From 36371c568968a4a67e8bd2d108c191078cfbe997 Mon Sep 17 00:00:00 2001
From: JerryZhou54 <zhouw.jerry2017@outlook.com>
Date: Tue, 26 Aug 2025 19:49:57 +0000
Subject: [PATCH] checkpoint

---
 .../configs/models/dits/causal_wanvideo.py    | 631 ++++++++++++++++++
 fastvideo/configs/models/dits/wanvideo.py     |   4 +
 2 files changed, 635 insertions(+)
 create mode 100644 fastvideo/configs/models/dits/causal_wanvideo.py

diff --git a/fastvideo/configs/models/dits/causal_wanvideo.py b/fastvideo/configs/models/dits/causal_wanvideo.py
new file mode 100644
index 000000000..405962448
--- /dev/null
+++ b/fastvideo/configs/models/dits/causal_wanvideo.py
@@ -0,0 +1,631 @@
+# SPDX-License-Identifier: Apache-2.0
+
+import math
+from typing import Any
+
+import numpy as np
+import torch
+import torch.nn as nn
+
+from torch.nn.attention.flex_attention import create_block_mask, flex_attention
+from torch.nn.attention.flex_attention import BlockMask
+# wan 1.3B model has a weird channel / head configurations and require max-autotune to work with flexattention
+# see https://github.com/pytorch/pytorch/issues/133254
+# change to default for other models
+flex_attention = torch.compile(
+    flex_attention, dynamic=False, mode="max-autotune-no-cudagraphs")
+import torch.distributed as dist
+
+import fastvideo.envs as envs
+from fastvideo.attention import (DistributedAttention,
+                                 LocalAttention)
+from fastvideo.configs.models.dits import WanVideoConfig
+from fastvideo.distributed.parallel_state import get_sp_world_size
+from fastvideo.forward_context import get_forward_context
+from fastvideo.layers.layernorm import (FP32LayerNorm, LayerNormScaleShift,
+                                        RMSNorm, ScaleResidual,
+                                        ScaleResidualLayerNormScaleShift)
+from fastvideo.layers.linear import ReplicatedLinear
+from fastvideo.layers.mlp import MLP
+from fastvideo.layers.rotary_embedding import (_apply_rotary_emb,
+                                               get_rotary_pos_embed)
+from fastvideo.layers.visual_embedding import (ModulateProjection, PatchEmbed,
+                                               TimestepEmbedder)
+from fastvideo.logger import init_logger
+from fastvideo.models.dits.base import BaseDiT
+from fastvideo.platforms import AttentionBackendEnum, current_platform
+
+logger = init_logger(__name__)
+
+
+class WanImageEmbedding(torch.nn.Module):
+
+    def __init__(self, in_features: int, out_features: int):
+        super().__init__()
+
+        self.norm1 = FP32LayerNorm(in_features)
+        self.ff = MLP(in_features, in_features, out_features, act_type="gelu")
+        self.norm2 = FP32LayerNorm(out_features)
+
+    def forward(self,
+                encoder_hidden_states_image: torch.Tensor) -> torch.Tensor:
+        dtype = encoder_hidden_states_image.dtype
+        hidden_states = self.norm1(encoder_hidden_states_image)
+        hidden_states = self.ff(hidden_states)
+        hidden_states = self.norm2(hidden_states).to(dtype)
+        return hidden_states
+
+
+class WanTimeTextImageEmbedding(nn.Module):
+
+    def __init__(
+        self,
+        dim: int,
+        time_freq_dim: int,
+        text_embed_dim: int,
+        image_embed_dim: int | None = None,
+    ):
+        super().__init__()
+
+        self.time_embedder = TimestepEmbedder(
+            dim, frequency_embedding_size=time_freq_dim, act_layer="silu")
+        self.time_modulation = ModulateProjection(dim,
+                                                  factor=6,
+                                                  act_layer="silu")
+        self.text_embedder = MLP(text_embed_dim,
+                                 dim,
+                                 dim,
+                                 bias=True,
