diff --git a/modules/modelSetup/BaseChromaSetup.py b/modules/modelSetup/BaseChromaSetup.py
index 0eb623399..0b8b1a437 100644
--- a/modules/modelSetup/BaseChromaSetup.py
+++ b/modules/modelSetup/BaseChromaSetup.py
@@ -165,7 +165,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -196,6 +196,7 @@ def predict(
                 generator,
                 scaled_latent_image.shape[0],
                 config,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             scaled_noisy_latent_image, sigma = self._add_noise_discrete(
diff --git a/modules/modelSetup/BaseErnieSetup.py b/modules/modelSetup/BaseErnieSetup.py
index c164dc0bc..ec91320c2 100644
--- a/modules/modelSetup/BaseErnieSetup.py
+++ b/modules/modelSetup/BaseErnieSetup.py
@@ -79,7 +79,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -110,6 +110,7 @@ def predict(
                 scaled_latent_image.shape[0],
                 config,
                 shift=shift if config.dynamic_timestep_shifting else config.timestep_shift,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             scaled_noisy_latent_image, sigma = self._add_noise_discrete(
diff --git a/modules/modelSetup/BaseFlux2Setup.py b/modules/modelSetup/BaseFlux2Setup.py
index b91cd8af8..19b2074f1 100644
--- a/modules/modelSetup/BaseFlux2Setup.py
+++ b/modules/modelSetup/BaseFlux2Setup.py
@@ -89,7 +89,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -119,6 +119,7 @@ def predict(
                 scaled_latent_image.shape[0],
                 config,
                 shift = shift if config.dynamic_timestep_shifting else config.timestep_shift,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             scaled_noisy_latent_image, sigma = self._add_noise_discrete(
diff --git a/modules/modelSetup/BaseFluxSetup.py b/modules/modelSetup/BaseFluxSetup.py
index 9bae83cde..b13611f75 100644
--- a/modules/modelSetup/BaseFluxSetup.py
+++ b/modules/modelSetup/BaseFluxSetup.py
@@ -204,7 +204,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -249,6 +249,7 @@ def predict(
                 scaled_latent_image.shape[0],
                 config,
                 shift = shift if config.dynamic_timestep_shifting else config.timestep_shift,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             scaled_noisy_latent_image, sigma = self._add_noise_discrete(
diff --git a/modules/modelSetup/BaseHiDreamSetup.py b/modules/modelSetup/BaseHiDreamSetup.py
index 17fbcc0d6..c63516547 100644
--- a/modules/modelSetup/BaseHiDreamSetup.py
+++ b/modules/modelSetup/BaseHiDreamSetup.py
@@ -297,7 +297,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -348,6 +348,7 @@ def predict(
                 generator,
                 scaled_latent_image.shape[0],
                 config,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             scaled_noisy_latent_image, sigma = self._add_noise_discrete(
diff --git a/modules/modelSetup/BaseHunyuanVideoSetup.py b/modules/modelSetup/BaseHunyuanVideoSetup.py
index b072bf4ba..1ef4c688e 100644
--- a/modules/modelSetup/BaseHunyuanVideoSetup.py
+++ b/modules/modelSetup/BaseHunyuanVideoSetup.py
@@ -205,7 +205,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -243,6 +243,7 @@ def predict(
                 generator,
                 scaled_latent_image.shape[0],
                 config,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             scaled_noisy_latent_image, sigma = self._add_noise_discrete(
diff --git a/modules/modelSetup/BasePixArtAlphaSetup.py b/modules/modelSetup/BasePixArtAlphaSetup.py
index 3069b4884..2c818866e 100644
