diff --git a/README.md b/README.md
index 569daa2..3bd92ed 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,70 @@ See [`SPEC.md`](SPEC.md).
 pip install -e .
 ```
 
+### Nvidia CUDA install
+
+If a node has an Nvidia GPU, it must install a CUDA-enabled PyTorch build. If you see:
+
+```text
+Torch not compiled with CUDA enabled
+```
+
+then the node installed the CPU-only PyTorch package.
+
+Recommended fix on a macOS/Linux Nvidia node:
+
+```bash
+source .venv/bin/activate
+pip uninstall -y torch torchvision torchaudio
+pip install --index-url https://download.pytorch.org/whl/cu121 torch torchvision torchaudio
+pip install -e .
+```
+
+Recommended fix on a Windows Nvidia node using PowerShell:
+
+```powershell
+.\.venv\Scripts\Activate.ps1
+python -m pip uninstall -y torch torchvision torchaudio
+python -m pip install --index-url https://download.pytorch.org/whl/cu121 torch torchvision torchaudio
+python -m pip install -e .
+```
+
+If PowerShell blocks venv activation, run this once in the same PowerShell window:
+
+```powershell
+Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass
+.\.venv\Scripts\Activate.ps1
+```
+
+Windows Command Prompt alternative:
+
+```bat
+.venv\Scripts\activate.bat
+python -m pip uninstall -y torch torchvision torchaudio
+python -m pip install --index-url https://download.pytorch.org/whl/cu121 torch torchvision torchaudio
+python -m pip install -e .
+```
+
+For newer CUDA builds, PyTorch may also provide `cu124` or `cu126` wheels. Check https://pytorch.org/get-started/locally/ if `cu121` is not appropriate.
+
+Verify CUDA support:
+
+```bash
+python - <<'PY'
+import torch
+print('torch:', torch.__version__)
+print('cuda available:', torch.cuda.is_available())
+print('cuda version:', torch.version.cuda)
+print('gpu:', torch.cuda.get_device_name(0) if torch.cuda.is_available() else None)
+PY
+```
+
+Then run the node with:
+
+```bash
+truecluster node --cluster-host YOUR_CLUSTER_IP --cluster-port 7001 --device cuda:0
+```
+
 ## Run a cluster
 
 ```bash
diff --git a/truecluster/cluster/api.py b/truecluster/cluster/api.py
index 5b399cd..c62548b 100644
--- a/truecluster/cluster/api.py
+++ b/truecluster/cluster/api.py
@@ -52,8 +52,21 @@ def create_app(runtime: ClusterRuntime) -> FastAPI:
             ],
         }
 
+    def _validate_model(requested: str | None) -> None:
+        if requested and requested != runtime.model_store.model_id:
+            raise HTTPException(
+                status_code=400,
+                detail={
+                    "error": {
+                        "message": f"requested model {requested!r} does not match loaded model {runtime.model_store.model_id!r}",
+                        "type": "model_mismatch",
+                    }
+                },
+            )
+
     @app.post("/v1/completions")
     async def completions(req: CompletionRequest) -> dict[str, Any]:
+        _validate_model(req.model)
         if req.stream:
             raise HTTPException(status_code=400, detail={"error": {"message": "streaming is not implemented", "type": "unsupported"}})
         prompt = req.prompt[0] if isinstance(req.prompt, list) else req.prompt
@@ -90,11 +103,13 @@ def create_app(runtime: ClusterRuntime) -> FastAPI:
 
     @app.post("/v1/chat/completions")
     async def chat_completions(req: ChatCompletionRequest) -> dict[str, Any]:
+        _validate_model(req.model)
         if req.stream:
             raise HTTPException(status_code=400, detail={"error": {"message": "streaming is not implemented", "type": "unsupported"}})
         tokenizer = runtime.model_store.tokenizer
         messages = [m.dict() for m in req.messages]
-        if hasattr(tokenizer, "apply_chat_template") and tokenizer.chat_template:
+        used_chat_template = bool(hasattr(tokenizer, "apply_chat_template") and tokenizer.chat_template)
+        if used_chat_template:
             prompt = tokenizer.apply_chat_template(messages, tokenize=False, add_generation_prompt=True)
         else:
             prompt = "\n".join(f"{m['role']}: {m['content']}" for m in messages) + "\nassistant:"
@@ -105,6 +120,7 @@ def create_app(runtime: ClusterRuntime) -> FastAPI:
                 temperature=req.temperature,
                 top_p=req.top_p,
                 stop=req.stop,
+                add_special_tokens=not used_chat_template,
             )
         except RuntimeError as exc:
             raise HTTPException(status_code=503, detail={"error": {"message": str(exc), "type": "cluster_not_ready"}}) from exc
diff --git a/truecluster/cluster/server.py b/truecluster/cluster/server.py
index 61f5451..35e8ca8 100644
--- a/truecluster/cluster/server.py
+++ b/truecluster/cluster/server.py
@@ -154,6 +154,7 @@ class ClusterRuntime:
         temperature: float = 0.7,
         top_p: float = 0.95,
         stop: str | list[str] | None = None,
+        add_special_tokens: bool = True,
     ) -> dict[str, Any]:
         from truecluster.cluster.sampler import sample_next_token
 
@@ -163,7 +164,7 @@ class ClusterRuntime:
             await self.clear_caches()
             request_id = f"req-{uuid.uuid4().hex}"
             tokenizer = self.model_store.tokenizer
-            encoded = tokenizer(prompt, return_tensors="pt", add_special_tokens=True)
+            encoded = tokenizer(prompt, return_tensors="pt", add_special_tokens=add_special_tokens)
             input_ids = encoded["input_ids"].to(torch.long)
             prompt_tokens = int(input_ids.shape[1])