionMechanism.SPLIT:
+                component.set_attention_backend("native_split")
+            case AttentionMechanism.FLASH_SPLIT:
+                component.set_attention_backend("flash_split")
+                if mask and not varlen:
+                    print("Warning: FLASH attention might fail for this model, depending on other configuration (batch size > 1, etc.)")
+            case _:
+                raise NotImplementedError(f"attention mechanism {str(attn)} not implemented")
diff --git a/modules/modelSetup/BasePixArtAlphaSetup.py b/modules/modelSetup/BasePixArtAlphaSetup.py
index 8240fb5f4..38993344e 100644
--- a/modules/modelSetup/BasePixArtAlphaSetup.py
+++ b/modules/modelSetup/BasePixArtAlphaSetup.py
@@ -85,6 +85,7 @@ def setup_optimizations(
         quantize_layers(model.text_encoder, self.train_device, model.text_encoder_train_dtype, config)
         quantize_layers(model.vae, self.train_device, model.train_dtype, config)
         quantize_layers(model.transformer, self.train_device, model.train_dtype, config)
+        self._set_attention_backend(model.transformer, config.attention_mechanism, mask=True)
 
     def _setup_embeddings(
             self,
diff --git a/modules/modelSetup/BaseQwenSetup.py b/modules/modelSetup/BaseQwenSetup.py
index dc7115274..2d6ad58db 100644
--- a/modules/modelSetup/BaseQwenSetup.py
+++ b/modules/modelSetup/BaseQwenSetup.py
@@ -80,6 +80,7 @@ def setup_optimizations(
         quantize_layers(model.text_encoder, self.train_device, model.text_encoder_train_dtype, config)
         quantize_layers(model.vae, self.train_device, model.train_dtype, config)
         quantize_layers(model.transformer, self.train_device, model.train_dtype, config)
+        self._set_attention_backend(model.transformer, config.attention_mechanism, varlen=True)
 
     def predict(
             self,
@@ -131,11 +132,6 @@ def predict(
             latent_input = scaled_noisy_latent_image
             packed_latent_input = model.pack_latents(latent_input)
 
-            #FIXME this is the only case that the transformer accepts:
-            #see https://github.com/huggingface/diffusers/issues/12344
-            #actual text sequence lengths can be shorter,but they might be padded and masked
-            txt_seq_lens = [text_encoder_output.shape[1]] * text_encoder_output.shape[0]
-
             #FIXME list of lists is not according to type hint, but according to diffusers code:
             #https://github.com/huggingface/diffusers/issues/12295
             img_shapes = [[(
@@ -144,21 +140,12 @@ def predict(
                 latent_input.shape[-1] // 2)
             ]] * latent_input.shape[0]
 
-            #FIXME bug workaround for https://github.com/huggingface/diffusers/issues/12294
-            image_attention_mask=torch.ones((packed_latent_input.shape[0], packed_latent_input.shape[1]), dtype=torch.bool, device=latent_image.device)
-            attention_mask = torch.cat([text_attention_mask, image_attention_mask], dim=1)
-            attention_mask_2d = attention_mask[:, None, None, :] if not torch.all(text_attention_mask) else None
-
             packed_predicted_flow = model.transformer(
                 hidden_states=packed_latent_input.to(dtype=model.train_dtype.torch_dtype()),
                 timestep=timestep / 1000,
                 encoder_hidden_states=text_encoder_output.to(dtype=model.train_dtype.torch_dtype()),
-                encoder_hidden_states_mask=text_attention_mask,
-                txt_seq_lens=txt_seq_lens,
+                encoder_hidden_states_mask=text_attention_mask if not torch.all(text_attention_mask) else None,
                 img_shapes=img_shapes,
-                attention_kwargs = {
-                    "attention_mask": attention_mask_2d,
-                },
                 return_dict=True,
             ).sample
 