+                                 act_type="gelu_pytorch_tanh")
+
+        self.image_embedder = None
+        if image_embed_dim is not None:
+            self.image_embedder = WanImageEmbedding(image_embed_dim, dim)
+
+    def forward(
+        self,
+        timestep: torch.Tensor,
+        encoder_hidden_states: torch.Tensor,
+        encoder_hidden_states_image: torch.Tensor | None = None,
+    ):
+        temb = self.time_embedder(timestep)
+        timestep_proj = self.time_modulation(temb)
+
+        encoder_hidden_states = self.text_embedder(encoder_hidden_states)
+        if encoder_hidden_states_image is not None:
+            assert self.image_embedder is not None
+            encoder_hidden_states_image = self.image_embedder(
+                encoder_hidden_states_image)
+
+        return temb, timestep_proj, encoder_hidden_states, encoder_hidden_states_image
+
+
+class WanSelfAttention(nn.Module):
+
+    def __init__(self,
+                 dim: int,
+                 num_heads: int,
+                 window_size=(-1, -1),
+                 qk_norm=True,
+                 eps=1e-6,
+                 parallel_attention=False) -> None:
+        assert dim % num_heads == 0
+        super().__init__()
+        self.dim = dim
+        self.num_heads = num_heads
+        self.head_dim = dim // num_heads
+        self.window_size = window_size
+        self.qk_norm = qk_norm
+        self.eps = eps
+        self.parallel_attention = parallel_attention
+
+        # layers
+        self.to_q = ReplicatedLinear(dim, dim)
+        self.to_k = ReplicatedLinear(dim, dim)
+        self.to_v = ReplicatedLinear(dim, dim)
+        self.to_out = ReplicatedLinear(dim, dim)
+        self.norm_q = RMSNorm(dim, eps=eps) if qk_norm else nn.Identity()
+        self.norm_k = RMSNorm(dim, eps=eps) if qk_norm else nn.Identity()
+
+        # Scaled dot product attention
+        self.attn = LocalAttention(
+            num_heads=num_heads,
+            head_size=self.head_dim,
+            dropout_rate=0,
+            softmax_scale=None,
+            causal=False,
+            supported_attention_backends=(AttentionBackendEnum.FLASH_ATTN,
+                                          AttentionBackendEnum.TORCH_SDPA))
+
+    def forward(self, x: torch.Tensor, context: torch.Tensor,
+                context_lens: int):
+        r"""
+        Args:
+            x(Tensor): Shape [B, L, num_heads, C / num_heads]
+            seq_lens(Tensor): Shape [B]
+            grid_sizes(Tensor): Shape [B, 3], the second dimension contains (F, H, W)
+            freqs(Tensor): Rope freqs, shape [1024, C / num_heads / 2]
+        """
+        pass
+
+
+class WanT2VCrossAttention(WanSelfAttention):
+
+    def forward(self, x, context, context_lens):
+        r"""
+        Args:
+            x(Tensor): Shape [B, L1, C]
+            context(Tensor): Shape [B, L2, C]
+            context_lens(Tensor): Shape [B]
+        """
+        b, n, d = x.size(0), self.num_heads, self.head_dim
+
+        # compute query, key, value
+        q = self.norm_q(self.to_q(x)[0]).view(b, -1, n, d)
+        k = self.norm_k(self.to_k(context)[0]).view(b, -1, n, d)
+        v = self.to_v(context)[0].view(b, -1, n, d)
+
+        # compute attention
+        x = self.attn(q, k, v)
+
+        # output
+        x = x.flatten(2)
+        x, _ = self.to_out(x)
+        return x
+
+class CausalWanTransformerBlock(nn.Module):
+
+    def __init__(self,
+                 dim: int,
+                 ffn_dim: int,
+                 num_heads: int,
+                 qk_norm: str = "rms_norm_across_heads",
+                 cross_attn_norm: bool = False,
+                 eps: float = 1e-6,
+                 added_kv_proj_dim: int | None = None,
+                 supported_attention_backends: tuple[AttentionBackendEnum, ...]
