diff --git a/miles/rollout/rm_hub/__init__.py b/miles/rollout/rm_hub/__init__.py
index 29bebd78af..b6135b947a 100644
--- a/miles/rollout/rm_hub/__init__.py
+++ b/miles/rollout/rm_hub/__init__.py
@@ -6,8 +6,6 @@
 from miles.utils.misc import load_function
 from miles.utils.types import Sample
 
-from .ocr import ocr_rm
-
 
 def _resolve_rm_type(args, sample: Sample) -> str:
     metadata = sample.metadata if isinstance(sample.metadata, dict) else {}
@@ -38,7 +36,13 @@ async def async_rm(args, sample: Sample, **kwargs):
     elif rm_type == "random":
         return random.randint(0, 1)
     elif rm_type == "ocr":
+        from .ocr import ocr_rm
+
         return await ocr_rm(args, sample)
+    elif rm_type == "hps":
+        from .hps import hps_rm
+
+        return (await hps_rm(args, [sample]))[0]
     elif rm_type:
         raise NotImplementedError(f"Rule-based RM for {rm_type} is not implemented.")
     else:
@@ -55,6 +59,11 @@ async def batched_async_rm(
         rm_function = load_function(args.custom_rm_path)
         return await rm_function(args, samples, **kwargs)
 
+    if samples and all(_resolve_rm_type(args, sample) == "hps" for sample in samples):
+        from .hps import hps_rm
+
+        return await hps_rm(args, samples)
+
     tasks = [async_rm(args, sample, **kwargs) for sample in samples]
     rewards = await asyncio.gather(*tasks)
     return rewards
diff --git a/miles/rollout/rm_hub/hps.py b/miles/rollout/rm_hub/hps.py
new file mode 100644
index 0000000000..d082a558aa
--- /dev/null
+++ b/miles/rollout/rm_hub/hps.py
@@ -0,0 +1,186 @@
+from __future__ import annotations
+
+import asyncio
+import logging
+from collections.abc import Sequence
+
+import numpy as np
+import ray
+import torch
+from PIL import Image
+
+from miles.utils.misc import SingletonMeta
+from miles.utils.types import Sample
+
+logger = logging.getLogger(__name__)
+
+
+def _sample_to_rgb_hwc_uint8(sample: Sample) -> np.ndarray:
+    t = sample.generated_output
+    if t is None:
+        raise ValueError("generated_output is None")
+    if t.ndim != 4:
+        raise ValueError(f"generated_output must be 4D [C, F, H, W], got {tuple(t.shape)}")
+
+    frame_chw = t.detach().cpu()[:, 0, :, :]
+    hwc = frame_chw.float().numpy().transpose(1, 2, 0)
+    if float(hwc.max()) <= 1.0 + 1e-3:
+        hwc = np.round(hwc * 255.0)
+    return np.ascontiguousarray(hwc.clip(0, 255).astype(np.uint8))
+
+
+class HPSScorer(torch.nn.Module):
+    """HPS / HPSv2.1 reward scorer.
+
+    Loads the ViT-H-14 backbone via hpsv2's own ``create_model_and_transforms``
+    (so the preprocessing pipeline matches the published checkpoint exactly),
+    then patches in the HPS preference-tuned weights. Scoring returns the raw
+    image/text logit diagonal — the same scalar hpsv2.score() returns.
