diff --git a/synthetic_data_kit/models/llm_client.py b/synthetic_data_kit/models/llm_client.py
index 4f964100..07c3f9e3 100644
--- a/synthetic_data_kit/models/llm_client.py
+++ b/synthetic_data_kit/models/llm_client.py
@@ -12,6 +12,7 @@
 import logging
 import asyncio
 from pathlib import Path
+from concurrent.futures import ThreadPoolExecutor, as_completed
 
 from synthetic_data_kit.utils.config import load_config, get_vllm_config, get_openai_config, get_llm_provider
 
@@ -79,7 +80,7 @@ def __init__(self,
             self.max_retries = max_retries or api_endpoint_config.get('max_retries')
             self.retry_delay = retry_delay or api_endpoint_config.get('retry_delay')
             self.sleep_time = api_endpoint_config.get('sleep_time',0.5)
-            
+                        
             # Initialize OpenAI client
             self._init_openai_client()
         else:  # Default to vLLM
@@ -92,6 +93,9 @@ def __init__(self,
             self.max_retries = max_retries or vllm_config.get('max_retries')
             self.retry_delay = retry_delay or vllm_config.get('retry_delay')
             self.sleep_time = vllm_config.get('sleep_time',0.1)
+            self.max_concurrency = int(
+                os.environ.get("SDK_VLLM_MAX_CONCURRENCY", vllm_config.get("max_concurrency", 8))
+            )
             
             # No client to initialize for vLLM as we use requests directly
             # Verify server is running
@@ -533,6 +537,22 @@ async def process_batch():
         
         return results
     
+    def _vllm_post_once(self, request_data, verbose: bool) -> str:
+        """One /chat/completions call; returns the content string or raises."""
+        if verbose:
+            logger.info(f"Sending batch request to vLLM model {self.model}...")
+        response = requests.post(
+            f"{self.api_base}/chat/completions",
+            headers={"Content-Type": "application/json"},
+            data=json.dumps(request_data),
+            timeout=180,
+        )
+        if verbose:
+            logger.info(f"Received response with status code: {response.status_code}")
+        response.raise_for_status()
+        data = response.json()
+        return data["choices"][0]["message"]["content"]
+
     def _vllm_batch_completion(self,
                              message_batches: List[List[Dict[str, str]]],
                              temperature: float,
@@ -560,33 +580,27 @@ def _vllm_batch_completion(self,
                     "top_p": top_p
                 })
             
