diff --git a/src/engine/ov_genai/llm.py b/src/engine/ov_genai/llm.py
index 84621f0..673fdd8 100755
--- a/src/engine/ov_genai/llm.py
+++ b/src/engine/ov_genai/llm.py
@@ -1,4 +1,7 @@
-from src.engine.ov_genai.utils import extract_scheduler_config_from_loader
+from src.engine.ov_genai.utils import (
+    apply_temperature,
+    extract_scheduler_config_from_loader,
+)
 import asyncio
 import gc
 import logging
@@ -322,7 +325,7 @@ def create_generation_config(self, config: OVGenAI_GenConfig) -> GenerationConfi
         """
         generation_kwargs = self.model.get_generation_config() if self.model else GenerationConfig()
         generation_kwargs.max_new_tokens = config.max_tokens
-        generation_kwargs.temperature = config.temperature
+        apply_temperature(generation_kwargs, config.temperature)
         generation_kwargs.top_k = config.top_k
         generation_kwargs.top_p = config.top_p
         generation_kwargs.repetition_penalty = config.repetition_penalty
diff --git a/src/engine/ov_genai/utils.py b/src/engine/ov_genai/utils.py
index 973f3a1..746a644 100644
--- a/src/engine/ov_genai/utils.py
+++ b/src/engine/ov_genai/utils.py
@@ -2,13 +2,26 @@
 import logging
 from typing import Literal
 
-from openvino_genai import SchedulerConfig
+from openvino_genai import GenerationConfig, SchedulerConfig
 
 from src.server.schemas.modeling.contract_ovgenai_llm_and_vlm import SchedulerConfigSchema
 from src.server.schemas.registration import ModelLoadConfig
 
 logger = logging.getLogger(__name__)
 
+
+def apply_temperature(generation_config: GenerationConfig, temperature: float) -> None:
+    """Set the sampling temperature, falling back to greedy decoding at zero.
+
+    OpenAI treats temperature 0 as greedy, but OpenVINO GenAI rejects a
+    non-positive temperature while do_sample is true, and that failure unloads
+    the model.
+    """
+    generation_config.temperature = temperature
+    if temperature <= 0:
+        generation_config.do_sample = False
+
+
 def generate_ov_scheduler_config(scheduler_config: SchedulerConfigSchema) -> dict:
   """Generates a SchedulerConfig object from the scheduler config model.
 
diff --git a/src/engine/ov_genai/vlm.py b/src/engine/ov_genai/vlm.py
index d6caf7d..392ac19 100644
--- a/src/engine/ov_genai/vlm.py
+++ b/src/engine/ov_genai/vlm.py
@@ -1,4 +1,7 @@
-from src.engine.ov_genai.utils import extract_scheduler_config_from_loader
+from src.engine.ov_genai.utils import (
+    apply_temperature,
+    extract_scheduler_config_from_loader,
+)
 import asyncio
 import base64
 import gc
@@ -415,7 +418,7 @@ def create_generation_config(self, config: OVGenAI_GenConfig) -> GenerationConfi
         """
         generation_kwargs = self.model_path.get_generation_config() if self.model_path else GenerationConfig()
         generation_kwargs.max_new_tokens = config.max_tokens
-        generation_kwargs.temperature = config.temperature
+        apply_temperature(generation_kwargs, config.temperature)
         generation_kwargs.top_k = config.top_k
         generation_kwargs.top_p = config.top_p
         generation_kwargs.repetition_penalty = config.repetition_penalty
diff --git a/src/server/schemas/modeling/contract_ovgenai_llm_and_vlm.py b/src/server/schemas/modeling/contract_ovgenai_llm_and_vlm.py
index 79fbbd8..700d867 100644
--- a/src/server/schemas/modeling/contract_ovgenai_llm_and_vlm.py
+++ b/src/server/schemas/modeling/contract_ovgenai_llm_and_vlm.py
@@ -53,7 +53,7 @@ class OVGenAI_GenConfig(BaseModel):
         description="Confidence threshold for accepting draft tokens (typically 0.3-0.5)"
     )
 