--- a/modules/modelSetup/BasePixArtAlphaSetup.py
+++ b/modules/modelSetup/BasePixArtAlphaSetup.py
@@ -159,7 +159,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -193,6 +193,7 @@ def predict(
                 generator,
                 scaled_latent_image.shape[0],
                 config,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             scaled_noisy_latent_image = self._add_noise_discrete(
diff --git a/modules/modelSetup/BaseQwenSetup.py b/modules/modelSetup/BaseQwenSetup.py
index a8a7be8f6..38095d775 100644
--- a/modules/modelSetup/BaseQwenSetup.py
+++ b/modules/modelSetup/BaseQwenSetup.py
@@ -86,7 +86,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -114,6 +114,7 @@ def predict(
                 scaled_latent_image.shape[0],
                 config,
                 shift = shift if config.dynamic_timestep_shifting else config.timestep_shift,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             scaled_noisy_latent_image, sigma = self._add_noise_discrete(
diff --git a/modules/modelSetup/BaseSanaSetup.py b/modules/modelSetup/BaseSanaSetup.py
index 0c9ea6da0..c32d92127 100644
--- a/modules/modelSetup/BaseSanaSetup.py
+++ b/modules/modelSetup/BaseSanaSetup.py
@@ -169,7 +169,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -203,6 +203,7 @@ def predict(
                 generator,
                 scaled_latent_image.shape[0],
                 config,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             scaled_noisy_latent_image, sigma = self._add_noise_discrete(
diff --git a/modules/modelSetup/BaseStableDiffusion3Setup.py b/modules/modelSetup/BaseStableDiffusion3Setup.py
index de5dc04e8..6b320bc6d 100644
--- a/modules/modelSetup/BaseStableDiffusion3Setup.py
+++ b/modules/modelSetup/BaseStableDiffusion3Setup.py
@@ -247,7 +247,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -300,6 +300,7 @@ def predict(
                 generator,
                 scaled_latent_image.shape[0],
                 config,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             scaled_noisy_latent_image, sigma = self._add_noise_discrete(
diff --git a/modules/modelSetup/BaseStableDiffusionSetup.py b/modules/modelSetup/BaseStableDiffusionSetup.py
index 8cf63ac07..52c374b3a 100644
--- a/modules/modelSetup/BaseStableDiffusionSetup.py
+++ b/modules/modelSetup/BaseStableDiffusionSetup.py
@@ -151,7 +151,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -182,6 +182,7 @@ def predict(
                 generator,
                 scaled_latent_image.shape[0],
                 config,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             latent_noise = self._create_noise(
diff --git a/modules/modelSetup/BaseStableDiffusionXLSetup.py b/modules/modelSetup/BaseStableDiffusionXLSetup.py
index 61cb1e457..d22d21798 100644
--- a/modules/modelSetup/BaseStableDiffusionXLSetup.py
+++ b/modules/modelSetup/BaseStableDiffusionXLSetup.py
@@ -195,7 +195,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -233,6 +233,7 @@ def predict(
                 generator,
                 scaled_latent_image.shape[0],
                 config,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             latent_noise = self._create_noise(
diff --git a/modules/modelSetup/BaseWuerstchenSetup.py b/modules/modelSetup/BaseWuerstchenSetup.py
index 48cd05942..df3c5a4ce 100644
--- a/modules/modelSetup/BaseWuerstchenSetup.py
+++ b/modules/modelSetup/BaseWuerstchenSetup.py
@@ -210,7 +210,7 @@ def predict(
             elif model.model_type.is_stable_cascade():
                 scaled_latent_image = latent_image
 