+    """
+
+    def __init__(
+        self,
+        *,
+        device: str = "cuda",
+        hps_version: str = "v2.1",
+        checkpoint_path: str | None = None,
+    ) -> None:
+        super().__init__()
+        import huggingface_hub
+        from hpsv2.src.open_clip import create_model_and_transforms, get_tokenizer
+        from hpsv2.utils import hps_version_map
+
+        self.device = torch.device(device)
+        self.hps_version = hps_version
+
+        model, _, preprocess_val = create_model_and_transforms(
+            "ViT-H-14",
+            "laion2B-s32B-b79K",
+            precision="amp",
+            device=str(self.device),
+            jit=False,
+            force_quick_gelu=False,
+            force_custom_text=False,
+            force_patch_dropout=False,
+            force_image_size=None,
+            pretrained_image=False,
+            image_mean=None,
+            image_std=None,
+            light_augmentation=True,
+            aug_cfg={},
+            output_dict=True,
+            with_score_predictor=False,
+            with_region_predictor=False,
+        )
+
+        if checkpoint_path is None:
+            checkpoint_path = huggingface_hub.hf_hub_download(
+                "xswu/HPSv2", hps_version_map[hps_version]
+            )
+        checkpoint = torch.load(checkpoint_path, map_location=str(self.device))
+        model.load_state_dict(checkpoint["state_dict"])
+        model.to(self.device).eval()
+
+        self.model = model
+        self.preprocess = preprocess_val
+        self.tokenizer = get_tokenizer("ViT-H-14")
+
+    @torch.no_grad()
+    def forward(self, prompts: Sequence[str], images: Sequence[Image.Image]) -> list[float]:
+        if not prompts:
+            return []
+
+        image_batch = torch.stack([self.preprocess(img) for img in images]).to(
+            self.device, non_blocking=True
+        )
+        text_batch = self.tokenizer(list(prompts)).to(self.device, non_blocking=True)
+
+        with torch.amp.autocast(self.device.type, enabled=self.device.type == "cuda"):
+            outputs = self.model(image_batch, text_batch)
+            image_features = outputs["image_features"]
+            text_features = outputs["text_features"]
+            logits = image_features @ text_features.T
+            scores = torch.diagonal(logits)
+
+        return [float(score) for score in scores.detach().float().cpu()]
+
+
+@ray.remote
+class HPSRewardActor:
+    def __init__(
+        self,
+        *,
+        hps_version: str,
+        checkpoint_path: str | None = None,
+    ) -> None:
+        use_cuda = bool(ray.get_gpu_ids()) and torch.cuda.is_available()
+        if use_cuda:
+            torch.cuda.set_device(0)
+        device = "cuda" if use_cuda else "cpu"
+        self.scorer = HPSScorer(
+            device=device,
+            hps_version=hps_version,
+            checkpoint_path=checkpoint_path,
+        )
+
+    def score_batch(self, images: list[np.ndarray], prompts: list[str]) -> list[float]:
+        pil_images = [Image.fromarray(image) for image in images]
+        return self.scorer(prompts, pil_images)
+
+
+class AsyncHPSPool(metaclass=SingletonMeta):
+    """Ray actor pool for GPU HPS reward inference."""
+
+    def __init__(self, args) -> None:
+        num_workers = args.hps_num_workers
+        num_gpus_per_worker = args.hps_num_gpus_per_worker
+        if num_workers <= 0:
+            raise ValueError("--hps-num-workers must be positive")
+        if args.hps_batch_size <= 0:
+            raise ValueError("--hps-batch-size must be positive")
+
+        self._batch_size = args.hps_batch_size
+        self._actors = [
+            HPSRewardActor.options(
+                num_cpus=1,
+                num_gpus=num_gpus_per_worker,
+                scheduling_strategy="DEFAULT",
+            ).remote(
+                hps_version=args.hps_version,
+                checkpoint_path=args.hps_checkpoint_path,
+            )
+            for _ in range(num_workers)
+        ]
+        self._round_robin_index = 0
+        logger.info(
+            "Initialized HPS actor pool with %d workers, %.3f GPUs/worker, batch_size=%d, version=%s.",
