diff --git a/tests/conftest.py b/tests/conftest.py
index 3cd93f4ad3289..e8e95357ff5b9 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -987,17 +987,7 @@ class VllmRunner:
         return [req_output.outputs.score for req_output in req_outputs]
 
     def apply_model(self, func: Callable[[nn.Module], _R]) -> list[_R]:
-        if hasattr(self.llm.llm_engine, "model_executor"):
-            # This works either in V0 or in V1 with
-            # VLLM_ENABLE_V1_MULTIPROCESSING=0
-            executor = self.llm.llm_engine.model_executor
-            return executor.apply_model(func)
-
-        # This works in V1 with VLLM_ALLOW_INSECURE_SERIALIZATION=1
-        def _apply_model(self):
-            return func(self.get_model())
-
-        return self.llm.llm_engine.collective_rpc(_apply_model)
+        return self.llm.apply_model(func)
 
     def get_llm(self) -> LLM:
         return self.llm
diff --git a/tests/kernels/moe/test_mxfp4_moe.py b/tests/kernels/moe/test_mxfp4_moe.py
index a3b8f07638d9a..61d3311cc1624 100644
--- a/tests/kernels/moe/test_mxfp4_moe.py
+++ b/tests/kernels/moe/test_mxfp4_moe.py
@@ -1,21 +1,24 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
-import importlib
 import importlib.metadata
 from dataclasses import dataclass
+from importlib.util import find_spec
 from typing import Optional
 
 import pytest
 import torch
 from packaging import version
 
+from vllm.model_executor.layers.quantization.quark.quark import (  # noqa: E501
+    QuarkLinearMethod, QuarkW4A4MXFP4)
+from vllm.model_executor.layers.quantization.quark.quark_moe import (  # noqa: E501
+    QuarkW4A4MXFp4MoEMethod)
 from vllm.platforms import current_platform
 from vllm.utils.flashinfer import has_flashinfer
 
-QUARK_MXFP4_AVAILABLE = importlib.util.find_spec(
-    "quark") is not None and version.parse(
-        importlib.metadata.version("amd-quark")) >= version.parse('0.8.99')
+QUARK_MXFP4_AVAILABLE = find_spec("quark") is not None and version.parse(
+    importlib.metadata.version("amd-quark")) >= version.parse('0.8.99')
 
 TRTLLM_GEN_MXFP4_AVAILABLE = current_platform.is_cuda(
 ) and current_platform.is_device_capability(100)
@@ -39,6 +42,12 @@ class ModelCase:
     tp: int
 
 
+@pytest.fixture(scope="function", autouse=True)
+def enable_pickle(monkeypatch):
+    """`LLM.apply_model` requires pickling a function."""
+    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
+
+
 @pytest.mark.parametrize('model_case', [
     ModelCase("fxmarty/qwen_1.5-moe-a2.7b-mxfp4", tp=1),
     ModelCase("fxmarty/deepseek_r1_3_layers_mxfp4", tp=8),
@@ -55,21 +64,19 @@ def test_mxfp4_loading_and_execution_moe(vllm_runner, model_case: ModelCase):
                      tensor_parallel_size=model_case.tp,
                      load_format="dummy") as llm:
 
-        # TODO: llm.apply_model(check_model) currently relies on V0 internals.
-        # Re-enable this later.
-        # def check_model(model):
-        #     layer = model.model.layers[0]
+        def check_model(model):
+            layer = model.model.layers[0]
 
-        #     qkv_proj = layer.self_attn.qkv_proj
+            qkv_proj = layer.self_attn.qkv_proj
 
-        #     assert isinstance(qkv_proj.quant_method, QuarkLinearMethod)
-        #     assert isinstance(qkv_proj.scheme, QuarkW4A4MXFP4)
+            assert isinstance(qkv_proj.quant_method, QuarkLinearMethod)
+            assert isinstance(qkv_proj.scheme, QuarkW4A4MXFP4)
 
-        #     assert isinstance(layer.mlp.experts.quant_method,
-        #                       QuarkW4A4MXFp4MoEMethod)
+            assert isinstance(layer.mlp.experts.quant_method,
+                              QuarkW4A4MXFp4MoEMethod)
 