+                 | None = None,
+                 prefix: str = ""):
+        super().__init__()
+
+        # 1. Self-attention
+        self.norm1 = FP32LayerNorm(dim, eps, elementwise_affine=False)
+        self.to_q = ReplicatedLinear(dim, dim, bias=True)
+        self.to_k = ReplicatedLinear(dim, dim, bias=True)
+        self.to_v = ReplicatedLinear(dim, dim, bias=True)
+
+        self.to_out = ReplicatedLinear(dim, dim, bias=True)
+        self.attn1 = DistributedAttention(
+            num_heads=num_heads,
+            head_size=dim // num_heads,
+            causal=False,
+            supported_attention_backends=supported_attention_backends,
+            prefix=f"{prefix}.attn1")
+        self.hidden_dim = dim
+        self.num_attention_heads = num_heads
+        dim_head = dim // num_heads
+        if qk_norm == "rms_norm":
+            self.norm_q = RMSNorm(dim_head, eps=eps)
+            self.norm_k = RMSNorm(dim_head, eps=eps)
+        elif qk_norm == "rms_norm_across_heads":
+            # LTX applies qk norm across all heads
+            self.norm_q = RMSNorm(dim, eps=eps)
+            self.norm_k = RMSNorm(dim, eps=eps)
+        else:
+            print("QK Norm type not supported")
+            raise Exception
+        assert cross_attn_norm is True
+        self.self_attn_residual_norm = ScaleResidualLayerNormScaleShift(
+            dim,
+            norm_type="layer",
+            eps=eps,
+            elementwise_affine=True,
+            dtype=torch.float32,
+            compute_dtype=torch.float32)
+
+        # 2. Cross-attention
+        if added_kv_proj_dim is not None:
+            # I2V
+            self.attn2 = WanI2VCrossAttention(dim,
+                                              num_heads,
+                                              qk_norm=qk_norm,
+                                              eps=eps)
+        else:
+            # T2V
+            self.attn2 = WanT2VCrossAttention(dim,
+                                              num_heads,
+                                              qk_norm=qk_norm,
+                                              eps=eps)
+        self.cross_attn_residual_norm = ScaleResidualLayerNormScaleShift(
+            dim,
+            norm_type="layer",
+            eps=eps,
+            elementwise_affine=False,
+            dtype=torch.float32,
+            compute_dtype=torch.float32)
+
+        # 3. Feed-forward
+        self.ffn = MLP(dim, ffn_dim, act_type="gelu_pytorch_tanh")
+        self.mlp_residual = ScaleResidual()
+
+        self.scale_shift_table = nn.Parameter(torch.randn(1, 6, dim) / dim**0.5)
+
+    def forward(
+        self,
+        hidden_states: torch.Tensor,
+        encoder_hidden_states: torch.Tensor,
+        temb: torch.Tensor,
+        freqs_cis: tuple[torch.Tensor, torch.Tensor],
+    ) -> torch.Tensor:
+        if hidden_states.dim() == 4:
+            hidden_states = hidden_states.squeeze(1)
+        bs, seq_length, _ = hidden_states.shape
+        orig_dtype = hidden_states.dtype
+        # assert orig_dtype != torch.float32
+        e = self.scale_shift_table + temb.float()
+        shift_msa, scale_msa, gate_msa, c_shift_msa, c_scale_msa, c_gate_msa = e.chunk(
+            6, dim=1)
+        assert shift_msa.dtype == torch.float32
+
+        # 1. Self-attention
+        norm_hidden_states = (self.norm1(hidden_states.float()) *
+                              (1 + scale_msa) + shift_msa).to(orig_dtype)
+        query, _ = self.to_q(norm_hidden_states)
+        key, _ = self.to_k(norm_hidden_states)
+        value, _ = self.to_v(norm_hidden_states)
+
+        if self.norm_q is not None:
+            query = self.norm_q(query)
+        if self.norm_k is not None:
+            key = self.norm_k(key)
+
+        query = query.squeeze(1).unflatten(2, (self.num_attention_heads, -1))
+        key = key.squeeze(1).unflatten(2, (self.num_attention_heads, -1))
+        value = value.squeeze(1).unflatten(2, (self.num_attention_heads, -1))
+
+        # Apply rotary embeddings
+        cos, sin = freqs_cis
