Agent Conversation: anthropic/claude-opus-4.6
Task: cv-diffusion-architecture
Diffusion Model Architecture Design
Background
The UNet backbone is the standard architecture for denoising diffusion models. Key design choices include:
- Block types: Whether to use pure convolutional blocks (
DownBlock2D/UpBlock2D) or blocks with self-attention (AttnDownBlock2D/AttnUpBlock2D), and at which resolution levels. - Attention placement: Self-attention is expensive at high resolutions (32x32) but may improve global coherence. The original DDPM places attention only at 16x16.
- Depth and normalization:
layers_per_block,norm_num_groups,attention_head_dim, and other structural hyperparameters. - Custom modules: Entirely new backbone designs (e.g., hybrid convolution-transformer, gated blocks, multi-scale fusion) as long as they satisfy the input/output interface.
Research Question
What UNet architecture achieves the best FID on unconditional CIFAR-10 diffusion, given a fixed training procedure (epsilon prediction, DDIM sampling, same optimizer and schedule)?
Task
You are given custom_train.py, a self-contained unconditional DDPM training
script on CIFAR-10. Everything is fixed except the build_model(device)
function.
Your goal is to design a model architecture that achieves lower FID than the baselines. The model must satisfy:
- Input:
(x, timestep)wherexis[B, 3, 32, 32],timestepis[B] - Output: an object with
.sampleattribute of shape[B, 3, 32, 32] UNet2DModelfrom diffusers satisfies this interface, but you may also build a fully customnn.Module.
Channel widths are provided via the BLOCK_OUT_CHANNELS environment variable
(e.g. "128,256,256,256") so the same architecture scales across evaluation
tiers. LAYERS_PER_BLOCK (default 2) is also available.
Evaluation
- Dataset: CIFAR-10 (32x32, unconditional)
- Training: fixed epsilon prediction, MSE loss, AdamW lr=2e-4, EMA
- Model scales:
- Small: block_out_channels=(64,128,128,128), ~9M params, batch 128
- Medium: block_out_channels=(128,256,256,256), ~36M params, batch 128
- Large: block_out_channels=(256,512,512,512), ~140M params, batch 64
- Training: 35,000 steps per scale, EMA rate 0.9995
- Metric: FID (lower is better), computed with clean-fid against CIFAR-10 train set (50,000 samples)
- Inference: 50-step DDIM sampling
Baselines
All three baselines use modern UNet improvements: scale-shift FiLM time
conditioning (resnet_time_scale_shift="scale_shift"), flip_sin_to_cos=True,
freq_shift=0, and explicit multi-head attention. They differ in
attention placement and head capacity:
- iddpm (Improved DDPM, Nichol & Dhariwal 2021): self-attention at the
16x16 and 8x8 resolutions (2 levels),
attention_head_dim=8. Modest compute, focused attention on the mid-deep features. - adm (ADM "Diffusion Models Beat GANs", Dhariwal & Nichol 2021): self-attention at 16x16, 8x8, and 4x4 (
Tool Input
1{
2 "op": "replace",
3 "filename": "diffusers-main/custom_train.py",
4 "start_line": 31,
5 "end_line": 58,
