diff --git a/tests/distributed/omni_connectors/test_basic_connectors.py b/tests/distributed/omni_connectors/test_basic_connectors.py
index 787d5594b..2cd0fcea3 100644
--- a/tests/distributed/omni_connectors/test_basic_connectors.py
+++ b/tests/distributed/omni_connectors/test_basic_connectors.py
@@ -33,6 +33,18 @@ def test_tensor_serialization():
     assert torch.equal(tensor, deserialized)
 
 
+def test_bfloat16_tensor_serialization():
+    """The raw tensor serializer preserves the Mammoth BF16 wire dtype."""
+    import torch
+
+    tensor = torch.tensor([[1.0, -2.5], [3.25, 4.5]], dtype=torch.bfloat16)
+    serialized = OmniSerializer.serialize({"text_prompt_embeds": tensor})
+    deserialized = OmniSerializer.deserialize(serialized)
+
+    assert deserialized["text_prompt_embeds"].dtype == torch.bfloat16
+    assert torch.equal(deserialized["text_prompt_embeds"], tensor)
+
+
 def test_noncontiguous_tensor_serialization():
     """Test torch.Tensor serialization for strided views."""
     import torch
diff --git a/tests/model_executor/stage_input_processors/test_mammoth_moda2.py b/tests/model_executor/stage_input_processors/test_mammoth_moda2.py
new file mode 100644
index 000000000..992908c36
--- /dev/null
+++ b/tests/model_executor/stage_input_processors/test_mammoth_moda2.py
@@ -0,0 +1,185 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""CPU regression tests for MammothModa2's completed-AR to DiT bridge."""
+
+from types import SimpleNamespace
+
+import pytest
+import torch
+
+from vllm_omni.diffusion.models.mammoth_moda2.pipeline_mammothmoda2_dit import (
+    MammothModa2DiTPipeline,
+)
+from vllm_omni.engine.serialization import (
+    deserialize_additional_information,
+    serialize_additional_information,
+)
+from vllm_omni.engine.stage_engine_core_client import StageEngineCoreClient
+from vllm_omni.model_executor.models.mammoth_moda2.pipeline import MAMMOTH_MODA2_PIPELINE
+from vllm_omni.model_executor.stage_input_processors.mammoth_moda2 import ar2dit
+
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
+
+_PROMPT_TOKEN_IDS = [7, 8, 9]
+_GENERATED_TOKEN_IDS = [101, 102, 103]
+
+
+def _hidden_states(rows: int = 5, dtype: torch.dtype = torch.bfloat16) -> torch.Tensor:
+    return torch.arange(rows * 4, dtype=dtype).reshape(rows, 4)
+
+
+def _ar_output(hidden_states: torch.Tensor | None = None) -> SimpleNamespace:
+    multimodal_output = {} if hidden_states is None else {"latent": hidden_states}
+    return SimpleNamespace(
+        request_id="mammoth-request",
+        prompt_token_ids=list(_PROMPT_TOKEN_IDS),
+        outputs=[
+            SimpleNamespace(
+                cumulative_token_ids=list(_GENERATED_TOKEN_IDS),
+                multimodal_output=multimodal_output,
+            )
+        ],
+    )
+
+
+def _prompt(
+    *,
+    target_h: int | None = None,
+    target_w: int | None = None,
+) -> dict[str, object]:
+    mm_processor_kwargs: dict[str, int] = {}
+    if target_h is not None:
+        mm_processor_kwargs["target_h"] = target_h
+    if target_w is not None:
+        mm_processor_kwargs["target_w"] = target_w
+    return {
+        "additional_information": {
+            "image_height": [384],
+            "image_width": [640],
+            "text_guidance_scale": [4.5],
+            "cfg_range": [0.1, 0.9],
+            "num_inference_steps": [20],
+        },
+        "mm_processor_kwargs": mm_processor_kwargs,
+    }
+
+
+def _assert_complete_dit_input(dit_inputs: list[dict[str, object]], hidden_states: torch.Tensor) -> None:
+    assert len(dit_inputs) == 1
+    dit_input = dit_inputs[0]
+    assert dit_input["prompt_token_ids"] == [0]
+
+    additional_information = dit_input["additional_information"]
+    assert isinstance(additional_information, dict)
+    full_hidden_states = additional_information["full_hidden_states"]
+    assert isinstance(full_hidden_states, torch.Tensor)
+    assert full_hidden_states.dtype == torch.bfloat16
+    assert full_hidden_states.is_contiguous()
+    assert torch.equal(full_hidden_states, hidden_states)
+    assert additional_information["full_token_ids"] == [7, 8, 9, 101, 102]
+    assert additional_information["answer_start_index"] == [3]
+    assert additional_information["image_height"] == [384]
+    assert additional_information["image_width"] == [640]
+    assert additional_information["text_guidance_scale"] == [4.5]