+        query, key = _apply_rotary_emb(query, cos, sin,
+                                       is_neox_style=False), _apply_rotary_emb(
+                                           key, cos, sin, is_neox_style=False)
+
+        attn_output, _ = self.attn1(query, key, value)
+        attn_output = attn_output.flatten(2)
+        attn_output, _ = self.to_out(attn_output)
+        attn_output = attn_output.squeeze(1)
+
+        null_shift = null_scale = torch.tensor([0], device=hidden_states.device)
+        norm_hidden_states, hidden_states = self.self_attn_residual_norm(
+            hidden_states, attn_output, gate_msa, null_shift, null_scale)
+        norm_hidden_states, hidden_states = norm_hidden_states.to(
+            orig_dtype), hidden_states.to(orig_dtype)
+
+        # 2. Cross-attention
+        attn_output = self.attn2(norm_hidden_states,
+                                 context=encoder_hidden_states,
+                                 context_lens=None)
+        norm_hidden_states, hidden_states = self.cross_attn_residual_norm(
+            hidden_states, attn_output, 1, c_shift_msa, c_scale_msa)
+        norm_hidden_states, hidden_states = norm_hidden_states.to(
+            orig_dtype), hidden_states.to(orig_dtype)
+
+        # 3. Feed-forward
+        ff_output = self.ffn(norm_hidden_states)
+        hidden_states = self.mlp_residual(hidden_states, ff_output, c_gate_msa)
+        hidden_states = hidden_states.to(orig_dtype)
+
+        return hidden_states
+
+class CausalWanTransformer3DModel(BaseDiT):
+    _fsdp_shard_conditions = WanVideoConfig()._fsdp_shard_conditions
+    _compile_conditions = WanVideoConfig()._compile_conditions
+    _supported_attention_backends = WanVideoConfig(
+    )._supported_attention_backends
+    param_names_mapping = WanVideoConfig().param_names_mapping
+    reverse_param_names_mapping = WanVideoConfig().reverse_param_names_mapping
+    lora_param_names_mapping = WanVideoConfig().lora_param_names_mapping
+
+    def __init__(self, config: WanVideoConfig, hf_config: dict[str,
+                                                               Any]) -> None:
+        super().__init__(config=config, hf_config=hf_config)
+
+        inner_dim = config.num_attention_heads * config.attention_head_dim
+        self.hidden_size = config.hidden_size
+        self.num_attention_heads = config.num_attention_heads
+        self.in_channels = config.in_channels
+        self.out_channels = config.out_channels
+        self.num_channels_latents = config.num_channels_latents
+        self.patch_size = config.patch_size
+        self.text_len = config.text_len
+        self.local_attn_size = config.local_attn_size
+
+        # 1. Patch & position embedding
+        self.patch_embedding = PatchEmbed(in_chans=config.in_channels,
+                                          embed_dim=inner_dim,
+                                          patch_size=config.patch_size,
+                                          flatten=False)
+
+        # 2. Condition embeddings
+        self.condition_embedder = WanTimeTextImageEmbedding(
+            dim=inner_dim,
+            time_freq_dim=config.freq_dim,
+            text_embed_dim=config.text_dim,
+            image_embed_dim=config.image_dim,
+        )
+
+        # 3. Transformer blocks
+        self.blocks = nn.ModuleList([
+            CausalWanTransformerBlock(inner_dim,
+                              config.ffn_dim,
+                              config.num_attention_heads,
+                              config.qk_norm,
+                              config.cross_attn_norm,
+                              config.eps,
+                              config.added_kv_proj_dim,
+                              self._supported_attention_backends,
+                              prefix=f"{config.prefix}.blocks.{i}")
+            for i in range(config.num_layers)
+        ])
+
+        # 4. Output norm & projection
+        self.norm_out = LayerNormScaleShift(inner_dim,
+                                            norm_type="layer",