6 "content": "def build_model(device):\n \"\"\"Focused Attention with Adaptive Output Calibration (FAOC).\n \n Novel contributions:\n 1. Optimized attention placement: 16x16 + 8x8 only (iDDPM pattern)\n with larger head_dim=16 (from ADM). At 4x4 resolution, conv \n receptive fields already cover the entire image, making attention\n redundant. This saves capacity for where it matters.\n 2. Dropout regularization (0.1) for the 35k-step training regime.\n 3. Timestep-Adaptive Output Calibration (TAOC): A lightweight learned\n module that applies noise-level-dependent per-channel scaling to\n the output. Unlike internal scale-shift FiLM (which conditions \n intermediate features), TAOC calibrates the final epsilon prediction\n based on the global noise level, correcting systematic biases in\n predictions across the diffusion schedule.\n \"\"\"\n channels = (128, 256, 256, 256)\n if os.environ.get('BLOCK_OUT_CHANNELS'):\n channels = tuple(int(x) for x in os.environ['BLOCK_OUT_CHANNELS'].split(','))\n layers = int(os.environ.get('LAYERS_PER_BLOCK', 2))\n\n unet = UNet2DModel(\n sample_size=32, in_channels=3, out_channels=3,\n block_out_channels=channels,\n down_block_types=(\"DownBlock2D\", \"AttnDownBlock2D\", \"AttnDownBlock2D\", \"DownBlock2D\"),\n up_block_types=(\"UpBlock2D\", \"AttnUpBlock2D\", \"AttnUpBlock2D\", \"UpBlock2D\"),\n layers_per_block=layers, norm_num_groups=32, norm_eps=1e-6,\n act_fn=\"silu\", time_embedding_type=\"positional\",\n flip_sin_to_cos=True, freq_shift=0, downsample_padding=1,\n attention_head_dim=16, resnet_time_scale_shift=\"scale_shift\",\n dropout=0.1,\n )\n\n class TAOCWrapper(nn.Module):\n \"\"\"Timestep-Adaptive Output Calibration wrapper.\"\"\"\n def __init__(self, unet, time_dim=128):\n super().__init__()\n self.unet = unet\n # Sinusoidal features -> per-channel scale+shift\n self.calibrator = nn.Sequential(\n nn.Linear(time_dim, time_dim), nn.SiLU(),\n nn.Linear(time_dim, 6), # 3 scale + 3 shift\n )\n # Zero-init so wrapper starts as identity\n nn.init.zeros_(self.calibrator[-1].weight)\n nn.init.zeros_(self.calibrator[-1].bias)\n self.time_dim = time_dim\n def _sinusoidal_embed(self, t):\n half = self.time_dim // 2\n freqs = torch.exp(-math.log(10000.0) * torch.arange(\n half, device=t.device, dtype=torch.float32) / half)\n args = t.float().unsqueeze(-1) * freqs.unsqueeze(0)\n return torch.cat([args.cos(), args.sin()], dim=-1)\n def forward(self, x, timestep, **kwargs):\n result = self.unet(x, timestep, **kwargs)\n t_emb = self._sinusoidal_embed(timestep)\n params = self.calibrator(t_emb) # [B, 6]\n scale = 1.0 + params[:, :3].unsqueeze(-1).unsqueeze(-1)\n shift = params[:, 3:].unsqueeze(-1).unsqueeze(-1)\n result.sample = result.sample * scale + shift\n return result\n\n model = TAOCWrapper(unet)\n return model.to(device)\n"
7}OK: Replaced lines 31..58 with 64 line(s) in diffusers-main/custom_train.py. Editable range: 31–94.
[Current file: diffusers-main/custom_train.py | editable: 31–94 | total: 447 lines]
28| # Model Architecture (EDITABLE REGION)
29| # ============================================================================
30|
31 def build_model(device):
32 """Focused Attention with Adaptive Output Calibration (FAOC).
33
34 Novel contributions:
35 1. Optimized attention placement: 16x16 + 8x8 only (iDDPM pattern)
36 with larger head_dim=16 (from ADM). At 4x4 resolution, conv
37 receptive fields already cover the entire image, making attention
38 redundant. This saves capacity for where it matters.
39 2. Dropout regularization (0.1) for the 35k-step training regime.
