diff --git a/README.md b/README.md
index d2403c7..dabf3f2 100644
--- a/README.md
+++ b/README.md
@@ -108,9 +108,12 @@ unet = SpaceTimeUnet(
     dim = 64,
     channels = 3,
     dim_mult = (1, 2, 4, 8),
+    resnet_block_depths = (1, 1, 1, 2),
     temporal_compression = (False, False, False, True),
     self_attns = (False, False, False, True),
-    condition_on_timestep = False
+    condition_on_timestep = False,
+    attn_pos_bias = False,
+    flash_attn = True
 ).cuda()
 
 # train on images
@@ -136,8 +139,8 @@ video_as_images_out = unet(video, enable_time = False)
 
 - [x] give attention the best positional embeddings research has to offer
 - [x] soup up the attention
+- [x] add flash attention
 
-- [ ] add flash attention
 - [ ] make sure dalle2-pytorch can accept `SpaceTimeUnet` for training
 
 ## Citations
@@ -187,3 +190,12 @@ video_as_images_out = unet(video, enable_time = False)
     url     = {https://openreview.net/forum?id=GMYWzWztDx5},
 }
 ```
+
+```bibtex
+@inproceedings{dao2022flashattention,
+    title   = {Flash{A}ttention: Fast and Memory-Efficient Exact Attention with {IO}-Awareness},
+    author  = {Dao, Tri and Fu, Daniel Y. and Ermon, Stefano and Rudra, Atri and R{\'e}, Christopher},
+    booktitle = {Advances in Neural Information Processing Systems},
+    year    = {2022}
+}
+```
diff --git a/make_a_video_pytorch/attend.py b/make_a_video_pytorch/attend.py
new file mode 100644
index 0000000..ef23a23
--- /dev/null
+++ b/make_a_video_pytorch/attend.py
@@ -0,0 +1,114 @@
+from functools import wraps
+from packaging import version
+from collections import namedtuple
+
+import torch
+from torch import nn, einsum
+import torch.nn.functional as F
+
+from einops import rearrange
+
+# constants
+
+AttentionConfig = namedtuple('AttentionConfig', ['enable_flash', 'enable_math', 'enable_mem_efficient'])
+
+# helpers
+
+def exists(val):
+    return val is not None
+
+def once(fn):
+    called = False
+    @wraps(fn)
+    def inner(x):
+        nonlocal called
+        if called:
+            return
+        called = True
+        return fn(x)
+    return inner
+
+print_once = once(print)
+
+# main class
+
+class Attend(nn.Module):
+    def __init__(
+        self,
+        dropout = 0.,
+        flash = False
+    ):
+        super().__init__()
+        self.dropout = dropout
+        self.attn_dropout = nn.Dropout(dropout)
+
+        self.flash = flash
+        assert not (flash and version.parse(torch.__version__) < version.parse('2.0.0')), 'in order to use flash attention, you must be using pytorch 2.0 or above'
+
+        # determine efficient attention configs for cuda and cpu
+
+        self.cpu_config = AttentionConfig(True, True, True)
+        self.cuda_config = None
+
+        if not torch.cuda.is_available() or not flash:
+            return
+
+        device_properties = torch.cuda.get_device_properties(torch.device('cuda'))
+
+        if device_properties.major == 8 and device_properties.minor == 0:
+            print_once('A100 GPU detected, using flash attention if input tensor is on cuda')
+            self.cuda_config = AttentionConfig(True, False, False)
+        else:
+            print_once('Non-A100 GPU detected, using math or mem efficient attention if input tensor is on cuda')
+            self.cuda_config = AttentionConfig(False, True, True)
+
+    def flash_attn(self, q, k, v):
+        _, heads, q_len, _, k_len, is_cuda = *q.shape, k.shape[-2], q.is_cuda
+
+        q, k, v = map(lambda t: t.contiguous(), (q, k, v))
+
+        # Check if there is a compatible device for flash attention
+
+        config = self.cuda_config if is_cuda else self.cpu_config
+
+        # pytorch 2.0 flash attn: q, k, v, mask, dropout, causal, softmax_scale
+
+        with torch.backends.cuda.sdp_kernel(**config._asdict()):
+            out = F.scaled_dot_product_attention(
+                q, k, v,
+                dropout_p = self.dropout if self.training else 0.