+                                            eps=config.eps,
+                                            elementwise_affine=False,
+                                            dtype=torch.float32,
+                                            compute_dtype=torch.float32)
+        self.proj_out = nn.Linear(
+            inner_dim, config.out_channels * math.prod(config.patch_size))
+        self.scale_shift_table = nn.Parameter(
+            torch.randn(1, 2, inner_dim) / inner_dim**0.5)
+
+        self.gradient_checkpointing = False
+
+        # Causal-specific
+        self.block_mask = None
+        self.num_frame_per_block = 1
+        self.independent_first_frame = False
+
+        self.__post_init__()
+
+    @staticmethod
+    def _prepare_blockwise_causal_attn_mask(
+        device: torch.device | str, num_frames: int = 21,
+        frame_seqlen: int = 1560, num_frame_per_block=1, local_attn_size=-1
+    ) -> BlockMask:
+        """
+        we will divide the token sequence into the following format
+        [1 latent frame] [1 latent frame] ... [1 latent frame]
+        We use flexattention to construct the attention mask
+        """
+        total_length = num_frames * frame_seqlen
+
+        # we do right padding to get to a multiple of 128
+        padded_length = math.ceil(total_length / 128) * 128 - total_length
+
+        ends = torch.zeros(total_length + padded_length,
+                           device=device, dtype=torch.long)
+
+        # Block-wise causal mask will attend to all elements that are before the end of the current chunk
+        frame_indices = torch.arange(
+            start=0,
+            end=total_length,
+            step=frame_seqlen * num_frame_per_block,
+            device=device
+        )
+
+        for tmp in frame_indices:
+            ends[tmp:tmp + frame_seqlen * num_frame_per_block] = tmp + \
+                frame_seqlen * num_frame_per_block
+
+        def attention_mask(b, h, q_idx, kv_idx):
+            if local_attn_size == -1:
+                return (kv_idx < ends[q_idx]) | (q_idx == kv_idx)
+            else:
+                return ((kv_idx < ends[q_idx]) & (kv_idx >= (ends[q_idx] - local_attn_size * frame_seqlen))) | (q_idx == kv_idx)
+            # return ((kv_idx < total_length) & (q_idx < total_length))  | (q_idx == kv_idx) # bidirectional mask
+
+        block_mask = create_block_mask(attention_mask, B=None, H=None, Q_LEN=total_length + padded_length,
+                                       KV_LEN=total_length + padded_length, _compile=False, device=device)
+
+        if not dist.is_initialized() or dist.get_rank() == 0:
+            print(
+                f" cache a block wise causal mask with block size of {num_frame_per_block} frames")
+            print(block_mask)
+
+        # import imageio
+        # import numpy as np
+        # from torch.nn.attention.flex_attention import create_mask
+
+        # mask = create_mask(attention_mask, B=None, H=None, Q_LEN=total_length +
+        #                    padded_length, KV_LEN=total_length + padded_length, device=device)
+        # import cv2
+        # mask = cv2.resize(mask[0, 0].cpu().float().numpy(), (1024, 1024))
+        # imageio.imwrite("mask_%d.jpg" % (0), np.uint8(255. * mask))
+
+        return block_mask
+
+    def _forward_inference(
+                self,
+                hidden_states: torch.Tensor,
+                encoder_hidden_states: torch.Tensor | list[torch.Tensor],
+                timestep: torch.LongTensor,
+                encoder_hidden_states_image: torch.Tensor | list[torch.Tensor]
+                | None = None,
+                kv_cache: dict = None,
+                crossattn_cache: dict = None,
+                current_start: int = 0,
+                cache_start: int = 0,
+                **kwargs) -> torch.Tensor:
+        r"""
+        Run the diffusion model with kv caching.
+        See Algorithm 2 of CausVid paper https://arxiv.org/abs/2412.07772 for details.
+        This function will be run for num_frame times.