+    assert additional_information["cfg_range"] == [0.1, 0.9]
+    assert additional_information["num_inference_steps"] == [20]
+
+
+def test_ar2dit_builds_one_complete_dit_input() -> None:
+    hidden_states = _hidden_states()
+
+    dit_inputs = ar2dit([_ar_output(hidden_states)], _prompt())
+
+    _assert_complete_dit_input(dit_inputs, hidden_states)
+
+
+@pytest.mark.parametrize("dtype", (torch.float16, torch.bfloat16))
+def test_ar2dit_preserves_low_precision_through_engine_core_payload(dtype: torch.dtype) -> None:
+    hidden_states = _hidden_states(dtype=dtype)
+    dit_input = ar2dit([_ar_output(hidden_states)], _prompt())[0]
+
+    wire_payload = serialize_additional_information(dit_input["additional_information"])
+    assert wire_payload is not None
+    restored = deserialize_additional_information(wire_payload)
+    restored_hidden_states = restored["full_hidden_states"]
+
+    assert isinstance(restored_hidden_states, torch.Tensor)
+    assert restored_hidden_states.dtype == dtype
+    assert restored_hidden_states.is_contiguous()
+    assert torch.equal(restored_hidden_states, hidden_states)
+
+
+@pytest.mark.parametrize("dtype", (torch.float16, torch.bfloat16))
+def test_dit_condition_split_preserves_compact_transfer_dtype(dtype: torch.dtype) -> None:
+    # Construct only the config read by _split_ar_conditions.  This keeps the
+    # test CPU-only and avoids loading the DiT/VAE weights.
+    pipeline = object.__new__(MammothModa2DiTPipeline)
+    object.__setattr__(
+        pipeline,
+        "config",
+        SimpleNamespace(
+            llm_config=SimpleNamespace(gen_vocab_start_index=100),
+            image_token_id=20,
+            video_token_id=21,
+            vision_start_token_id=22,
+            vision_end_token_id=23,
+        ),
+    )
+    hidden_states = _hidden_states(dtype=dtype)
+
+    text_cond, image_cond = pipeline._split_ar_conditions(
+        full_hidden_states=hidden_states,
+        full_token_ids=[7, 20, 8, 101, 102],
+        answer_start_index=3,
+    )
+
+    assert text_cond.dtype == dtype
+    assert image_cond.dtype == dtype
+    assert text_cond.is_contiguous()
+    assert image_cond.is_contiguous()
+    assert torch.equal(text_cond, hidden_states[[0, 2]])
+    assert torch.equal(image_cond, hidden_states[[3, 4]])
+
+
+def test_ar2dit_prefers_processor_image_dimensions() -> None:
+    hidden_states = _hidden_states()
+
+    dit_inputs = ar2dit([_ar_output(hidden_states)], _prompt(target_h=512, target_w=768))
+
+    additional_information = dit_inputs[0]["additional_information"]
+    assert additional_information["image_height"] == [512]
+    assert additional_information["image_width"] == [768]
+
+
+def test_ar2dit_rejects_missing_latent_output() -> None:
+    with pytest.raises(ValueError, match="missing latent multimodal output"):
+        ar2dit([_ar_output()], _prompt())
+
+
+def test_ar2dit_rejects_hidden_token_row_mismatch() -> None:
+    with pytest.raises(AssertionError, match="Hidden states length mismatch"):
+        ar2dit([_ar_output(_hidden_states(rows=4))], _prompt())
+
+
+def test_mammoth_pipeline_uses_standard_completed_ar_forwarding() -> None:
+    stage0, stage1 = MAMMOTH_MODA2_PIPELINE.stages
+
+    assert stage0.custom_process_next_stage_input_func is None
+    assert stage1.custom_process_input_func.endswith(".ar2dit")
+    assert stage1.sync_process_input_func is None
+    assert stage1.requires_full_payload_input is False
+
+
+def test_stage_client_forwards_completed_ar_output_to_mammoth_adapter() -> None:
+    hidden_states = _hidden_states()
+    client = object.__new__(StageEngineCoreClient)
+    client.custom_process_input_func = ar2dit
+    client.requires_multimodal_data = False
+
+    dit_inputs = client.process_engine_inputs(
+        [_ar_output(hidden_states)],
+        _prompt(),
+    )
+
+    _assert_complete_dit_input(dit_inputs, hidden_states)
diff --git a/vllm_omni/diffusion/models/mammoth_moda2/pipeline_mammothmoda2_dit.py b/vllm_omni/diffusion/models/mammoth_moda2/pipeline_mammothmoda2_dit.py
index 5298d5514..c96e5548c 100644
--- a/vllm_omni/diffusion/models/mammoth_moda2/pipeline_mammothmoda2_dit.py
+++ b/vllm_omni/diffusion/models/mammoth_moda2/pipeline_mammothmoda2_dit.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
 from __future__ import annotations
 