+            num_workers,
+            num_gpus_per_worker,
+            self._batch_size,
+            args.hps_version,
+        )
+
+    def _next_actor(self):
+        i = self._round_robin_index % len(self._actors)
+        self._round_robin_index += 1
+        return self._actors[i]
+
+    async def score(self, images: list[np.ndarray], prompts: list[str]) -> list[float]:
+        if not images:
+            return []
+
+        refs = []
+        for start in range(0, len(images), self._batch_size):
+            end = start + self._batch_size
+            refs.append(self._next_actor().score_batch.remote(images[start:end], prompts[start:end]))
+
+        loop = asyncio.get_running_loop()
+        chunked_scores = await loop.run_in_executor(None, ray.get, refs)
+        return [float(score) for chunk in chunked_scores for score in chunk]
+
+
+async def hps_rm(args, samples: Sequence[Sample]) -> list[float]:
+    pool = AsyncHPSPool(args)
+    images = [_sample_to_rgb_hwc_uint8(sample) for sample in samples]
+    prompts = [sample.prompt for sample in samples]
+    return await pool.score(images, prompts)
diff --git a/miles/utils/arguments.py b/miles/utils/arguments.py
index a23264eafd..838fb416e3 100644
--- a/miles/utils/arguments.py
+++ b/miles/utils/arguments.py
@@ -1402,6 +1402,37 @@ def add_reward_model_arguments(parser):
                 default=4,
                 help="Number of Ray OCR actors used when --rm-type ocr.",
             )
+            parser.add_argument(
+                "--hps-num-workers",
+                type=int,
+                default=1,
+                help="Number of Ray HPS actors used when --rm-type hps.",
+            )
+            parser.add_argument(
+                "--hps-num-gpus-per-worker",
+                type=float,
+                default=1.0,
+                help="GPU resources per HPS actor. Use 1.0 for a dedicated GPU smoke test.",
+            )
+            parser.add_argument(
+                "--hps-batch-size",
+                type=int,
+                default=8,
+                help="Batch size per HPS actor call.",
+            )
+            parser.add_argument(
+                "--hps-version",
+                type=str,
+                default="v2.1",
+                choices=["v2.0", "v2.1"],
+                help="HPS checkpoint version to use when --rm-type hps.",
+            )
+            parser.add_argument(
+                "--hps-checkpoint-path",
+                type=str,
+                default=None,
+                help="Optional local HPS checkpoint path. If unset, the checkpoint is downloaded from Hugging Face.",
+            )
             parser.add_argument(
                 "--custom-rm-path",
                 type=str,
diff --git a/requirements.txt b/requirements.txt
index 6a7c1809c6..d5f9fd15df 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,7 @@
 accelerate
 blobfile
 datasets
+hpsv2
 httpx[http2]
 mcp[cli]
 memray  # needed for debugging (but is lightweight), we can put it to dev mode when using pyproject.toml
diff --git a/scripts/run-diffusion-grpo-hps-smoke.sh b/scripts/run-diffusion-grpo-hps-smoke.sh
new file mode 100755
index 0000000000..5c53a653fc
--- /dev/null
+++ b/scripts/run-diffusion-grpo-hps-smoke.sh
@@ -0,0 +1,97 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+PYTHON_BIN="${PYTHON_BIN:-/usr/bin/python3}"
+
+SMOKE_COLOCATE="${SMOKE_COLOCATE:-1}"
+SMOKE_ACTOR_GPUS_PER_NODE="${SMOKE_ACTOR_GPUS_PER_NODE:-2}"
+SMOKE_ROLLOUT_GPUS="${SMOKE_ROLLOUT_GPUS:-2}"
+SMOKE_ROLLOUT_GPUS_PER_ENGINE="${SMOKE_ROLLOUT_GPUS_PER_ENGINE:-1}"
+SMOKE_HPS_VERSION="${SMOKE_HPS_VERSION:-v2.1}"
+SMOKE_HPS_NUM_WORKERS="${SMOKE_HPS_NUM_WORKERS:-1}"
+SMOKE_HPS_BATCH_SIZE="${SMOKE_HPS_BATCH_SIZE:-8}"
+
+COLOCATE_ARGS=()
+if [[ "${SMOKE_COLOCATE}" == "1" || "${SMOKE_COLOCATE}" == "true" || "${SMOKE_COLOCATE}" == "yes" ]]; then
+  # Use two colocated train/rollout GPUs plus one dedicated HPS reward GPU.
+  DEFAULT_CUDA_VISIBLE_DEVICES="4,5,6"
+  DEFAULT_NUM_GPUS_PER_NODE="3"
+  COLOCATE_ARGS+=(--colocate)
+else
+  # Use two train GPUs, two rollout GPUs, and one dedicated HPS reward GPU.