+        Process the latent frames one by one (1560 tokens each)
+        """
+
+        orig_dtype = hidden_states.dtype
+        if not isinstance(encoder_hidden_states, torch.Tensor):
+            encoder_hidden_states = encoder_hidden_states[0]
+        if isinstance(encoder_hidden_states_image,
+                      list) and len(encoder_hidden_states_image) > 0:
+            encoder_hidden_states_image = encoder_hidden_states_image[0]
+        else:
+            encoder_hidden_states_image = None
+
+        batch_size, num_channels, num_frames, height, width = hidden_states.shape
+        p_t, p_h, p_w = self.patch_size
+        post_patch_num_frames = num_frames // p_t
+        post_patch_height = height // p_h
+        post_patch_width = width // p_w
+
+        # Get rotary embeddings
+        d = self.hidden_size // self.num_attention_heads
+        rope_dim_list = [d - 4 * (d // 6), 2 * (d // 6), 2 * (d // 6)]
+        freqs_cos, freqs_sin = get_rotary_pos_embed(
+            (post_patch_num_frames * get_sp_world_size(), post_patch_height,
+             post_patch_width),
+            self.hidden_size,
+            self.num_attention_heads,
+            rope_dim_list,
+            dtype=torch.float32 if current_platform.is_mps() else torch.float64,
+            rope_theta=10000)
+        freqs_cos = freqs_cos.to(hidden_states.device)
+        freqs_sin = freqs_sin.to(hidden_states.device)
+        freqs_cis = (freqs_cos.float(),
+                     freqs_sin.float()) if freqs_cos is not None else None
+
+        hidden_states = self.patch_embedding(hidden_states)
+        hidden_states = hidden_states.flatten(2).transpose(1, 2)
+
+        temb, timestep_proj, encoder_hidden_states, encoder_hidden_states_image = self.condition_embedder(
+            timestep, encoder_hidden_states, encoder_hidden_states_image)
+        timestep_proj = timestep_proj.unflatten(1, (6, -1))
+
+        if encoder_hidden_states_image is not None:
+            encoder_hidden_states = torch.concat(
+                [encoder_hidden_states_image, encoder_hidden_states], dim=1)
+
+        encoder_hidden_states = encoder_hidden_states.to(
+            orig_dtype) if current_platform.is_mps(
+            ) else encoder_hidden_states  # cast to orig_dtype for MPS
+
+        assert encoder_hidden_states.dtype == orig_dtype
+
+        # 4. Transformer blocks
+        if torch.is_grad_enabled() and self.gradient_checkpointing:
+            for block in self.blocks:
+                hidden_states = self._gradient_checkpointing_func(
+                    block, hidden_states, encoder_hidden_states,
+                    timestep_proj, freqs_cis)
+        else:
+            for block in self.blocks:
+                hidden_states = block(hidden_states, encoder_hidden_states,
+                                        timestep_proj, freqs_cis)
+
+        # 5. Output norm, projection & unpatchify
+        shift, scale = (self.scale_shift_table + temb.unsqueeze(1)).chunk(2,
+                                                                          dim=1)
+        hidden_states = self.norm_out(hidden_states, shift, scale)
+        hidden_states = self.proj_out(hidden_states)
+
+        hidden_states = hidden_states.reshape(batch_size, post_patch_num_frames,
+                                              post_patch_height,
+                                              post_patch_width, p_t, p_h, p_w,
+                                              -1)
+        hidden_states = hidden_states.permute(0, 7, 1, 4, 2, 5, 3, 6)
+        output = hidden_states.flatten(6, 7).flatten(4, 5).flatten(2, 3)
+
+        return output
+
+    def _forward_train(self,
+                hidden_states: torch.Tensor,
+                encoder_hidden_states: torch.Tensor | list[torch.Tensor],
+                timestep: torch.LongTensor,
+                encoder_hidden_states_image: torch.Tensor | list[torch.Tensor]
+                | None = None,
+                **kwargs) -> torch.Tensor:
+
+        orig_dtype = hidden_states.dtype
+        if not isinstance(encoder_hidden_states, torch.Tensor):
+            encoder_hidden_states = encoder_hidden_states[0]
+        if isinstance(encoder_hidden_states_image,
+                      list) and len(encoder_hidden_states_image) > 0:
