diff --git a/examples/multi_modal/advanced/cost_optimized_processing.py b/examples/multi_modal/advanced/cost_optimized_processing.py
index ae760e35..882e3271 100644
--- a/examples/multi_modal/advanced/cost_optimized_processing.py
+++ b/examples/multi_modal/advanced/cost_optimized_processing.py
@@ -5,10 +5,10 @@
 import asyncio
 import base64
 from pathlib import Path
-from typing import Dict, List, Optional
+from typing import Any, Dict, List, Optional
 
 from multimind.router.multi_modal_router import MultiModalRouter
-from multimind.models.advanced import CostOptimizedWrapper
+# from multimind.models.advanced import CostOptimizedWrapper
 from multimind.types import UnifiedRequest, ModalityInput, ModalityOutput
 from multimind.metrics.cost_tracker import CostTracker
 from multimind.metrics.performance import PerformanceTracker
@@ -100,6 +100,8 @@ def _get_cost_optimized_model(self, modality: str) -> str:
         
         # Get available models
         models = self.router.get_available_models(modality)
+        if not models:
+            return "default"
         
         # Get cost metrics
         cost_metrics = self.cost_tracker.get_modality_metrics(modality)
@@ -122,7 +124,7 @@ def _get_cost_optimized_model(self, modality: str) -> str:
                 best_score = score
                 best_model = model
         
-        return best_model or models[0]
+        return best_model or (models[0] if models else "default")
 
 
 async def main():
diff --git a/multimind/__pycache__/__init__.cpython-313.pyc b/multimind/__pycache__/__init__.cpython-313.pyc
index ee0afe1c..1e0cdcd0 100644
Binary files a/multimind/__pycache__/__init__.cpython-313.pyc and b/multimind/__pycache__/__init__.cpython-313.pyc differ
diff --git a/multimind/api/unified_api.py b/multimind/api/unified_api.py
index 6c6a1a55..dab2d180 100644
--- a/multimind/api/unified_api.py
+++ b/multimind/api/unified_api.py
@@ -3,37 +3,13 @@
 """
 
 from fastapi import FastAPI, HTTPException
-from pydantic import BaseModel, Field
-from typing import Dict, List, Any, Optional, Union
+from typing import Dict, Any
 import asyncio
 from ..models.moe import MoEFactory
+from ..types import UnifiedRequest, UnifiedResponse
 
 app = FastAPI(title="Unified Multi-Modal API")
 