+            )
+
+        return out
+
+    def forward(self, q, k, v, bias = None):
+        """
+        einstein notation
+        b - batch
+        h - heads
+        n, i, j - sequence length (base sequence length, source, target)
+        d - feature dimension
+        """
+
+        q_len, k_len, device = q.shape[-2], k.shape[-2], q.device
+
+        if self.flash:
+            assert not exists(bias)
+            return self.flash_attn(q, k, v)
+
+        scale = q.shape[-1] ** -0.5
+
+        # similarity
+
+        sim = einsum(f"b h i d, b h j d -> b h i j", q, k) * scale
+
+        # attention
+
+        attn = sim.softmax(dim = -1)
+        attn = self.attn_dropout(attn)
+
+        # aggregate values
+
+        out = einsum(f"b h i j, b h j d -> b h i d", attn, v)
+
+        return out
diff --git a/make_a_video_pytorch/make_a_video.py b/make_a_video_pytorch/make_a_video.py
index b7bdb57..cf4ba49 100644
--- a/make_a_video_pytorch/make_a_video.py
+++ b/make_a_video_pytorch/make_a_video.py
@@ -9,6 +9,8 @@
 from einops import rearrange, repeat, pack, unpack
 from einops.layers.torch import Rearrange
 
+from make_a_video_pytorch.attend import Attend
+
 # helper functions
 
 def exists(val):
@@ -45,16 +47,17 @@ def forward(self, x):
 
 # layernorm 3d
 
-class ChanLayerNorm(nn.Module):
-    def __init__(self, dim):
+class RMSNorm(nn.Module):
+    def __init__(self, chan, dim = 1):
         super().__init__()
-        self.g = nn.Parameter(torch.ones(dim, 1, 1, 1))
+        self.dim = dim
+        self.gamma = nn.Parameter(torch.ones(chan))
 
     def forward(self, x):
-        eps = 1e-5 if x.dtype == torch.float32 else 1e-3
-        var = torch.var(x, dim = 1, unbiased = False, keepdim = True)
-        mean = torch.mean(x, dim = 1, keepdim = True)
-        return (x - mean) * var.clamp(min = eps).rsqrt() * self.g
+        dim = self.dim
+        right_ones = (dim + 1) if dim < 0 else (x.ndim - 1 - dim)
+        gamma = self.gamma.reshape(-1, *((1,) * right_ones))
+        return F.normalize(x, dim = dim) * (x.shape[dim] ** 0.5) * gamma
 
 # feedforward
 
@@ -79,7 +82,7 @@ def __init__(self, dim, mult = 4):
         )
 
         self.proj_out = nn.Sequential(
-            ChanLayerNorm(inner_dim),
+            RMSNorm(inner_dim),
             nn.Conv3d(inner_dim, dim, 1, bias = False)
         )
 
@@ -180,14 +183,17 @@ def __init__(
         self,
         dim,
         dim_head = 64,
-        heads = 8
+        heads = 8,
+        flash = False
     ):
         super().__init__()
         self.heads = heads
         self.scale = dim_head ** -0.5
         inner_dim = dim_head * heads
 
-        self.norm = nn.LayerNorm(dim)
+        self.attend = Attend(flash = flash)
+
+        self.norm = RMSNorm(dim, dim = -1)
 
         self.to_q = nn.Linear(dim, inner_dim, bias = False)
         self.to_kv = nn.Linear(dim, inner_dim * 2, bias = False)
@@ -200,23 +206,13 @@ def forward(
         x,
         rel_pos_bias = None
     ):
-
         x = self.norm(x)
 
         q, k, v = self.to_q(x), *self.to_kv(x).chunk(2, dim = -1)
 
         q, k, v = map(lambda t: rearrange(t, 'b n (h d) -> b h n d', h = self.heads), (q, k, v))
 
-        q = q * self.scale
-
-        sim = einsum('b h i d, b h j d -> b h i j', q, k)
-
-        if exists(rel_pos_bias):
-            sim = sim + rel_pos_bias
-
-        attn = sim.softmax(dim = -1)
-
-        out = einsum('b h i j, b h j d -> b h i d', attn, v)
+        out = self.attend(q, k, v, bias = rel_pos_bias)
 
         out = rearrange(out, 'b h n d -> b n (h d)')