-        # if model_case.model_id == "fxmarty/qwen_1.5-moe-a2.7b-mxfp4":
-        #     llm.apply_model(check_model)
+        if model_case.model_id == "fxmarty/qwen_1.5-moe-a2.7b-mxfp4":
+            llm.apply_model(check_model)
 
         output = llm.generate_greedy("Today I am in the French Alps and",
                                      max_tokens=20)
diff --git a/tests/models/multimodal/generation/test_qwen2_vl.py b/tests/models/multimodal/generation/test_qwen2_vl.py
index a81f5e7ec8872..e56f4e4075be4 100644
--- a/tests/models/multimodal/generation/test_qwen2_vl.py
+++ b/tests/models/multimodal/generation/test_qwen2_vl.py
@@ -10,6 +10,7 @@ from PIL import Image
 
 from vllm.multimodal.image import rescale_image_size
 from vllm.multimodal.video import rescale_video_size, sample_frames_from_video
+from vllm.utils import set_default_torch_num_threads
 
 from ....conftest import (IMAGE_ASSETS, VIDEO_ASSETS, PromptImageInput,
                           PromptVideoInput, VllmRunner)
@@ -17,11 +18,9 @@ from ...utils import check_logprobs_close
 
 
 @pytest.fixture(scope="function", autouse=True)
-def use_v0_only(monkeypatch):
-    """
-    V1 Test: batch_make_xxxxx_embeddings calls a V0 internal
-    """
-    monkeypatch.setenv('VLLM_USE_V1', '0')
+def enable_pickle(monkeypatch):
+    """`LLM.apply_model` requires pickling a function."""
+    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
 
 
 models = ["Qwen/Qwen2-VL-2B-Instruct"]
@@ -126,9 +125,8 @@ def batch_make_image_embeddings(
             image_grid_thw_on_device = image_grid_thw.to(visual.device,
                                                          dtype=torch.int64)
             return visual(pixel_values_on_device,
-                          grid_thw=image_grid_thw_on_device)
+                          grid_thw=image_grid_thw_on_device).cpu()
 
-    # V1 Test: this calls a V0 internal.
     image_embeds = torch.concat(llm.apply_model(get_image_embeds))
 
     # split into original batches
@@ -210,7 +208,7 @@ def batch_make_video_embeddings(
             video_grid_thw_on_device = video_grid_thw.to(visual.device,
                                                          dtype=torch.int64)
             return visual(pixel_values_on_device,
-                          grid_thw=video_grid_thw_on_device)
+                          grid_thw=video_grid_thw_on_device).cpu()
 
     # V1 Test: this calls a V0 internal.
     video_embeds = torch.concat(llm.apply_model(get_image_embeds))
@@ -266,19 +264,22 @@ def run_embedding_input_test(
     processor = AutoProcessor.from_pretrained(model)
 
     # max_model_len should be greater than image_feature_size
-    with vllm_runner(model,
-                     runner="generate",
-                     max_model_len=4000,
-                     max_num_seqs=3,
-                     dtype=dtype,
-                     limit_mm_per_prompt={
-                         "image": mm_limit,
-                         "video": mm_limit
-                     },
-                     tensor_parallel_size=tensor_parallel_size,
-                     distributed_executor_backend=distributed_executor_backend
-                     ) as vllm_model:
+    with set_default_torch_num_threads(1):
+        vllm_model = vllm_runner(
+            model,
+            runner="generate",
+            max_model_len=4000,
+            max_num_seqs=3,
+            dtype=dtype,
+            limit_mm_per_prompt={
+                "image": mm_limit,
+                "video": mm_limit
+            },
+            tensor_parallel_size=tensor_parallel_size,
+            distributed_executor_backend=distributed_executor_backend,
+        )
 
+    with vllm_model:
         outputs_per_case_for_original_input = [
             vllm_model.generate_greedy_logprobs(prompts,
                                                 max_tokens,
@@ -329,9 +330,8 @@ def run_embedding_input_test(
 @pytest.mark.parametrize("max_tokens", [128])
 @pytest.mark.parametrize("num_logprobs", [10])
 def test_qwen2_vl_image_embeddings_input(vllm_runner, image_assets, model,
-                                         size_factors, dtype: str,
-                                         max_tokens: int,
-                                         num_logprobs: int) -> None:
+                                         size_factors, dtype, max_tokens,
+                                         num_logprobs, monkeypatch) -> None:
     images = [asset.pil_image for asset in image_assets]
 
     inputs_per_case: list[tuple[
diff --git a/tests/models/quantization/test_awq.py b/tests/models/quantization/test_awq.py
index bd696198931ff..7005e435ecf46 100644
--- a/tests/models/quantization/test_awq.py
+++ b/tests/models/quantization/test_awq.py
@@ -112,7 +112,7 @@ def test_awq_models(vllm_runner, image_assets, source_model, quant_model,
                     monkeypatch) -> None:
 