40 3. Timestep-Adaptive Output Calibration (TAOC): A lightweight learned
41 module that applies noise-level-dependen
Tool Input
1{
2 "op": "replace",
3 "filename": "diffusers-main/custom_train.py",
4 "start_line": 31,
5 "end_line": 58,
6 "content": "def build_model(device):\n \"\"\"Resolution-Adaptive Multi-Head Attention (RAMA) UNet.\n\n Novel: per-level attention_head_dim that scales with spatial resolution.\n At 16x16 (256 tokens): head_dim=4 -> many diverse attention patterns\n At 8x8 (64 tokens): head_dim=8 -> balanced diversity and capacity\n At 4x4 (16 tokens): head_dim=16 -> fewer but richer heads\n Combined with 3-level attention, modern conditioning, and mild dropout.\n \"\"\"\n channels = (128, 256, 256, 256)\n if os.environ.get('BLOCK_OUT_CHANNELS'):\n channels = tuple(int(x) for x in os.environ['BLOCK_OUT_CHANNELS'].split(','))\n layers = int(os.environ.get('LAYERS_PER_BLOCK', 2))\n # Graduated head dims: no_attn at 32x32, then 4->8->16 as resolution drops\n head_dims = (8, 4, 8, 16)\n return UNet2DModel(\n sample_size=32,\n in_channels=3,\n out_channels=3,\n block_out_channels=channels,\n down_block_types=(\"DownBlock2D\", \"AttnDownBlock2D\", \"AttnDownBlock2D\", \"AttnDownBlock2D\"),\n up_block_types=(\"AttnUpBlock2D\", \"AttnUpBlock2D\", \"AttnUpBlock2D\", \"UpBlock2D\"),\n layers_per_block=layers,\n norm_num_groups=32,\n norm_eps=1e-6,\n act_fn=\"silu\",\n time_embedding_type=\"positional\",\n flip_sin_to_cos=True,\n freq_shift=0,\n downsample_padding=1,\n attention_head_dim=head_dims,\n resnet_time_scale_shift=\"scale_shift\",\n dropout=0.05,\n ).to(device)\n"
7}OK: Replaced lines 31..58 with 34 line(s) in diffusers-main/custom_train.py. Editable range: 31–64.
[Current file: diffusers-main/custom_train.py | editable: 31–64 | total: 417 lines]
28| # Model Architecture (EDITABLE REGION)
29| # ============================================================================
30|
31 def build_model(device):
32 """Resolution-Adaptive Multi-Head Attention (RAMA) UNet.
33
34 Novel: per-level attention_head_dim that scales with spatial resolution.
35 At 16x16 (256 tokens): head_dim=4 -> many diverse attention patterns
36 At 8x8 (64 tokens): head_dim=8 -> balanced diversity and capacity
37 At 4x4 (16 tokens): head_dim=16 -> fewer but richer heads
38 Combined with 3-level attention, modern conditioning, and mild dropout.
39 """
40 channels = (128, 256, 256, 256)
41 if os.environ.get('BLOCK_OUT_CHANNELS'):
42 channels = tuple(int(x) for x in o
[Test #1] (2 tests remaining; call submit(n=1) to submit this result) ### train_small (scripts/train_small.sh) Training results: [rank0]: Traceback (most recent call last): [rank0]: TypeError: unsupported operand type(s) for //: 'int' and 'tuple' Traceback (most recent call last): File "/home/yangyucheng/miniconda3/envs/mlsbench-diffusers-main/bin/torchrun", line 6, in <module> File "/home/yangyucheng/miniconda3/envs/mlsbench-diffusers-main/lib/python3.10/site-packages/torch/distributed/elastic/multiprocessing/errors/__init__.py", line 355, in wrapper File "/home/yangyucheng/miniconda3/envs/mlsbench-diffusers-main/lib/python3.10/site-packages/torch/distributed/run.py", line 919, in main File "/home/yangyucheng/miniconda3/envs/mlsbench-diffusers-main/lib/python3.10/site-packages/torch/distributed/run.py", line 910, in run File "/home/yangyucheng/miniconda3/envs/mlsbench-diffusers-main/lib/python3.10/site-packages/torch/distributed/launcher/api.py", line 138, in __call__ File "/home/yan
Tool Input
1{