diff --git a/modules/modelSetup/BaseSanaSetup.py b/modules/modelSetup/BaseSanaSetup.py
index 84078ff6f..a9b49bd11 100644
--- a/modules/modelSetup/BaseSanaSetup.py
+++ b/modules/modelSetup/BaseSanaSetup.py
@@ -97,6 +97,7 @@ def setup_optimizations(
         quantize_layers(model.text_encoder, self.train_device, model.text_encoder_train_dtype, config)
         quantize_layers(model.vae, self.train_device, model.train_dtype, config)
         quantize_layers(model.transformer, self.train_device, model.train_dtype, config)
+        self._set_attention_backend(model.transformer, config.attention_mechanism, mask=True)
 
     def _setup_embeddings(
             self,
diff --git a/modules/modelSetup/BaseStableDiffusion3Setup.py b/modules/modelSetup/BaseStableDiffusion3Setup.py
index 5015b21af..af07860c3 100644
--- a/modules/modelSetup/BaseStableDiffusion3Setup.py
+++ b/modules/modelSetup/BaseStableDiffusion3Setup.py
@@ -91,6 +91,7 @@ def setup_optimizations(
         quantize_layers(model.text_encoder_3, self.train_device, model.text_encoder_3_train_dtype, config)
         quantize_layers(model.vae, self.train_device, model.train_dtype, config)
         quantize_layers(model.transformer, self.train_device, model.train_dtype, config)
+        self._set_attention_backend(model.transformer, config.attention_mechanism)
 
     def _setup_embeddings(
             self,
diff --git a/modules/modelSetup/BaseStableDiffusionSetup.py b/modules/modelSetup/BaseStableDiffusionSetup.py
index 0fc6ed0df..020081fb5 100644
--- a/modules/modelSetup/BaseStableDiffusionSetup.py
+++ b/modules/modelSetup/BaseStableDiffusionSetup.py
@@ -71,6 +71,7 @@ def setup_optimizations(
         quantize_layers(model.text_encoder, self.train_device, model.train_dtype, config)
         quantize_layers(model.vae, self.train_device, model.train_dtype, config)
         quantize_layers(model.unet, self.train_device, model.train_dtype, config)
+        self._set_attention_backend(model.unet, config.attention_mechanism)
 
     def _setup_embeddings(
             self,
diff --git a/modules/modelSetup/BaseStableDiffusionXLSetup.py b/modules/modelSetup/BaseStableDiffusionXLSetup.py
index 37121951a..eb842a884 100644
--- a/modules/modelSetup/BaseStableDiffusionXLSetup.py
+++ b/modules/modelSetup/BaseStableDiffusionXLSetup.py
@@ -80,6 +80,7 @@ def setup_optimizations(
         quantize_layers(model.text_encoder_2, self.train_device, model.train_dtype, config)
         quantize_layers(model.vae, self.train_device, model.vae_train_dtype, config)
         quantize_layers(model.unet, self.train_device, model.train_dtype, config)
+        self._set_attention_backend(model.unet, config.attention_mechanism)
 
     def _setup_embeddings(
             self,
diff --git a/modules/modelSetup/BaseZImageSetup.py b/modules/modelSetup/BaseZImageSetup.py
index 727122f8b..d5f4628df 100644
--- a/modules/modelSetup/BaseZImageSetup.py
+++ b/modules/modelSetup/BaseZImageSetup.py
@@ -81,6 +81,7 @@ def setup_optimizations(
         quantize_layers(model.text_encoder, self.train_device, model.text_encoder_train_dtype, config)
         quantize_layers(model.vae, self.train_device, model.train_dtype, config)
         quantize_layers(model.transformer, self.train_device, model.train_dtype, config)
+        self._set_attention_backend(model.transformer, config.attention_mechanism, mask=True)
 
     def predict(
             self,
diff --git a/modules/ui/TrainingTab.py b/modules/ui/TrainingTab.py
index 9cc2bcec8..49db1a363 100644
--- a/modules/ui/TrainingTab.py
+++ b/modules/ui/TrainingTab.py
@@ -15,6 +15,7 @@
 from modules.ui.SchedulerParamsWindow import SchedulerParamsWindow
 from modules.ui.TimestepDistributionWindow import TimestepDistributionWindow
 from modules.util.config.TrainConfig import TrainConfig
+from modules.util.enum.AttentionMechanism import AttentionMechanism
 from modules.util.enum.DataType import DataType
 from modules.util.enum.EMAMode import EMAMode
 from modules.util.enum.GradientCheckpointingMethod import GradientCheckpointingMethod
@@ -336,6 +337,13 @@ def __create_base2_frame(self, master, row, video_training_enabled: bool = False
         frame.grid_columnconfigure(0, weight=1)
         row = 0
 