     # Test V1: this test hangs during setup on single-scale input.
-    # TODO: fixure out why and re-enable this on V1.
+    # TODO: figure out why and re-enable this on V1.
     monkeypatch.setenv("VLLM_USE_V1", "0")
     run_awq_test(
         vllm_runner,
diff --git a/tests/quantization/test_compressed_tensors.py b/tests/quantization/test_compressed_tensors.py
index 484f53246f349..b7949a488ad05 100644
--- a/tests/quantization/test_compressed_tensors.py
+++ b/tests/quantization/test_compressed_tensors.py
@@ -43,12 +43,9 @@ ROCM_TRITON_SCALED_MM_SUPPORTED_INT8_MODEL = [
 
 
 @pytest.fixture(scope="function", autouse=True)
-def use_v0_only(monkeypatch):
-    """
-    This module relies on V0 internals, so set VLLM_USE_V1=0.
-    """
-    if not current_platform.is_cpu():
-        monkeypatch.setenv('VLLM_USE_V1', '0')
+def enable_pickle(monkeypatch):
+    """`LLM.apply_model` requires pickling a function."""
+    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
 
 
 @pytest.mark.parametrize(
@@ -176,10 +173,11 @@ def test_compressed_tensors_w8a8_logprobs(
 
     dtype = "bfloat16"
 
-    # skip language translation prompt for the static per tensor asym model
-    if (model_path ==
-            "nm-testing/Meta-Llama-3-8B-Instruct-W8A8-Static-Per-Tensor-Asym"
-        ):  # noqa: E501
+    # skip language translation prompt for the static per tensor models
+    if model_path in (
+            "nm-testing/Meta-Llama-3-8B-Instruct-W8A8-Static-Per-Tensor-Sym",
+            "nm-testing/Meta-Llama-3-8B-Instruct-W8A8-Static-Per-Tensor-Asym",
+    ):
         example_prompts = example_prompts[0:-1]
 
     with hf_runner(model_path, dtype=dtype) as hf_model:
diff --git a/tests/quantization/test_fp8.py b/tests/quantization/test_fp8.py
index d781f462b4ad7..db53061cf2d1a 100644
--- a/tests/quantization/test_fp8.py
+++ b/tests/quantization/test_fp8.py
@@ -60,8 +60,8 @@ def test_kv_cache_model_load_and_run(vllm_runner, model_id: str,
     if use_rocm_aiter:
         monkeypatch.setenv("VLLM_ROCM_USE_AITER", "1")
 
-    # vllm_runner.apply_model() relies on V0 internals.
-    monkeypatch.setenv("VLLM_USE_V1", "0")
+    # `LLM.apply_model` requires pickling a function.
+    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
     with vllm_runner(model_id, kv_cache_dtype="fp8") as llm:
 
         def check_model(model):
@@ -104,8 +104,8 @@ def test_load_fp16_model(vllm_runner, kv_cache_dtype: str, force_marlin: bool,
     if use_rocm_aiter:
         monkeypatch.setenv("VLLM_ROCM_USE_AITER", "1")
 
-    # vllm_runner.apply_model() relies on V0 internals.
-    monkeypatch.setenv("VLLM_USE_V1", "0")
+    # `LLM.apply_model` requires pickling a function.
+    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
 
     if force_marlin:
         monkeypatch.setenv("VLLM_TEST_FORCE_FP8_MARLIN", "1")
diff --git a/tests/quantization/test_gptq_dynamic.py b/tests/quantization/test_gptq_dynamic.py
index aea50e99c1dd5..00a5946ed0154 100644
--- a/tests/quantization/test_gptq_dynamic.py
+++ b/tests/quantization/test_gptq_dynamic.py
@@ -31,41 +31,46 @@ MODEL_QUANT = [
 @pytest.mark.parametrize("model_id, use_marlin_kernel", MODEL_QUANT)
 def test_gptq_with_dynamic(vllm_runner, model_id: str, use_marlin_kernel: bool,
                            monkeypatch):
-    # vllm_runner.apply_model() relies on V0 internals.
-    monkeypatch.setenv("VLLM_USE_V1", "0")
-
-    vllm_model = vllm_runner(model_id, dtype=torch.float16, max_model_len=2048)
+    # `LLM.apply_model` requires pickling a function.
+    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
 
     linear_method_cls = GPTQMarlinLinearMethod if use_marlin_kernel else (
         GPTQLinearMethod)
 