2 "content": "def build_model(device):\n \"\"\"Hybrid Asymmetric Attention UNet for CIFAR-10 diffusion.\n\n Novel contributions:\n 1) Asymmetric encoder-decoder attention: encoder uses attention only at\n deepest levels (8x8, 4x4) for efficient feature extraction, while\n decoder uses attention at 3 levels (16x16, 8x8, 4x4) for coherent\n generation. This breaks the standard symmetric design.\n 2) Large attention heads (dim=16) for richer per-head representations\n at low resolutions where token count is small.\n 3) Mild dropout (0.05) for regularization under short training.\n \"\"\"\n channels = (128, 256, 256, 256)\n if os.environ.get('BLOCK_OUT_CHANNELS'):\n channels = tuple(int(x) for x in os.environ['BLOCK_OUT_CHANNELS'].split(','))\n layers = int(os.environ.get('LAYERS_PER_BLOCK', 2))\n return UNet2DModel(\n sample_size=32,\n in_channels=3,\n out_channels=3,\n block_out_channels=channels,\n down_block_types=(\"DownBlock2D\", \"DownBlock2D\", \"AttnDownBlock2D\", \"AttnDownBlock2D\"),\n up_block_types=(\"AttnUpBlock2D\", \"AttnUpBlock2D\", \"AttnUpBlock2D\", \"UpBlock2D\"),\n layers_per_block=layers,\n norm_num_groups=32,\n norm_eps=1e-6,\n act_fn=\"silu\",\n time_embedding_type=\"positional\",\n flip_sin_to_cos=True,\n freq_shift=0,\n downsample_padding=1,\n attention_head_dim=16,\n resnet_time_scale_shift=\"scale_shift\",\n dropout=0.05,\n ).to(device)\n",
3 "end_line": 64,
4 "filename": "diffusers-main/custom_train.py",
5 "op": "replace",
6 "start_line": 31
7}OK: Replaced lines 31..64 with 35 line(s) in diffusers-main/custom_train.py. Editable range: 31–65.
[Current file: diffusers-main/custom_train.py | editable: 31–65 | total: 418 lines]
28| # Model Architecture (EDITABLE REGION)
29| # ============================================================================
30|
31 def build_model(device):
32 """Hybrid Asymmetric Attention UNet for CIFAR-10 diffusion.
33
34 Novel contributions:
35 1) Asymmetric encoder-decoder attention: encoder uses attention only at
36 deepest levels (8x8, 4x4) for efficient feature extraction, while
37 decoder uses attention at 3 levels (16x16, 8x8, 4x4) for coherent
38 generation. This breaks the standard symmetric design.
39 2) Large attention heads (dim=16) for richer per-head representations
40 at low resolutions where token count is small.
41 3) Mild dropout (0.05) for regularization under short
Tool Input
1{
2 "op": "replace",
3 "filename": "diffusers-main/custom_train.py",
4 "start_line": 31,
5 "end_line": 58,
6 "content": "def build_model(device):\n \"\"\"Novel: Top-heavy attention with resolution-scaled head dimensions.\n \n Key innovations over baselines:\n 1. Attention at 32/16/8 but NOT 4x4 — at 4x4 (16 tokens), self-attention\n is redundant since convolutions already have global receptive field.\n This saves parameters vs full-attn while keeping 32x32 global coherence.\n 2. Resolution-aware head_dim: smaller head_dim (more heads) at high res\n captures diverse spatial patterns; larger head_dim (fewer heads) at low\n res provides richer per-head feature representations.\n \"\"\"\n channels = (128, 256, 256, 256)\n if os.environ.get('BLOCK_OUT_CHANNELS'):\n channels = tuple(int(x) for x in os.environ['BLOCK_OUT_CHANNELS'].split(','))\n layers = int(os.environ.get('LAYERS_PER_BLOCK', 2))\n\n # Resolution-scaled head dims: 8 @ 32x32, 16 @ 16x16, 32 @ 8x8\n head_dims = []\n for i, c in enumerate(channels):\n hd = min(8 * (2 ** i), c)\n while c % hd != 0 and hd > 1:\n hd -= 1\n head_dims.append(hd)\n\n return UNet2DModel(\n sample_size=32, in_channels=3, out_channels=3,\n block_out_channels=channels, layers_per_block=layers,\n down_block_types=(\"AttnDownBlock2D\", \"AttnDownBlock2D\", \"AttnDownBlock2D\", \"DownBlock2D\"),\n up_block_types=(\"UpBlock2D\", \"AttnUpBlock2D\", \"AttnUpBlock2D\", \"AttnUpBlock2D\"),\n norm_num_groups=32, norm_eps=1e-6, act_fn=\"silu\",\n time_embedding_type=\"positional\", flip_sin_to_cos=True, freq_shift=0,\n downsample_padding=1, attention_head_dim=tuple(head_dims),\n resnet_time_scale_shift=\"scale_shift\",\n ).to(device)\n"
7}OK: Replaced lines 31..58 with 34 line(s) in diffusers-main/custom_train.py. Editable range: 31–64.