+  DEFAULT_CUDA_VISIBLE_DEVICES="1,2,3,4,5"
+  DEFAULT_NUM_GPUS_PER_NODE="5"
+fi
+
+SMOKE_NUM_GPUS_PER_NODE="${SMOKE_NUM_GPUS_PER_NODE:-${DEFAULT_NUM_GPUS_PER_NODE}}"
+
+export CUDA_VISIBLE_DEVICES="${CUDA_VISIBLE_DEVICES:-${DEFAULT_CUDA_VISIBLE_DEVICES}}"
+export PYTORCH_CUDA_ALLOC_CONF="${PYTORCH_CUDA_ALLOC_CONF:-expandable_segments:True}"
+
+RUN_NAME="diffusion_grpo_hps_smoke_$(date +%Y%m%d_%H%M%S)"
+
+WANDB_ARGS=()
+if [[ -n "${WANDB_API_KEY:-}" ]]; then
+  WANDB_ARGS+=(
+    --use-wandb
+    --wandb-project miles-diffusion-grpo
+    --wandb-group "${RUN_NAME}"
+    --wandb-key "${WANDB_API_KEY}"
+    --diffusion-log-images 4
+    --diffusion-log-image-interval 1
+    --disable-wandb-random-suffix
+  )
+fi
+
+"${PYTHON_BIN}" "${ROOT_DIR}/tools/prepare_ocr_jsonl.py"
+
+"${PYTHON_BIN}" -u "${ROOT_DIR}/train_diffusion.py" \
+  --train-backend fsdp \
+  --diffusion-train \
+  --rollout-function-path miles.rollout.sglang_diffusion_rollout.generate_rollout \
+  --hf-checkpoint gpt2 \
+  --prompt-data "${ROOT_DIR}/data/ocr/train.jsonl" \
+  --input-key input \
+  --rollout-batch-size 1 \
+  --n-samples-per-prompt 2 \
+  --num-rollout 1 \
+  --diffusion-timestep-batch 10 \
+  --gradient-checkpointing \
+  --actor-num-gpus-per-node "${SMOKE_ACTOR_GPUS_PER_NODE}" \
+  --rollout-num-gpus "${SMOKE_ROLLOUT_GPUS}" \
+  --rollout-num-gpus-per-engine "${SMOKE_ROLLOUT_GPUS_PER_ENGINE}" \
+  --num-gpus-per-node "${SMOKE_NUM_GPUS_PER_NODE}" \
+  "${COLOCATE_ARGS[@]}" \
+  --no-offload-rollout \
+  --use-lora \
+  --lora-rank 64 \
+  --lora-alpha 128 \
+  --diffusion-init-lora-weight gaussian \
+  --use-miles-router \
+  --sglang-server-concurrency 2 \
+  --diffusion-model Qwen/Qwen-Image \
+  --diffusion-reward hps:1.0 \
+  --advantage-estimator grpo \
+  --globalize-reward-std \
+  --rm-type hps \
+  --hps-version "${SMOKE_HPS_VERSION}" \
+  --hps-num-workers "${SMOKE_HPS_NUM_WORKERS}" \
+  --hps-num-gpus-per-worker 1 \
+  --hps-batch-size "${SMOKE_HPS_BATCH_SIZE}" \
+  --diffusion-dtype bf16 \
+  --diffusion-num-steps 10 \
+  --diffusion-guidance-scale 4.0 \
+  --diffusion-true-cfg-scale 4.0 \
+  --diffusion-noise-level 1.2 \
+  --diffusion-step-strategy-path miles.rollout.step_strategy_hub.sde_window \
+  --diffusion-sde-window-size 2 \
+  --diffusion-sde-window-range 0,5 \
+  --diffusion-height 256 \
+  --diffusion-width 256 \
+  --global-batch-size 2 \
+  --diffusion-ignore-last 1 \
+  --diffusion-debug-mode \
+  --debug-skip-optimizer-step \
+  "${WANDB_ARGS[@]}"