-    for name, submodule in (vllm_model.llm.llm_engine.model_executor.
-                            driver_worker.model_runner.model.named_modules()):
-        if name == "lm_head":
-            assert isinstance(submodule.quant_method, linear_method_cls)
-        elif name == 'model.layers.0.self_attn.qkv_proj':
-            # The first layer is quantized using bits=4, group_size=128
-            # desc_act=True
-            assert isinstance(submodule.quant_method, linear_method_cls)
-            config = submodule.quant_method.quant_config
-            assert config.weight_bits == 4
-            assert config.group_size == 128
-            assert config.desc_act
-        elif name == 'model.layers.1.self_attn.qkv_proj':
-            # The second layer is quantized using bits=8, group_size=32
-            # desc_act=False
-            assert isinstance(submodule.quant_method, linear_method_cls)
-            config = submodule.quant_method.quant_config
-            assert get_dynamic_override(config, layer_name=name,
-                                        key="bits") == 8
-            assert get_dynamic_override(config,
-                                        layer_name=name,
-                                        key="group_size") == 32
-            assert not get_dynamic_override(
-                config, layer_name=name, key="desc_act")
-        elif (name == 'model.layers.2.self_attn.qkv_proj'
-              or name == 'model.layers.2.mlp.gate_up_proj'):
-            # All other layers (layer index >= 2) are not quantized
-            assert isinstance(submodule.quant_method, UnquantizedLinearMethod)
+    with vllm_runner(model_id, dtype=torch.float16, max_model_len=2048) as llm:
 
-    del vllm_model
+        def check_model(model):
+            for name, submodule in model.named_modules():
+                if name == "lm_head":
+                    assert isinstance(submodule.quant_method,
+                                      linear_method_cls)
+                elif name == 'model.layers.0.self_attn.qkv_proj':
+                    # The first layer is quantized using bits=4, group_size=128
+                    # desc_act=True
+                    assert isinstance(submodule.quant_method,
+                                      linear_method_cls)
+                    config = submodule.quant_method.quant_config
+                    assert config.weight_bits == 4
+                    assert config.group_size == 128
+                    assert config.desc_act
+                elif name == 'model.layers.1.self_attn.qkv_proj':
+                    # The second layer is quantized using bits=8, group_size=32
+                    # desc_act=False
+                    assert isinstance(submodule.quant_method,
+                                      linear_method_cls)
+                    config = submodule.quant_method.quant_config
+                    assert get_dynamic_override(config,
+                                                layer_name=name,
+                                                key="bits") == 8
+                    assert get_dynamic_override(config,
+                                                layer_name=name,
+                                                key="group_size") == 32
+                    assert not get_dynamic_override(
+                        config, layer_name=name, key="desc_act")
+                elif (name == 'model.layers.2.self_attn.qkv_proj'
+                      or name == 'model.layers.2.mlp.gate_up_proj'):
+                    # All other layers (layer index >= 2) are not quantized
+                    assert isinstance(submodule.quant_method,
+                                      UnquantizedLinearMethod)
+
+        llm.apply_model(check_model)
diff --git a/tests/quantization/test_lm_head.py b/tests/quantization/test_lm_head.py
index b24964a9d0a9f..e69d4ad349c38 100644
--- a/tests/quantization/test_lm_head.py
+++ b/tests/quantization/test_lm_head.py
@@ -29,8 +29,8 @@ def test_lm_head(
     lm_head_quantized: bool,
     monkeypatch,
 ) -> None:
-    # vllm_runner.apply_model() relies on V0 internals.
-    monkeypatch.setenv("VLLM_USE_V1", "0")
+    # `LLM.apply_model` requires pickling a function.
+    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
     with vllm_runner(model_id, dtype=torch.float16,
                      max_model_len=2048) as vllm_model:
 
diff --git a/tests/quantization/test_modelopt.py b/tests/quantization/test_modelopt.py
index c60a03f44baec..e7174be73626a 100644
--- a/tests/quantization/test_modelopt.py
+++ b/tests/quantization/test_modelopt.py
@@ -11,16 +11,12 @@ import pytest
 import torch
 
 from tests.quantization.utils import is_quant_method_supported
-from vllm.platforms import current_platform
 