-    stream: bool = Field(
+    stream: Optional[bool] = Field(
         default=False,
         description="Stream output in chunks of tokens."
     )
diff --git a/tests/unit/test_config_merge_unit.py b/tests/unit/test_config_merge_unit.py
index ac545ca..4f0ba2c 100644
--- a/tests/unit/test_config_merge_unit.py
+++ b/tests/unit/test_config_merge_unit.py
@@ -244,3 +244,11 @@ def test_asr_yaml_default_yields_to_request() -> None:
     assert config.language == "Chinese"  # request wins
     assert config.max_chunk_sec == 25.0  # yaml default
     assert config.max_tokens == 1024  # engine default
+
+
+def test_stream_null_is_accepted() -> None:
+    # OpenAI-compatible clients send `stream: null`, and the chat route forwards
+    # request.stream (None when the client omits it); a bare `bool` field 400s.
+    config = build_config(OVGenAI_GenConfig, request={}, defaults={}, messages=[], stream=None)
+
+    assert not config.stream
diff --git a/tests/unit/test_ov_genai_llm_unit.py b/tests/unit/test_ov_genai_llm_unit.py
index 91433e7..b136e5f 100644
--- a/tests/unit/test_ov_genai_llm_unit.py
+++ b/tests/unit/test_ov_genai_llm_unit.py
@@ -269,3 +269,33 @@ async def test_unload_model_resets_state(monkeypatch: pytest.MonkeyPatch, load_c
     registry.register_unload.assert_called_once_with("model-name")
     gc_mock.assert_called_once()
 
+
+
+class DummyGenerationConfig:
+    pass
+
+
+def test_create_generation_config_zero_temperature_disables_sampling(
+    monkeypatch: pytest.MonkeyPatch, load_config: ModelLoadConfig
+) -> None:
+    monkeypatch.setattr(llm_module, "GenerationConfig", DummyGenerationConfig)
+    llm = OVGenAI_LLM(load_config)
+    llm.model = None
+
+    config = llm.create_generation_config(OVGenAI_GenConfig(temperature=0.0))
+
+    assert config.do_sample is False
+    assert config.temperature == 0.0
+
+
+def test_create_generation_config_positive_temperature_keeps_sampling(
+    monkeypatch: pytest.MonkeyPatch, load_config: ModelLoadConfig
+) -> None:
+    monkeypatch.setattr(llm_module, "GenerationConfig", DummyGenerationConfig)
+    llm = OVGenAI_LLM(load_config)
+    llm.model = None
+
+    config = llm.create_generation_config(OVGenAI_GenConfig(temperature=0.7))
+
+    assert getattr(config, "do_sample", None) is None
+    assert config.temperature == 0.7
diff --git a/tests/unit/test_ov_genai_vlm_unit.py b/tests/unit/test_ov_genai_vlm_unit.py
index 4e034f5..c29b28d 100644
--- a/tests/unit/test_ov_genai_vlm_unit.py
+++ b/tests/unit/test_ov_genai_vlm_unit.py
@@ -253,3 +253,20 @@ def test_resolve_prompt_strips_stray_token_for_text_only_chat(
     prompt, images = vlm._resolve_prompt_and_images(config)
     assert images == []
     assert tok not in prompt
+
+
+class DummyVlmGenerationConfig:
+    pass
+
+
+def test_vlm_create_generation_config_zero_temperature_disables_sampling(
+    monkeypatch: pytest.MonkeyPatch, load_config: ModelLoadConfig
+) -> None:
+    monkeypatch.setattr(vlm_module, "GenerationConfig", DummyVlmGenerationConfig)
+    vlm = OVGenAI_VLM(load_config)
+    vlm.model_path = None
+
+    config = vlm.create_generation_config(OVGenAI_GenConfig(temperature=0.0))
+
+    assert config.do_sample is False
+    assert config.temperature == 0.0