+            # Run requests concurrently while preserving order and isolating errors
+            max_workers = max(1, min(self.max_concurrency, len(batch_requests)))
+            batch_results = [""] * len(batch_requests)
             try:
-                # For now, we run these in parallel with multiple requests
-                batch_results = []
-                for request_data in batch_requests:
-                    # Only print if verbose mode is enabled
-                    if verbose:
-                        logger.info(f"Sending batch request to vLLM model {self.model}...")
-                    
-                    response = requests.post(
-                        f"{self.api_base}/chat/completions",
-                        headers={"Content-Type": "application/json"},
-                        data=json.dumps(request_data),
-                        timeout=180  # Increased timeout for batch processing
-                    )
-                    
-                    if verbose:
-                        logger.info(f"Received response with status code: {response.status_code}")
-                    
-                    response.raise_for_status()
-                    content = response.json()["choices"][0]["message"]["content"]
-                    batch_results.append(content)
-                
+                with ThreadPoolExecutor(max_workers=max_workers) as executor:
+                    future_to_index = {
+                        executor.submit(self._vllm_post_once, req, verbose): idx
+                        for idx, req in enumerate(batch_requests)
+                    }
+                    for future in as_completed(future_to_index):
+                        idx = future_to_index[future]
+                        try:
+                            batch_results[idx] = future.result()
+                        except Exception as e:
+                            # Don't fail the whole batch; record error in-place
+                            batch_results[idx] = f"ERROR: {e}"
                 results.extend(batch_results)
-                
-            except (requests.exceptions.RequestException, KeyError, IndexError) as e:
+            except Exception as e:
+                # If the executor itself failed for unexpected reasons
                 raise Exception(f"Failed to process vLLM batch: {str(e)}")
-            
+           
             # Small delay between batches
             if i + batch_size < len(message_batches):
                 time.sleep(self.sleep_time)
diff --git a/tests/unit/test_llm_client_hybrid.py b/tests/unit/test_llm_client_hybrid.py
new file mode 100644
index 00000000..2b6b52cb
--- /dev/null
+++ b/tests/unit/test_llm_client_hybrid.py
@@ -0,0 +1,191 @@
+import os
+import time
+import json
+import pytest
+import requests
+
+from synthetic_data_kit.models.llm_client import LLMClient
+
+# ---------- Live server detection helpers ----------
+
+def _live_base():
+    return os.getenv("LIVE_VLLM_BASE", "http://localhost:8000/v1")
+
+def _vllm_is_live(base: str, timeout=1.0) -> bool:
+    try:
+        r = requests.get(f"{base}/models", timeout=timeout)
+        return r.status_code == 200
+    except Exception:
+        return False
+
+@pytest.fixture(scope="session")
+def live_info():
+    base = _live_base()
+    return {"base": base, "up": _vllm_is_live(base)}
+
+# ---------- Live path (no mocks) ----------
+
+@pytest.mark.integration
+def test_live_vllm_smoke(live_info):
+    """
+    If a real vLLM server is reachable, run a real call.
+    Otherwise skip this test automatically.
+    """
+    if not live_info["up"]:
+        pytest.skip(f"No live vLLM at {_live_base()} — skipping live smoke.")
+
+    client = LLMClient(
+        provider="vllm",
+        api_base=live_info["base"],
+        model_name="TinyLlama/TinyLlama-1.1B-Chat-v1.0",  # must match the server's model
+        max_retries=2,
+        retry_delay=0.2,
+    )
+    out = client.chat_completion(
+        messages=[{"role": "user", "content": "Say 'pong' and nothing else."}],
+        temperature=0.0,
+        max_tokens=16,
+    )
+    assert isinstance(out, str)
+    assert "pong" in out.lower()
+
+# ---------- Mock path (runs when live is NOT available) ----------
+
+@pytest.fixture
+def patch_config(monkeypatch):
+    """
+    Force config -> provider=vllm and point to the default base.
+    """
+    def fake_load_config(_path=None):
+        return {
+            "llm": {"provider": "vllm"},
+            "vllm": {
+                "api_base": _live_base(),
+                "model": "fake-model",
+                "max_retries": 2,
+                "retry_delay": 0.05,
+                "sleep_time": 0.01,