 
 @pytest.fixture(scope="function", autouse=True)
-def use_v0_only(monkeypatch):
-    """
-    This module relies on V0 internals, so set VLLM_USE_V1=0.
-    """
-    if not current_platform.is_cpu():
-        monkeypatch.setenv('VLLM_USE_V1', '0')
+def enable_pickle(monkeypatch):
+    """`LLM.apply_model` requires pickling a function."""
+    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
 
 
 @pytest.mark.skipif(not is_quant_method_supported("modelopt"),
diff --git a/tests/quantization/test_ptpc_fp8.py b/tests/quantization/test_ptpc_fp8.py
index 5f78bc30504c0..088b68510cffa 100644
--- a/tests/quantization/test_ptpc_fp8.py
+++ b/tests/quantization/test_ptpc_fp8.py
@@ -13,6 +13,16 @@ from vllm.model_executor.layers.quantization.ptpc_fp8 import (
     PTPCFp8LinearMethod)
 from vllm.platforms import current_platform
 
+UNSUPPORTED_STR = (
+    "Currently torch._scaled_mm (hipBLASLt) rowwise gemm only "
+    "support output dtype of bfloat16. torch.float16 is specified.")
+
+
+@pytest.fixture(scope="function", autouse=True)
+def enable_pickle(monkeypatch):
+    """`LLM.apply_model` requires pickling a function."""
+    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
+
 
 @pytest.mark.skipif(not is_quant_method_supported("ptpc_fp8"),
                     reason="PTPC FP8 is not supported on this GPU type.")
@@ -21,14 +31,22 @@ from vllm.platforms import current_platform
 @pytest.mark.parametrize("dtype", ["auto", "bfloat16", "float16"])
 @pytest.mark.parametrize("kv_cache_dtype", ["auto", "fp8", "fp8_e4m3"])
 def test_ptpc_fp8_rocm(vllm_runner, dtype: str, kv_cache_dtype: str) -> None:
-
     try:
-        with vllm_runner("facebook/opt-125m",
-                         dtype=dtype,
-                         quantization="ptpc_fp8",
-                         kv_cache_dtype=kv_cache_dtype) as llm:
+        llm = vllm_runner("facebook/opt-125m",
+                          dtype=dtype,
+                          quantization="ptpc_fp8",
+                          kv_cache_dtype=kv_cache_dtype)
+    except AssertionError as e:
+        if str(e) == UNSUPPORTED_STR:
+            # If the error message matches, the test passes
+            return
+        else:
+            # If the error message does not match, re-raise the exception
+            raise
 
-            model = llm.model.llm_engine.model_executor.driver_worker.model_runner.model  # noqa: E501
+    with llm:
+
+        def check_model(model):
             fc1 = model.model.decoder.layers[0].fc1
             assert isinstance(fc1.quant_method, PTPCFp8LinearMethod)
             if kv_cache_dtype == "ptpc_fp8":
@@ -40,17 +58,8 @@ def test_ptpc_fp8_rocm(vllm_runner, dtype: str, kv_cache_dtype: str) -> None:
             if current_platform.has_device_capability(94):
                 # For GPUs with hardware support, we keep weights in fp8
                 assert fc1.weight.dtype == torch.float8_e4m3fnuz
-            else:
-                pytest.skip()
 
-            output = llm.generate_greedy("Hello my name is", max_tokens=20)
-            assert output
-    except AssertionError as e:
-        if str(
-                e
-        ) == "Currently torch._scaled_mm (hipBLASLt) rowwise gemm only support output dtype of bfloat16. torch.float16 is specified.":  # noqa: E501
-            # If the error message matches, the test passes
-            pass
-        else:
-            # If the error message does not match, re-raise the exception
-            raise
+        llm.apply_model(check_model)
+
+        output = llm.generate_greedy("Hello my name is", max_tokens=20)
+        assert output
diff --git a/tests/quantization/test_quark.py b/tests/quantization/test_quark.py
index c09931971e6fb..930f4acb328fd 100644
--- a/tests/quantization/test_quark.py
+++ b/tests/quantization/test_quark.py
@@ -7,10 +7,10 @@ Run `pytest tests/quantization/test_quark.py`.
 See also `tests/kernels/moe/test_mxfp4_moe.py`.
 """
 