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -222,6 +222,7 @@ def predict(
                 generator,
                 scaled_latent_image.shape[0],
                 config,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             if model.model_type.is_wuerstchen_v2():
diff --git a/modules/modelSetup/BaseZImageSetup.py b/modules/modelSetup/BaseZImageSetup.py
index b822d7304..66e4e5e02 100644
--- a/modules/modelSetup/BaseZImageSetup.py
+++ b/modules/modelSetup/BaseZImageSetup.py
@@ -88,7 +88,7 @@ def predict(
             deterministic: bool = False,
     ) -> dict:
         with model.autocast_context:
-            batch_seed = 0 if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
+            batch_seed = int(batch.get("__val_noise_seed__", 0)) if deterministic else train_progress.global_step * multi.world_size() + multi.rank()
             generator = torch.Generator(device=config.train_device)
             generator.manual_seed(batch_seed)
             rand = Random(batch_seed)
@@ -114,6 +114,7 @@ def predict(
                 scaled_latent_image.shape[0],
                 config,
                 shift = shift if config.dynamic_timestep_shifting else config.timestep_shift,
+                validation_override=batch.get("__val_timestep_unit__"),
             )
 
             scaled_noisy_latent_image, sigma = self._add_noise_discrete(
diff --git a/modules/modelSetup/mixin/ModelSetupNoiseMixin.py b/modules/modelSetup/mixin/ModelSetupNoiseMixin.py
index 1285caba8..f37765b7f 100644
--- a/modules/modelSetup/mixin/ModelSetupNoiseMixin.py
+++ b/modules/modelSetup/mixin/ModelSetupNoiseMixin.py
@@ -126,14 +126,21 @@ def _get_timestep_discrete(
             batch_size: int,
             config: TrainConfig,
             shift: float = None,
+            validation_override: float | None = None,
     ) -> Tensor:
         if shift is None:
             shift = config.timestep_shift
 
         if deterministic:
-            # -1 is for zero-based indexing
+            if validation_override is not None:
+                # Already-shifted unit position in [0, 1]; map to integer timestep.
+                t = int(validation_override * num_train_timesteps)
+                t = max(0, min(num_train_timesteps - 1, t))
+            else:
+                # -1 is for zero-based indexing
+                t = int(num_train_timesteps * 0.5) - 1
             return torch.tensor(
-                int(num_train_timesteps * 0.5) - 1,
+                t,
                 dtype=torch.long,
                 device=generator.device,
             ).unsqueeze(0)
@@ -217,11 +224,13 @@ def _get_timestep_continuous(
             generator: Generator,
             batch_size: int,
             config: TrainConfig,
+            validation_override: float | None = None,
     ) -> Tensor:
         if deterministic:
+            fill_value = float(validation_override) if validation_override is not None else 0.5
             return torch.full(
                 size=(batch_size,),
-                fill_value=0.5,
+                fill_value=fill_value,
                 device=generator.device,
             )
         else:
diff --git a/modules/trainer/GenericTrainer.py b/modules/trainer/GenericTrainer.py
index ab4926901..f3d0a66e0 100644
--- a/modules/trainer/GenericTrainer.py
+++ b/modules/trainer/GenericTrainer.py
@@ -20,6 +20,7 @@
 from modules.util.bf16_stochastic_rounding import set_seed as bf16_stochastic_rounding_set_seed
 from modules.util.callbacks.TrainCallbacks import TrainCallbacks
 from modules.util.commands.TrainCommands import TrainCommands
+from modules.util.config.ConceptConfig import ConceptConfig
 from modules.util.config.SampleConfig import SampleConfig
 from modules.util.config.TrainConfig import TrainConfig
 from modules.util.dtype_util import create_grad_scaler, enable_grad_scaling
@@ -33,6 +34,11 @@
 from modules.util.time_util import get_string_timestamp
 from modules.util.torch_util import torch_gc
 from modules.util.TrainProgress import TrainProgress
+from modules.util.validation_timestep import (
+    apply_timestep_shift_unit,
+    stratified_unit_position,
+    validation_noise_seed,
+)
 
 import torch
 from torch import Tensor, nn
@@ -364,20 +370,35 @@ def __validate(self, train_progress: TrainProgress):
             mapping_seed_to_label = {}
             mapping_label_to_seed = {}
 
-            for validation_batch in step_tqdm_validation:
+            concept_shift_by_seed = self.__validation_concept_shifts()
+            global_validation_shift = self.config.validation_timestep_shift
+            n_validation = current_epoch_length_validation
+
+            for i, validation_batch in enumerate(step_tqdm_validation):
                 if self.__needs_gc(train_progress):
                     torch_gc()
 
