diff --git a/train_mnist_demo.py b/train_mnist_demo.py
new file mode 100644
index 0000000..dc37475
--- /dev/null
+++ b/train_mnist_demo.py
@@ -0,0 +1,163 @@
+import argparse
+import hashlib
+import random
+from dataclasses import dataclass
+
+import numpy as np
+import torch
+from torch import nn
+from torch.utils.data import DataLoader
+from torchvision import datasets, transforms
+
+
+# ------------------------- Seeding utilities -------------------------
+
+def make_subseed(master_seed: int, component_id: str, run_id: str, stream_id=0) -> int:
+    """Derive a deterministic subseed from identifiers.
+
+    Uses SHA256 to hash the identifiers and returns a 64-bit integer.
+    """
+    payload = f"{master_seed}|{component_id}|{run_id}|{stream_id}".encode()
+    digest = hashlib.sha256(payload).digest()[:8]
+    return int.from_bytes(digest, "big")
+
+
+def numpy_gen(subseed: int) -> np.random.Generator:
+    """Return a NumPy generator using the Philox bit generator."""
+    return np.random.Generator(np.random.Philox(subseed))
+
+
+def torch_gen(device: str, subseed: int) -> torch.Generator:
+    """Return a torch Generator seeded with subseed for a given device."""
+    g = torch.Generator(device)
+    g.manual_seed(subseed)
+    return g
+
+
+def set_torch_deterministic():
+    """Configure PyTorch for deterministic behavior."""
+    torch.use_deterministic_algorithms(True)
+    torch.backends.cudnn.deterministic = True
+    torch.backends.cudnn.benchmark = False
+
+
+# ------------------------- Model definition -------------------------
+
+class MLP(nn.Module):
+    def __init__(self) -> None:
+        super().__init__()
+        self.net = nn.Sequential(
+            nn.Linear(28 * 28, 300),
+            nn.ReLU(),
+            nn.Linear(300, 100),
+            nn.ReLU(),
+            nn.Linear(100, 10),
+        )
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        return self.net(x.view(x.size(0), -1))
+
+
+# ------------------------- Training utilities -------------------------
+
+@dataclass
+class RunConfig:
+    master_seed: int
+    run_id: str
+    epochs: int
+    batch_size: int
+
+
+def seed_python_np_torch(seed: int):
+    random.seed(seed)
+    # NumPy's legacy seeding expects 32-bit integers.
+    np.random.seed(seed % (2**32))
+    torch.manual_seed(seed)
+
+
+def train(cfg: RunConfig):
+    device = "cpu"
+    set_torch_deterministic()
+
+    transform = transforms.ToTensor()
+    dataset = datasets.MNIST("data", train=True, download=True, transform=transform)
+
+    # Seed before model/optimizer initialization for reproducible parameters
+    init_seed = make_subseed(cfg.master_seed, "trainer", cfg.run_id, stream_id="init")
+    seed_python_np_torch(init_seed)
+    model = MLP().to(device)
+    optimizer = torch.optim.Adam(model.parameters(), lr=1e-3)
+    criterion = nn.CrossEntropyLoss()
+
+    first_labels = None
+    first_weights_before = None
+    first_weights_after = None
+
+    for epoch in range(cfg.epochs):
+        # Seed main process for this epoch
+        trainer_seed = make_subseed(cfg.master_seed, "trainer", cfg.run_id, stream_id=epoch)
+        seed_python_np_torch(trainer_seed)
+
+        # Generator for shuffling
+        dl_gen_seed = make_subseed(cfg.master_seed, "dataloader_gen", cfg.run_id, stream_id=epoch)
+        dl_gen = torch_gen(device, dl_gen_seed)
+
+        def worker_init_fn(worker_id: int):
+            # Incorporating epoch and worker_id into the stream_id ensures each worker
+            # and each epoch has a distinct, reproducible seed stream.
+            w_seed = make_subseed(cfg.master_seed, "dataloader", cfg.run_id, stream_id=f"{epoch}|{worker_id}")
+            seed_python_np_torch(w_seed)
+
+        loader = DataLoader(
+            dataset,
+            batch_size=cfg.batch_size,
+            shuffle=True,
+            num_workers=4,
+            worker_init_fn=worker_init_fn,
+            generator=dl_gen,
+        )
+
+        for batch_idx, (data, target) in enumerate(loader):
+            data, target = data.to(device), target.to(device)
+
+            if epoch == 0 and batch_idx == 0:
+                first_labels = target[:3].tolist()
+                # Use non-border pixels so gradients are non-zero.
+                first_weights_before = (
+                    model.net[0].weight[0, 100:103].detach().clone().tolist()
+                )
+
+            optimizer.zero_grad()
+            output = model(data)
+            loss = criterion(output, target)
+            loss.backward()
+            optimizer.step()
+
+            if epoch == 0 and batch_idx == 0:
+                first_weights_after = (
+                    model.net[0].weight[0, 100:103].detach().clone().tolist()
+                )
+            break  # Only first batch needed for determinism check
+
+    return first_labels, first_weights_before, first_weights_after
+
+
+def main():
+    parser = argparse.ArgumentParser(description="Deterministic MNIST training demo")
+    parser.add_argument("--master-seed", type=int, default=2025)
+    parser.add_argument("--run-id", type=str, default="demoA")
+    parser.add_argument("--epochs", type=int, default=2)
+    parser.add_argument("--batch-size", type=int, default=64)
+    args = parser.parse_args()
+
+    cfg = RunConfig(args.master_seed, args.run_id, args.epochs, args.batch_size)
+
+    for run in range(2):
+        labels, w_before, w_after = train(cfg)
+        print(f"Run {run + 1}: labels {labels}")
+        print(f"Run {run + 1}: first-layer weights before step {w_before}")
+        print(f"Run {run + 1}: first-layer weights after step  {w_after}\n")
+
+
+if __name__ == "__main__":
+    main()