-import importlib
 import importlib.metadata
 import os
 from dataclasses import dataclass
+from importlib.util import find_spec
 
 import huggingface_hub
 import lm_eval
@@ -24,9 +24,8 @@ from vllm.platforms import current_platform
 
 from .reference_mxfp4 import dq_mxfp4_torch, qdq_mxfp4_torch
 
-QUARK_MXFP4_AVAILABLE = importlib.util.find_spec(
-    "quark") is not None and version.parse(
-        importlib.metadata.version("amd-quark")) >= version.parse('0.8.99')
+QUARK_MXFP4_AVAILABLE = find_spec("quark") is not None and version.parse(
+    importlib.metadata.version("amd-quark")) >= version.parse('0.8.99')
 
 if QUARK_MXFP4_AVAILABLE:
     from quark.torch.export.nn.modules.realquantizer import (
@@ -43,11 +42,9 @@ except huggingface_hub.errors.RepositoryNotFoundError:
 
 
 @pytest.fixture(scope="function", autouse=True)
-def use_v0_only(monkeypatch):
-    """
-    This module relies on V0 internals, so set VLLM_USE_V1=0.
-    """
-    monkeypatch.setenv('VLLM_USE_V1', '0')
+def enable_pickle(monkeypatch):
+    """`LLM.apply_model` requires pickling a function."""
+    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
 
 
 @pytest.mark.parametrize('kv_cache_dtype', ['auto', 'fp8'])
@@ -132,13 +129,12 @@ def test_quark_fp8_parity(vllm_runner):
     }
     with (vllm_runner(quark_model_id, **llm_kwargs) as
           quark_handle, vllm_runner(fp8_model_id, **llm_kwargs) as fp8_handle):
-        quark_model = (quark_handle.llm.llm_engine.model_executor.
-                       driver_worker.model_runner.model)
-        quark_state_dict = quark_model.state_dict()
 
-        fp8_model = (fp8_handle.llm.llm_engine.model_executor.driver_worker.
-                     model_runner.model)
-        fp8_state_dict = fp8_model.state_dict()
+        def get_state_dict(model):
+            return {k: v.cpu() for k, v in model.state_dict().items()}
+
+        quark_state_dict, = quark_handle.apply_model(get_state_dict)
+        fp8_state_dict, = fp8_handle.apply_model(get_state_dict)
 
     assert fp8_state_dict.keys() == quark_state_dict.keys()
 
diff --git a/tests/quantization/test_register_quantization_config.py b/tests/quantization/test_register_quantization_config.py
index 84705e92c85bb..03fe59d7e3bff 100644
--- a/tests/quantization/test_register_quantization_config.py
+++ b/tests/quantization/test_register_quantization_config.py
@@ -105,18 +105,21 @@ def test_register_quantization_config():
                          ])
 def test_custom_quant(vllm_runner, model, monkeypatch):
     """Test infer with the custom quantization method."""
-    # vllm_runner.apply_model() relies on V0 internals.
-    monkeypatch.setenv("VLLM_USE_V1", "0")
+    # `LLM.apply_model` requires pickling a function.
+    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
+
     with vllm_runner(model_name=model,
                      quantization="custom_quant",
                      enforce_eager=True) as llm:
 
-        model = llm.llm.llm_engine.model_executor.driver_worker.model_runner.model  # noqa: E501
-        layer = model.model.layers[0]
-        qkv_proj = layer.self_attn.qkv_proj
+        def check_model(model):
+            layer = model.model.layers[0]
+            qkv_proj = layer.self_attn.qkv_proj
 
-        # Check the quantization method is FakeQuantLinearMethod
-        assert isinstance(qkv_proj.quant_method, FakeQuantLinearMethod)
+            # Check the quantization method is FakeQuantLinearMethod
+            assert isinstance(qkv_proj.quant_method, FakeQuantLinearMethod)
+
+        llm.apply_model(check_model)
 
         output = llm.generate_greedy("Hello my name is", max_tokens=20)
         assert output
diff --git a/vllm/engine/llm_engine.py b/vllm/engine/llm_engine.py
index 708f3bbeeff15..014bc56bc8ece 100644
--- a/vllm/engine/llm_engine.py
+++ b/vllm/engine/llm_engine.py
@@ -13,6 +13,7 @@ from typing import Sequence as GenericSequence
 from typing import Set, Type, Union, cast
 
 import torch
+import torch.nn as nn
 from typing_extensions import TypeVar
 
 import vllm.envs as envs
@@ -55,6 +56,7 @@ from vllm.usage.usage_lib import (UsageContext, is_usage_stats_enabled,
 from vllm.utils import Counter, Device, resolve_obj_by_qualname, weak_bind
 from vllm.version import __version__ as VLLM_VERSION
 from vllm.worker.model_runner_base import InputProcessingError
+from vllm.worker.worker_base import WorkerBase
 