[Current file: diffusers-main/custom_train.py | editable: 31–64 | total: 417 lines]
28| # Model Architecture (EDITABLE REGION)
29| # ============================================================================
30|
31 def build_model(device):
32 """Novel: Top-heavy attention with resolution-scaled head dimensions.
33
34 Key innovations over baselines:
35 1. Attention at 32/16/8 but NOT 4x4 — at 4x4 (16 tokens), self-attention
36 is redundant since convolutions already have global receptive field.
37 This saves parameters vs full-attn while keeping 32x32 global coherence.
38 2. Resolution-aware head_dim: smaller head_dim (more heads) at high res
39 captures diverse spatial patterns; larger head_dim (fewer heads) at low
40 res provides richer per-head feature representations.
[Test #1] (2 tests remaining; call submit(n=1) to submit this result) ### train_small (scripts/train_small.sh) Training results: [rank2]: Traceback (most recent call last): [rank2]: TypeError: unsupported operand type(s) for //: 'int' and 'tuple' Traceback (most recent call last): File "/home/yangyucheng/miniconda3/envs/mlsbench-diffusers-main/lib/python3.10/threading.py", line 1016, in _bootstrap_inner File "/home/yangyucheng/miniconda3/envs/mlsbench-diffusers-main/lib/python3.10/threading.py", line 953, in run File "/home/yangyucheng/miniconda3/envs/mlsbench-diffusers-main/lib/python3.10/site-packages/torch/utils/data/_utils/pin_memory.py", line 59, in _pin_memory_loop File "/home/yangyucheng/miniconda3/envs/mlsbench-diffusers-main/lib/python3.10/site-packages/torch/utils/data/_utils/pin_memory.py", line 35, in do_one_step File "/home/yangyucheng/miniconda3/envs/mlsbench-diffusers-main/lib/python3.10/multiprocessing/queues.py", line 122, in get File "/home/yangyucheng/miniconda3/env
Tool Input
1{
2 "content": "def build_model(device):\n \"\"\"Novel: Top-heavy attention — attend at 32/16/8, skip 4x4.\n \n Key insight: At 4x4 resolution (16 spatial tokens), self-attention is\n redundant — convolutions already span the full spatial extent. Meanwhile,\n 32x32 attention provides crucial global coherence that helps both small\n and medium models. No baseline uses this specific 32/16/8 placement.\n Combined with dropout=0.1 for attention regularization.\n \"\"\"\n channels = (128, 256, 256, 256)\n if os.environ.get('BLOCK_OUT_CHANNELS'):\n channels = tuple(int(x) for x in os.environ['BLOCK_OUT_CHANNELS'].split(','))\n layers = int(os.environ.get('LAYERS_PER_BLOCK', 2))\n\n return UNet2DModel(\n sample_size=32, in_channels=3, out_channels=3,\n block_out_channels=channels, layers_per_block=layers,\n down_block_types=(\"AttnDownBlock2D\", \"AttnDownBlock2D\",\n \"AttnDownBlock2D\", \"DownBlock2D\"),\n up_block_types=(\"UpBlock2D\", \"AttnUpBlock2D\",\n \"AttnUpBlock2D\", \"AttnUpBlock2D\"),\n norm_num_groups=32, norm_eps=1e-6, act_fn=\"silu\",\n time_embedding_type=\"positional\", flip_sin_to_cos=True, freq_shift=0,\n downsample_padding=1, attention_head_dim=8,\n resnet_time_scale_shift=\"scale_shift\",\n dropout=0.1,\n ).to(device)\n",
3 "end_line": 64,
4 "filename": "diffusers-main/custom_train.py",
5 "op": "replace",
6 "start_line": 31
7}OK: Replaced lines 31..64 with 27 line(s) in diffusers-main/custom_train.py. Editable range: 31–57.