+                # since validation batch size = 1
+                concept_name = validation_batch["concept_name"][0]
+                concept_path = validation_batch["concept_path"][0]
+                concept_seed = validation_batch["concept_seed"].item()
+
+                shift_for_sample = concept_shift_by_seed.get(concept_seed)
+                if shift_for_sample is None:
+                    shift_for_sample = global_validation_shift
+
+                pos = stratified_unit_position(i, n_validation)
+                validation_batch["__val_timestep_unit__"] = apply_timestep_shift_unit(
+                    pos, shift_for_sample
+                )
+                validation_batch["__val_noise_seed__"] = validation_noise_seed(i)
+
                 with torch.no_grad():
                     model_output_data = self.model_setup.predict(
                         self.model, validation_batch, self.config, train_progress, deterministic=True)
                     loss_validation = self.model_setup.calculate_loss(
                         self.model, validation_batch, model_output_data, self.config)
 
-                # since validation batch size = 1
-                concept_name = validation_batch["concept_name"][0]
-                concept_path = validation_batch["concept_path"][0]
-                concept_seed = validation_batch["concept_seed"].item()
                 loss = loss_validation.item()
 
                 label = concept_name if concept_name else os.path.basename(concept_path)
@@ -413,6 +434,19 @@ def __validate(self, train_progress: TrainProgress):
                                             total_average_loss,
                                             train_progress.global_step)
 
+    def __validation_concept_shifts(self) -> dict[int, float]:
+        concepts = self.config.concepts
+        if concepts is None:
+            with open(self.config.concept_file_name, 'r') as f:
+                concepts = [ConceptConfig.default_values().from_dict(c) for c in json.load(f)]
+
+        return {
+            concept.seed: concept.validation_timestep_shift
+            for concept in concepts
+            if ConceptType(concept.type) == ConceptType.VALIDATION
+            and concept.validation_timestep_shift is not None
+        }
+
     def __save_backup_config(self, backup_path):
         config_path = os.path.join(backup_path, "onetrainer_config")
         args_path = path_util.canonical_join(config_path, "args.json")
diff --git a/modules/ui/ConceptWindow.py b/modules/ui/ConceptWindow.py
index f58879d5f..99ba58dbc 100644
--- a/modules/ui/ConceptWindow.py
+++ b/modules/ui/ConceptWindow.py
@@ -198,6 +198,12 @@ def set_prompt_path_entry_enabled(option: str):
                          tooltip="The loss multiplyer for this concept.")
         components.entry(frame, 9, 1, self.ui_state, "loss_weight")
 
+        # validation timestep shift (only meaningful for VALIDATION concepts)
+        components.label(frame, 10, 0, "Validation Timestep Shift",
+                         tooltip="Per-concept override for the global Validation Timestep Shift. Leave blank to inherit. Only used for VALIDATION concepts.",
+                         wide_tooltip=True)
+        components.entry(frame, 10, 1, self.ui_state, "validation_timestep_shift")
+
         frame.pack(fill="both", expand=1)
         return frame
 
diff --git a/modules/ui/TrainingTab.py b/modules/ui/TrainingTab.py
index bcca11ae9..f21570279 100644
--- a/modules/ui/TrainingTab.py
+++ b/modules/ui/TrainingTab.py
@@ -691,11 +691,16 @@ def __create_noise_frame(self, master, row, supports_generalized_offset_noise: b
                          tooltip="Shift the timestep distribution. Use the preview to see more details.")
         components.entry(frame, 8, 1, self.ui_state, "timestep_shift", required=True)
 