 logger = init_logger(__name__)
 _LOCAL_LOGGING_INTERVAL_SEC = 5
@@ -1817,13 +1819,16 @@ class LLMEngine:
         return sampling_params
 
     def collective_rpc(self,
-                       method: Union[str, Callable[..., _R]],
+                       method: Union[str, Callable[[WorkerBase], _R]],
                        timeout: Optional[float] = None,
                        args: tuple = (),
                        kwargs: Optional[dict[str, Any]] = None) -> list[_R]:
         return self.model_executor.collective_rpc(method, timeout, args,
                                                   kwargs)
 
+    def apply_model(self, func: Callable[[nn.Module], _R]) -> list[_R]:
+        return self.collective_rpc("apply_model", args=(func, ))
+
 
 if envs.is_set("VLLM_USE_V1") and envs.VLLM_USE_V1:
     from vllm.v1.engine.llm_engine import LLMEngine as V1LLMEngine
diff --git a/vllm/entrypoints/llm.py b/vllm/entrypoints/llm.py
index e21bfce0ab085..f2282c40f7073 100644
--- a/vllm/entrypoints/llm.py
+++ b/vllm/entrypoints/llm.py
@@ -522,9 +522,14 @@ class LLM:
         """
         Run a function directly on the model inside each worker,
         returning the result for each of them.
+
+        !!! warning
+            To reduce the overhead of data transfer, avoid returning large
+            arrays or tensors from this method. If you must return them,
+            make sure you move them to CPU first to avoid taking up additional
+            VRAM!
         """
-        executor = self.llm_engine.model_executor
-        return executor.apply_model(func)
+        return self.llm_engine.apply_model(func)
 
     def _get_beam_search_lora_requests(
         self,
diff --git a/vllm/executor/executor_base.py b/vllm/executor/executor_base.py
index 42aa8d14a21eb..b75b94ad0acc2 100644
--- a/vllm/executor/executor_base.py
+++ b/vllm/executor/executor_base.py
@@ -5,11 +5,10 @@ import asyncio
 import time
 from abc import ABC, abstractmethod
 from functools import cached_property
-from typing import (Any, Awaitable, Callable, Dict, List, Optional, Set, Tuple,
-                    Union)
+from typing import Any, Awaitable, Callable, List, Optional, Set, Union
 
 import torch.nn as nn
-from typing_extensions import TypeVar
+from typing_extensions import TypeVar, deprecated
 
 import vllm.platforms
 from vllm.config import VllmConfig
@@ -63,10 +62,10 @@ class ExecutorBase(ABC):
 
     @abstractmethod
     def collective_rpc(self,
-                       method: Union[str, Callable[..., _R]],
+                       method: Union[str, Callable[[WorkerBase], _R]],
                        timeout: Optional[float] = None,
-                       args: Tuple = (),
-                       kwargs: Optional[Dict[str, Any]] = None) -> List[_R]:
+                       args: tuple = (),
+                       kwargs: Optional[dict[str, Any]] = None) -> list[_R]:
         """
         Execute an RPC call on all workers.
 
@@ -91,7 +90,7 @@ class ExecutorBase(ABC):
         """
         raise NotImplementedError
 
-    def determine_num_available_blocks(self) -> Tuple[int, int]:
+    def determine_num_available_blocks(self) -> tuple[int, int]:
         """Determine the number of available blocks for the GPU KV cache and
         swappable CPU KV cache.
 
@@ -99,9 +98,10 @@ class ExecutorBase(ABC):
         ExecutorBase may require modification of the result, e.g. to ensure the
         selected cache sizes are compatible with all workers.
 