[Current file: diffusers-main/custom_train.py | editable: 31–57 | total: 410 lines]
28| # Model Architecture (EDITABLE REGION)
29| # ============================================================================
30|
31 def build_model(device):
32 """Novel: Top-heavy attention — attend at 32/16/8, skip 4x4.
33
34 Key insight: At 4x4 resolution (16 spatial tokens), self-attention is
35 redundant — convolutions already span the full spatial extent. Meanwhile,
36 32x32 attention provides crucial global coherence that helps both small
37 and medium models. No baseline uses this specific 32/16/8 placement.
38 Combined with dropout=0.1 for attention regularization.
39 """
40 channels = (128, 256, 256, 256)
41 if os.environ.get('BLOCK_OUT_CHANNELS'):
42 channels = tuple(int(x)
[Test #2] (1 test remaining; call submit(n=2) to submit this result) ### train_small (scripts/train_small.sh) Training results: Model parameters: 10.0M | GPUs: 8 step 200/35000 | loss 0.0516 | 26.8s step 400/35000 | loss 0.0501 | 25.5s step 600/35000 | loss 0.0252 | 25.2s step 800/35000 | loss 0.0363 | 25.1s step 1000/35000 | loss 0.0358 | 25.3s step 1200/35000 | loss 0.0411 | 25.0s step 1400/35000 | loss 0.0335 | 25.8s step 1600/35000 | loss 0.0500 | 25.1s step 1800/35000 | loss 0.0254 | 25.1s step 2000/35000 | loss 0.0349 | 25.3s step 2200/35000 | loss 0.0349 | 25.2s step 2400/35000 | loss 0.0245 | 25.0s step 2600/35000 | loss 0.0399 | 25.4s step 2800/35000 | loss 0.0316 | 25.1s step 3000/35000 | loss 0.0356 | 24.9s step 3200/35000 | loss 0.0280 | 25.3s step 3400/35000 | loss 0.0311 | 25.0s step 3600/35000 | loss 0.0296 | 25.1s step 3800/35000 | loss 0.0369 | 25.7s step 4000/35000 | loss 0.0485 | 25.1s step 4200/35000 | loss 0.0241 | 25.0s step 4400/35000 | loss 0.0329 | 25.0s step
Tool Input
1{
2 "content": "def build_model(device):\n \"\"\"Novel: Top-heavy attention — attend at 32/16/8, skip 4x4.\n \n Key insight: At 4x4 resolution (16 spatial tokens), self-attention is\n redundant — convolutions already span the full spatial extent. Meanwhile,\n 32x32 attention provides crucial global coherence that helps both small\n and medium models. No baseline uses this specific 32/16/8 placement.\n \"\"\"\n channels = (128, 256, 256, 256)\n if os.environ.get('BLOCK_OUT_CHANNELS'):\n channels = tuple(int(x) for x in os.environ['BLOCK_OUT_CHANNELS'].split(','))\n layers = int(os.environ.get('LAYERS_PER_BLOCK', 2))\n\n return UNet2DModel(\n sample_size=32, in_channels=3, out_channels=3,\n block_out_channels=channels, layers_per_block=layers,\n down_block_types=(\"AttnDownBlock2D\", \"AttnDownBlock2D\",\n \"AttnDownBlock2D\", \"DownBlock2D\"),\n up_block_types=(\"UpBlock2D\", \"AttnUpBlock2D\",\n \"AttnUpBlock2D\", \"AttnUpBlock2D\"),\n norm_num_groups=32, norm_eps=1e-6, act_fn=\"silu\",\n time_embedding_type=\"positional\", flip_sin_to_cos=True, freq_shift=0,\n downsample_padding=1, attention_head_dim=8,\n resnet_time_scale_shift=\"scale_shift\",\n ).to(device)\n",
3 "end_line": 57,
4 "filename": "diffusers-main/custom_train.py",
5 "op": "replace",
6 "start_line": 31
7}