+        # attention mechanism
+        components.label(frame, row, 0, "Attention",
+                         tooltip="The attention mechanism used during training. Use `SPLIT` on linux. On windows, use 'SDP' or `FLASH_SPLIT`. 'FLASH_SPLIT' can be faster but you have to install it, and it does not support all models. For very high batch sizes, the SPLIT variants might be slower.")
+        components.options(frame, row, 1, [str(x) for x in list(AttentionMechanism)], self.ui_state,
+                           "attention_mechanism")
+        row += 1
+
         # ema
         components.label(frame, row, 0, "EMA",
                          tooltip="EMA averages the training progress over many steps, better preserving different concepts in big datasets")
diff --git a/modules/util/config/TrainConfig.py b/modules/util/config/TrainConfig.py
index ddaee4b89..1873008c8 100644
--- a/modules/util/config/TrainConfig.py
+++ b/modules/util/config/TrainConfig.py
@@ -9,6 +9,7 @@
 from modules.util.config.ConceptConfig import ConceptConfig
 from modules.util.config.SampleConfig import SampleConfig
 from modules.util.config.SecretsConfig import SecretsConfig
+from modules.util.enum.AttentionMechanism import AttentionMechanism
 from modules.util.enum.AudioFormat import AudioFormat
 from modules.util.enum.ConfigPart import ConfigPart
 from modules.util.enum.DataType import DataType
@@ -422,6 +423,7 @@ class TrainConfig(BaseConfig):
     only_cache: bool
     resolution: str
     frames: str
+    attention_mechanism: AttentionMechanism
     mse_strength: float
     mae_strength: float
     log_cosh_strength: float
@@ -1005,6 +1007,7 @@ def default_values() -> 'TrainConfig':
         data.append(("only_cache", False, bool, False))
         data.append(("resolution", "512", str, False))
         data.append(("frames", "25", str, False))
+        data.append(("attention_mechanism", AttentionMechanism.SDP, AttentionMechanism, False))
         data.append(("mse_strength", 1.0, float, False))
         data.append(("mae_strength", 0.0, float, False))
         data.append(("log_cosh_strength", 0.0, float, False))
diff --git a/modules/util/enum/AttentionMechanism.py b/modules/util/enum/AttentionMechanism.py
new file mode 100644
index 000000000..a5e2d5e96
--- /dev/null
+++ b/modules/util/enum/AttentionMechanism.py
@@ -0,0 +1,11 @@
+from enum import Enum
+
+
+class AttentionMechanism(Enum):
+    SDP = 'SDP'
+    FLASH = 'FLASH'
+    SPLIT = 'SPLIT'
+    FLASH_SPLIT = 'FLASH_SPLIT'
+
+    def __str__(self):
+        return self.value
diff --git a/requirements-global.txt b/requirements-global.txt
index afa429bf2..829ebedd0 100644
--- a/requirements-global.txt
+++ b/requirements-global.txt
@@ -20,7 +20,7 @@ pytorch-lightning==2.5.1.post0
 
 # diffusion models
 #Note: check whether Qwen bugs in diffusers have been fixed before upgrading diffusers (see BaseQwenSetup):
--e git+https://github.com/huggingface/diffusers.git@256e010#egg=diffusers
+-e git+https://github.com/dxqb/diffusers.git@split_attention#egg=diffusers
 gguf==0.17.1
 transformers==4.56.2
 sentencepiece==0.2.1 # transitive dependency of transformers for tokenizer loading