 from collections.abc import Iterable
@@ -191,8 +193,12 @@ class MammothModa2DiTPipeline(nn.Module, SupportsComponentDiscovery):
         text_mask = questions_mask & ~(visual_token_mask | gen_token_mask)
         image_mask = answers_mask & gen_token_mask
 
-        text_cond = full_hidden_states[text_mask].to(dtype=torch.float32).contiguous()
-        image_cond = full_hidden_states[image_mask].to(dtype=torch.float32).contiguous()
+        # Keep the transferred representation compact until the final device/dtype
+        # conversion in ``forward``.  The masks are dtype-independent, and an
+        # unconditional host-side float32 expansion here would otherwise double both
+        # the selected-condition staging footprint and BF16 H2D traffic.
+        text_cond = full_hidden_states[text_mask].contiguous()
+        image_cond = full_hidden_states[image_mask].contiguous()
         return text_cond, image_cond
 
     @torch.inference_mode()
diff --git a/vllm_omni/model_executor/stage_input_processors/mammoth_moda2.py b/vllm_omni/model_executor/stage_input_processors/mammoth_moda2.py
index 7b23f8e49..fab22b739 100644
--- a/vllm_omni/model_executor/stage_input_processors/mammoth_moda2.py
+++ b/vllm_omni/model_executor/stage_input_processors/mammoth_moda2.py
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
 """Stage input processor for MammothModa2 (AR -> DiT)."""
 
 from collections.abc import Mapping
@@ -91,9 +93,11 @@ def ar2dit(
         # from the model config. Pass through the raw AR hidden states + token ids and
         # the question/answer boundary so the pipeline can reconstruct the masks.
         additional_information = {
-            # float32 so the tensor crosses the stage boundary (the serializer uses
-            # numpy, which has no bf16); the DiT re-casts to the model dtype.
-            "full_hidden_states": full_hidden_states.float().contiguous(),
+            # The EngineCore payload serializer preserves bfloat16 as raw bytes.
+            # Keep the AR representation compact across the CPU/IPC boundary;
+            # the DiT selects its conditioning rows and casts them only when it
+            # consumes them.
+            "full_hidden_states": full_hidden_states.contiguous(),
             "full_token_ids": full_token_ids,
             "answer_start_index": [len(prompt_token_ids)],
             "image_height": [int(image_height)],