-        Returns a Tuple[num_gpu_blocks, num_cpu_blocks], where num_gpu_blocks
-        are blocks that are "active" on the device and can be appended to.
-        num_cpu_blocks refers to "swapped" blocks in CPU memory and cannot be
+        Returns a tuple `(num_gpu_blocks, num_cpu_blocks)`, where
+        `num_gpu_blocks` are blocks that are "active" on the device and can be
+        appended to. 
+        `num_cpu_blocks` refers to "swapped" blocks in CPU memory and cannot be
         appended to.
         """
         results = self.collective_rpc("determine_num_available_blocks")
@@ -127,16 +127,15 @@ class ExecutorBase(ABC):
         self.collective_rpc("initialize_cache",
                             args=(num_gpu_blocks, num_cpu_blocks))
 
+    @deprecated("`llm_engine.model_executor.apply_model` will no longer work "
+                "in V1 Engine. Please replace with `llm_engine.apply_model` "
+                "and set `VLLM_ALLOW_INSECURE_SERIALIZATION=1`.")
     def apply_model(self, func: Callable[[nn.Module], _R]) -> list[_R]:
         """
         Run a function directly on the model inside each worker,
         returning the result for each of them.
         """
-
-        def rpc_func(worker: WorkerBase) -> _R:
-            return func(worker.get_model())
-
-        return self.collective_rpc(rpc_func)
+        return self.collective_rpc("apply_model", args=(func, ))
 
     @cached_property  # Avoid unnecessary RPC calls
     def supported_tasks(self) -> tuple[SupportedTask, ...]:
@@ -308,8 +307,8 @@ class DistributedExecutorBase(ExecutorBase):
     def collective_rpc(self,
                        method: Union[str, Callable],
                        timeout: Optional[float] = None,
-                       args: Tuple = (),
-                       kwargs: Optional[Dict] = None) -> List[Any]:
+                       args: tuple = (),
+                       kwargs: Optional[dict[str, Any]] = None) -> list[Any]:
         return self._run_workers(method, *args, **(kwargs or {}))
 
     @abstractmethod
diff --git a/vllm/v1/engine/llm_engine.py b/vllm/v1/engine/llm_engine.py
index c93bfc35f0aeb..907656d1b24cb 100644
--- a/vllm/v1/engine/llm_engine.py
+++ b/vllm/v1/engine/llm_engine.py
@@ -5,6 +5,7 @@ from collections.abc import Mapping
 from copy import copy
 from typing import Any, Callable, Optional, Union
 
+import torch.nn as nn
 from typing_extensions import TypeVar
 
 import vllm.envs as envs
@@ -33,6 +34,7 @@ from vllm.v1.metrics.loggers import (PrometheusStatLogger, StatLoggerBase,
                                      StatLoggerFactory)
 from vllm.v1.metrics.reader import Metric, get_metrics_snapshot
 from vllm.v1.metrics.stats import IterationStats
+from vllm.v1.worker.worker_base import WorkerBase
 
 logger = init_logger(__name__)
 
@@ -319,12 +321,15 @@ class LLMEngine:
         return self.engine_core.pin_lora(lora_id)
 
     def collective_rpc(self,
-                       method: Union[str, Callable[..., _R]],
+                       method: Union[str, Callable[[WorkerBase], _R]],
                        timeout: Optional[float] = None,
                        args: tuple = (),
                        kwargs: Optional[dict[str, Any]] = None) -> list[_R]:
         return self.engine_core.collective_rpc(method, timeout, args, kwargs)
 
+    def apply_model(self, func: Callable[[nn.Module], _R]) -> list[_R]:
+        return self.collective_rpc("apply_model", args=(func, ))
+
     def __del__(self):
         if dp_group := getattr(self, "dp_group", None):
             stateless_destroy_torch_distributed_process_group(dp_group)
diff --git a/vllm/worker/worker_base.py b/vllm/worker/worker_base.py
index aa76d21f0fcaa..d0a56f6ff4637 100644
--- a/vllm/worker/worker_base.py
+++ b/vllm/worker/worker_base.py
@@ -5,7 +5,8 @@ import dataclasses
 import os
 import time
 from abc import abstractmethod
-from typing import Any, Dict, List, Optional, Set, Tuple, Type, Union
+from typing import (Any, Callable, Dict, List, Optional, Set, Tuple, Type,
+                    TypeVar, Union)
 
 import cloudpickle
 import torch
@@ -28,6 +29,8 @@ from vllm.worker.model_runner_base import (BroadcastableModelInput,
 
 logger = init_logger(__name__)
 
+_R = TypeVar("_R")
+
 
 @warn_for_unimplemented_methods
 class WorkerBase:
@@ -70,6 +73,10 @@ class WorkerBase:
     def get_model(self) -> nn.Module:
         raise NotImplementedError
 
+    def apply_model(self, fn: Callable[[nn.Module], _R]) -> _R:
+        """Apply a function on the model inside this worker."""
+        return fn(self.get_model())
+
     def load_model(self) -> None:
         """Load model onto target device."""
         raise NotImplementedError