+        # validation timestep shift
+        components.label(frame, 9, 0, "Validation Timestep Shift",
+                         tooltip="Shift the validation timestep distribution. Concepts can override this value individually.")
+        components.entry(frame, 9, 1, self.ui_state, "validation_timestep_shift", required=True)
+
         if supports_dynamic_timestep_shifting:
             # dynamic timestep shifting
-            components.label(frame, 9, 0, "Dynamic Timestep Shifting",
+            components.label(frame, 10, 0, "Dynamic Timestep Shifting",
                              tooltip="Dynamically shift the timestep distribution based on resolution. If enabled, the shifting parameters are taken from the model's scheduler configuration and Timestep Shift is ignored. Note: For Z-Image and Flux2, the dynamic shifting parameters are likely wrong and unknown. Use with care or set your own, fixed shift.", wide_tooltip=True)
-            components.switch(frame, 9, 1, self.ui_state, "dynamic_timestep_shifting")
+            components.switch(frame, 10, 1, self.ui_state, "dynamic_timestep_shifting")
 
 
 
diff --git a/modules/util/config/ConceptConfig.py b/modules/util/config/ConceptConfig.py
index d315b63ad..9ddc803e4 100644
--- a/modules/util/config/ConceptConfig.py
+++ b/modules/util/config/ConceptConfig.py
@@ -136,6 +136,7 @@ class ConceptConfig(BaseConfig):
     text_variations: int
     repeats: float
     loss_weight: float
+    validation_timestep_shift: float | None
     concept_stats: dict
 
     image: ConceptImageConfig
@@ -195,6 +196,7 @@ def default_values():
         data.append(("balancing", 1.0, float, False))
         data.append(("balancing_strategy", BalancingStrategy.REPEATS, BalancingStrategy, False))
         data.append(("loss_weight", 1.0, float, False))
+        data.append(("validation_timestep_shift", None, float, True))
         data.append(("concept_stats", {}, dict, False))
 
         return ConceptConfig(data)
diff --git a/modules/util/config/TrainConfig.py b/modules/util/config/TrainConfig.py
index 1c940da66..2f921f001 100644
--- a/modules/util/config/TrainConfig.py
+++ b/modules/util/config/TrainConfig.py
@@ -447,6 +447,7 @@ class TrainConfig(BaseConfig):
 
     timestep_shift: float
     dynamic_timestep_shifting: bool
+    validation_timestep_shift: float
 
     # unet
     unet: TrainModelPartConfig
@@ -1024,6 +1025,7 @@ def default_values() -> 'TrainConfig':
         data.append(("noising_bias", 0.0, float, False))
         data.append(("timestep_shift", 1.0, float, False))
         data.append(("dynamic_timestep_shifting", False, bool, False))
+        data.append(("validation_timestep_shift", 1.0, float, False))
 
 
         # unet
diff --git a/modules/util/validation_timestep.py b/modules/util/validation_timestep.py
new file mode 100644
index 000000000..ae95784c3
--- /dev/null
+++ b/modules/util/validation_timestep.py
@@ -0,0 +1,34 @@
+"""Deterministic stratified validation timestep + noise assignment.
+
+Validation loss is averaged across the full timestep distribution by giving each
+sample a unique, persistent timestep derived from its index. Splitting [0, 1]
+into N equal bins and jittering the position within each bin gives an even
+spread at any N while remaining reproducible: identical configs and datasets
+yield identical assignments.
+"""
+
+import numpy as np
+
+# Distinct large constants keep the timestep stream and the noise stream
+# independent. Changing these values changes everyone's validation losses, so
+# they are baked in.
+VAL_SEED = 0
+TIMESTEP_TAG = 0xA5F13C7B
+NOISE_TAG = 0x5E2D88C1
+
+
+def stratified_unit_position(i: int, n: int, seed: int = VAL_SEED) -> float:
+    if n <= 0:
+        return 0.0
+    jitter = float(np.random.default_rng([seed, TIMESTEP_TAG, i]).random())
+    return (i + jitter) / n
+
+
+def validation_noise_seed(i: int, seed: int = VAL_SEED) -> int:
+    return int(np.random.default_rng([seed, NOISE_TAG, i]).integers(0, 2 ** 31))
+
+
+def apply_timestep_shift_unit(pos: float, shift: float) -> float:
+    if shift == 1.0:
+        return pos
+    return shift * pos / ((shift - 1.0) * pos + 1.0)