         return self.to_out(out)
@@ -283,14 +279,18 @@ def __init__(
         dim_head = 64,
         heads = 8,
         add_feed_forward = True,
-        ff_mult = 4
+        ff_mult = 4,
+        pos_bias = True,
+        flash = False
     ):
         super().__init__()
-        self.spatial_attn = Attention(dim = dim, dim_head = dim_head, heads = heads)
-        self.spatial_rel_pos_bias = ContinuousPositionBias(dim = dim // 2, heads = heads, num_dims = 2)
+        assert not (flash and pos_bias), 'learned positional attention bias is not compatible with flash attention'
+
+        self.spatial_attn = Attention(dim = dim, dim_head = dim_head, heads = heads, flash = flash)
+        self.spatial_rel_pos_bias = ContinuousPositionBias(dim = dim // 2, heads = heads, num_dims = 2) if pos_bias else None
 
-        self.temporal_attn = Attention(dim = dim, dim_head = dim_head, heads = heads)
-        self.temporal_rel_pos_bias = ContinuousPositionBias(dim = dim // 2, heads = heads, num_dims = 1)
+        self.temporal_attn = Attention(dim = dim, dim_head = dim_head, heads = heads, flash = flash)
+        self.temporal_rel_pos_bias = ContinuousPositionBias(dim = dim // 2, heads = heads, num_dims = 1) if pos_bias else None
 
         self.has_feed_forward = add_feed_forward
         if not add_feed_forward:
@@ -312,7 +312,7 @@ def forward(
         else:
             x = rearrange(x, 'b c h w -> b (h w) c')
 
-        space_rel_pos_bias = self.spatial_rel_pos_bias(h, w)
+        space_rel_pos_bias = self.spatial_rel_pos_bias(h, w) if exists(self.spatial_rel_pos_bias) else None
 
         x = self.spatial_attn(x, rel_pos_bias = space_rel_pos_bias) + x
 
@@ -325,7 +325,7 @@ def forward(
 
             x = rearrange(x, 'b c f h w -> (b h w) f c')
 
-            time_rel_pos_bias = self.temporal_rel_pos_bias(x.shape[1])
+            time_rel_pos_bias = self.temporal_rel_pos_bias(x.shape[1]) if exists(self.temporal_rel_pos_bias) else None
 
             x = self.temporal_attn(x, rel_pos_bias = time_rel_pos_bias) + x
 
@@ -543,7 +543,9 @@ def __init__(
         resnet_block_depths = (2, 2, 2, 2),
         attn_dim_head = 64,
         attn_heads = 8,
-        condition_on_timestep = True
+        condition_on_timestep = True,
+        attn_pos_bias = True,
+        flash_attn = False
     ):
         super().__init__()
         assert len(dim_mult) == len(self_attns) == len(temporal_compression) == len(resnet_block_depths)
@@ -576,13 +578,15 @@ def __init__(
 
         attn_kwargs = dict(
             dim_head = attn_dim_head,
-            heads = attn_heads
+            heads = attn_heads,
+            pos_bias = attn_pos_bias,
+            flash= flash_attn
         )
 
         mid_dim = dims[-1]
 
         self.mid_block1 = ResnetBlock(mid_dim, mid_dim, timestep_cond_dim = timestep_cond_dim)
-        self.mid_attn = SpatioTemporalAttention(dim = mid_dim)
+        self.mid_attn = SpatioTemporalAttention(dim = mid_dim, **attn_kwargs)
         self.mid_block2 = ResnetBlock(mid_dim, mid_dim, timestep_cond_dim = timestep_cond_dim)
 
         for _, self_attend, (dim_in, dim_out), compress_time, resnet_block_depth in zip(range(num_layers), self_attns, dim_in_out, temporal_compression, resnet_block_depths):
diff --git a/setup.py b/setup.py
index 412dbb2..ae9c875 100644
--- a/setup.py
+++ b/setup.py
@@ -3,7 +3,7 @@
 setup(
   name = 'make-a-video-pytorch',
   packages = find_packages(exclude=[]),
-  version = '0.2.1',
+  version = '0.3.0',
   license='MIT',
   description = 'Make-A-Video - Pytorch',
   author = 'Phil Wang',