+                "max_concurrency": 4,
+            },
+            "generation": {"temperature": 0.0, "max_tokens": 32, "top_p": 0.95, "batch_size": 8},
+        }
+    monkeypatch.setattr("synthetic_data_kit.models.llm_client.load_config", fake_load_config)
+    return fake_load_config
+
+@pytest.fixture
+def test_env(monkeypatch, live_info):
+    """
+    If live vLLM is DOWN, we stub _check_vllm_server and requests.post.
+    If live is UP, we do nothing (so the live smoke test can run).
+    """
+    if live_info["up"]:
+        # Live server exists; let the live test handle it.
+        return
+
+    # --- stub health check to "available" ---
+    def fake_check_vllm_server(self):
+        return True, {"models": [{"id": "fake-model"}]}
+    monkeypatch.setattr("synthetic_data_kit.models.llm_client.LLMClient._check_vllm_server", fake_check_vllm_server)
+
+    # --- stub POST /chat/completions to return deterministic JSON ---
+    def fake_post(url, headers=None, data=None, timeout=None):
+        body = json.loads(data or "{}")
+        # Simulate a small stagger so futures may complete out-of-order
+        time.sleep(0.01 if "slow" not in (headers or {}) else 0.02)
+
+        class Resp:
+            status_code = 200
+            def raise_for_status(self): pass
+            def json(self):
+                # Echo back the last user message content
+                msgs = body.get("messages", [])
+                content = next((m["content"] for m in reversed(msgs) if m.get("role") == "user"), "")
+                return {"choices": [{"message": {"content": f"echo:{content}"}}]}
+        return Resp()
+
+    monkeypatch.setattr("synthetic_data_kit.models.llm_client.requests.post", fake_post)
+
+
+# --- Tests that run under mocks when live server is not available ---
+
+@pytest.mark.unit
+def test_vllm_batch_completion_preserves_order(patch_config, test_env, live_info):
+    if live_info["up"]:
+        pytest.skip("Live vLLM detected; order test is only for the mock path.")
+
+    client = LLMClient(provider="vllm")  # config fixture supplies base/model
+    batches = [
+        [{"role": "user", "content": f"u{i}"}]
+        for i in range(5)
+    ]
+    out = client._vllm_batch_completion(
+        message_batches=batches,
+        temperature=0.0,
+        max_tokens=16,
+        top_p=0.95,
+        batch_size=5,
+        verbose=False,
+    )
+    assert out == [f"echo:u{i}" for i in range(5)]
+
+@pytest.mark.unit
+def test_vllm_batch_completion_isolates_errors(monkeypatch, patch_config, test_env, live_info):
+    if live_info["up"]:
+        pytest.skip("Live vLLM detected; error-isolation test is only for the mock path.")
+
+    # Patch one of the POSTs to raise
+    real_post = requests.post
+
+    def flaky_post(url, headers=None, data=None, timeout=None):
+        body = json.loads(data or "{}")
+        msgs = body.get("messages", [])
+        content = next((m["content"] for m in reversed(msgs) if m.get("role") == "user"), "")
+        if content == "boom":
+            raise requests.exceptions.ConnectionError("simulated failure")
+        return real_post(url, headers=headers, data=data, timeout=timeout)
+
+    monkeypatch.setattr("synthetic_data_kit.models.llm_client.requests.post", flaky_post)
+
+    client = LLMClient(provider="vllm")
+    batches = [
+        [{"role": "user", "content": "ok1"}],
+        [{"role": "user", "content": "boom"}],  # will fail
+        [{"role": "user", "content": "ok2"}],
+    ]
+    out = client._vllm_batch_completion(
+        message_batches=batches,
+        temperature=0.0,
+        max_tokens=16,
+        top_p=0.95,
+        batch_size=3,
+        verbose=False,
+    )
+    assert out[0].startswith("echo:ok1")
+    assert out[1].startswith("ERROR:")
+    assert out[2].startswith("echo:ok2")
+
+@pytest.mark.unit
+def test_vllm_batch_respects_max_concurrency(monkeypatch, patch_config, test_env, live_info):
+    if live_info["up"]:
+        pytest.skip("Live vLLM detected; concurrency test is only for the mock path.")
+
+    monkeypatch.setenv("SDK_VLLM_MAX_CONCURRENCY", "2")
+    client = LLMClient(provider="vllm")
+    assert client.max_concurrency == 2
+
+@pytest.mark.unit
+def test_vllm_post_once_happy_path(patch_config, test_env, live_info):
+    if live_info["up"]:
+        pytest.skip("Live vLLM detected; post-once test is only for the mock path.")
+
+    client = LLMClient(provider="vllm")
+    payload = {
+        "model": "fake-model",
+        "messages": [{"role": "user", "content": "xyz"}],
+        "temperature": 0.0,
+        "max_tokens": 8,
+        "top_p": 0.95,
+    }
+    out = client._vllm_post_once(payload, verbose=False)
+    assert out == "echo:xyz"
+