+            encoder_hidden_states_image = encoder_hidden_states_image[0]
+        else:
+            encoder_hidden_states_image = None
+
+        batch_size, num_channels, num_frames, height, width = hidden_states.shape
+        p_t, p_h, p_w = self.patch_size
+        post_patch_num_frames = num_frames // p_t
+        post_patch_height = height // p_h
+        post_patch_width = width // p_w
+
+        # Get rotary embeddings
+        d = self.hidden_size // self.num_attention_heads
+        rope_dim_list = [d - 4 * (d // 6), 2 * (d // 6), 2 * (d // 6)]
+        freqs_cos, freqs_sin = get_rotary_pos_embed(
+            (post_patch_num_frames * get_sp_world_size(), post_patch_height,
+             post_patch_width),
+            self.hidden_size,
+            self.num_attention_heads,
+            rope_dim_list,
+            dtype=torch.float32 if current_platform.is_mps() else torch.float64,
+            rope_theta=10000)
+        freqs_cos = freqs_cos.to(hidden_states.device)
+        freqs_sin = freqs_sin.to(hidden_states.device)
+        freqs_cis = (freqs_cos.float(),
+                     freqs_sin.float()) if freqs_cos is not None else None
+
+        hidden_states = self.patch_embedding(hidden_states)
+        hidden_states = hidden_states.flatten(2).transpose(1, 2)
+
+        temb, timestep_proj, encoder_hidden_states, encoder_hidden_states_image = self.condition_embedder(
+            timestep, encoder_hidden_states, encoder_hidden_states_image)
+        timestep_proj = timestep_proj.unflatten(1, (6, -1))
+
+        if encoder_hidden_states_image is not None:
+            encoder_hidden_states = torch.concat(
+                [encoder_hidden_states_image, encoder_hidden_states], dim=1)
+
+        encoder_hidden_states = encoder_hidden_states.to(
+            orig_dtype) if current_platform.is_mps(
+            ) else encoder_hidden_states  # cast to orig_dtype for MPS
+
+        assert encoder_hidden_states.dtype == orig_dtype
+
+        # 4. Transformer blocks
+        if torch.is_grad_enabled() and self.gradient_checkpointing:
+            for block in self.blocks:
+                hidden_states = self._gradient_checkpointing_func(
+                    block, hidden_states, encoder_hidden_states,
+                    timestep_proj, freqs_cis)
+        else:
+            for block in self.blocks:
+                hidden_states = block(hidden_states, encoder_hidden_states,
+                                        timestep_proj, freqs_cis)
+
+        # 5. Output norm, projection & unpatchify
+        shift, scale = (self.scale_shift_table + temb.unsqueeze(1)).chunk(2,
+                                                                          dim=1)
+        hidden_states = self.norm_out(hidden_states, shift, scale)
+        hidden_states = self.proj_out(hidden_states)
+
+        hidden_states = hidden_states.reshape(batch_size, post_patch_num_frames,
+                                              post_patch_height,
+                                              post_patch_width, p_t, p_h, p_w,
+                                              -1)
+        hidden_states = hidden_states.permute(0, 7, 1, 4, 2, 5, 3, 6)
+        output = hidden_states.flatten(6, 7).flatten(4, 5).flatten(2, 3)
+
+        return output
+
+    def forward(
+        self,
+        *args,
+        **kwargs
+    ):
+        if kwargs.get('kv_cache', None) is not None:
+            return self._forward_inference(*args, **kwargs)
+        else:
+            return self._forward_train(*args, **kwargs)
diff --git a/fastvideo/configs/models/dits/wanvideo.py b/fastvideo/configs/models/dits/wanvideo.py
index 8cd25cf6c..d31a3a607 100644
--- a/fastvideo/configs/models/dits/wanvideo.py
+++ b/fastvideo/configs/models/dits/wanvideo.py
@@ -92,6 +92,10 @@ class WanVideoArchConfig(DiTArchConfig):
     pos_embed_seq_len: int | None = None
     exclude_lora_layers: list[str] = field(default_factory=lambda: ["embedder"])
 
+    # Causal Wan
+    local_attn_size: int = -1 # Window size for temporal local attention (-1 indicates global attention)
+    sink_size: int = 0 # Size of the attention sink, we keep the first `sink_size` frames unchanged when rolling the KV cache
+
     def __post_init__(self):
         super().__post_init__()
         self.out_channels = self.out_channels or self.in_channels