-class ModalityInput(BaseModel):
-    """Input for a specific modality."""
-    content: Any
-    modality: str
-
-class UnifiedRequest(BaseModel):
-    """Unified request structure for multi-modal processing."""
-    inputs: List[ModalityInput]
-    use_moe: bool = Field(default=True, description="Whether to use MoE processing")
-    constraints: Optional[Dict[str, Any]] = Field(
-        default=None,
-        description="Processing constraints (cost, latency, etc.)"
-    )
-    workflow: Optional[str] = Field(
-        default=None,
-        description="Optional MCP workflow to use"
-    )
-
-class UnifiedResponse(BaseModel):
-    """Unified response structure."""
-    outputs: Dict[str, Any]
-    expert_weights: Optional[Dict[str, float]] = None
-    metrics: Dict[str, Any]
-
 # Initialize components
 try:
     moe_factory = MoEFactory()
diff --git a/multimind/metrics/__init__.py b/multimind/metrics/__init__.py
new file mode 100644
index 00000000..de01c9fd
--- /dev/null
+++ b/multimind/metrics/__init__.py
@@ -0,0 +1,12 @@
+"""
+Lightweight metrics utilities used by examples and SDK components.
+"""
+
+from .cost_tracker import CostTracker
+from .performance import PerformanceTracker
+
+__all__ = [
+    "CostTracker",
+    "PerformanceTracker",
+]
+
diff --git a/multimind/metrics/cost_tracker.py b/multimind/metrics/cost_tracker.py
new file mode 100644
index 00000000..c0c5b9dd
--- /dev/null
+++ b/multimind/metrics/cost_tracker.py
@@ -0,0 +1,87 @@
+"""
+Cost tracking helpers.
+
+The SDK has multiple cost/perf tracking implementations; this one is a small,
+stable surface used by examples (e.g. multi-modal cost optimization).
+"""
+
+from __future__ import annotations
+
+from typing import Any, Dict, DefaultDict
+from collections import defaultdict
+
+
+class CostTracker:
+    """
+    Tracks costs per (modality, model_id).
+
+    Expected example surface:
+    - get_modality_cost(modality, result) -> float
+    - get_modality_metrics(modality) -> dict[model_id] -> {"avg_cost", "total_cost", "count"}
+    """
+
+    def __init__(self) -> None:
+        # stats[modality][model_id] = {"total_cost": float, "count": int}
+        self._stats: DefaultDict[str, Dict[str, Dict[str, Any]]] = defaultdict(dict)
+
+    def _ensure(self, modality: str, model_id: str) -> Dict[str, Any]:
+        if model_id not in self._stats[modality]:
+            self._stats[modality][model_id] = {"total_cost": 0.0, "count": 0}
+        return self._stats[modality][model_id]
+
+    def get_modality_cost(self, modality: str, result: Any) -> float:
+        """
+        Extract + record cost for a modality result.
+
+        Heuristics:
+        - If result is a dict, read result["cost"] (default 0.0)
+        - model id is read from result["model_id"] or result["model"] (default "unknown")
+        """
+
+        model_id = "unknown"
+        cost = 0.0
+
+        data: Any = result
+        # Support Pydantic models (v1/v2) and plain objects
+        if hasattr(result, "model_dump"):
+            data = result.model_dump()
+        elif hasattr(result, "dict"):
+            try:
+                data = result.dict()
+            except Exception:
+                data = result
+
+        if isinstance(data, dict):
+            metadata = data.get("metadata") if isinstance(data.get("metadata"), dict) else {}
+            model_id = str(
+                data.get("model_id")
+                or data.get("model")
+                or metadata.get("model_id")
+                or "unknown"
+            )
+            try:
+                cost = float(data.get("cost") or metadata.get("cost") or 0.0)
+            except (TypeError, ValueError):
+                cost = 0.0
+
+        stat = self._ensure(modality, model_id)
+        stat["total_cost"] += cost
+        stat["count"] += 1
+
+        return cost
+
+    def get_modality_metrics(self, modality: str) -> Dict[str, Dict[str, Any]]:
+        """Return metrics keyed by model id."""
+
+        metrics: Dict[str, Dict[str, Any]] = {}
+        for model_id, stat in self._stats.get(modality, {}).items():
+            count = int(stat.get("count", 0)) or 0
+            total_cost = float(stat.get("total_cost", 0.0)) if count else 0.0
+            avg_cost = total_cost / count if count else 0.0
+            metrics[model_id] = {
+                "avg_cost": avg_cost,
+                "total_cost": total_cost,
+                "count": count,
+            }
+        return metrics
+
diff --git a/multimind/metrics/performance.py b/multimind/metrics/performance.py
new file mode 100644
index 00000000..46700f5b
--- /dev/null
+++ b/multimind/metrics/performance.py
@@ -0,0 +1,79 @@
+"""
+Performance tracking helpers.
+
+This module provides a small, stable API used by examples.
+"""
+
+from __future__ import annotations
+
+import time
+from typing import Any, Dict, DefaultDict
+from collections import defaultdict
+
+
+class PerformanceTracker:
+    """
+    Tracks latency/success per (modality, model_id).
+
+    Expected example surface:
+    - get_current_time() -> float
+    - track_latency(modality, latency) -> None
+    - track_error(modality, error) -> None
+    - get_modality_metrics(modality) -> dict[model_id] -> {"success_rate", "avg_latency"}
+    """
+
+    def __init__(self) -> None:
+        # stats[modality][model_id] = {"success": int, "fail": int, "lat_total": float, "lat_count": int}
+        self._stats: DefaultDict[str, Dict[str, Dict[str, Any]]] = defaultdict(dict)
+
+    def _ensure(self, modality: str, model_id: str) -> Dict[str, Any]:
+        if model_id not in self._stats[modality]:
+            self._stats[modality][model_id] = {
+                "success": 0,
+                "fail": 0,
+                "lat_total": 0.0,
+                "lat_count": 0,
+            }
+        return self._stats[modality][model_id]
+
+    def get_current_time(self) -> float:
+        return time.time()
+
+    def track_latency(self, modality: str, latency: float, model_id: str = "unknown", success: bool = True) -> None:
+        stat = self._ensure(modality, model_id)
+        if success:
+            stat["success"] += 1
+        else:
+            stat["fail"] += 1
+        try:
+            lat = float(latency)
+        except (TypeError, ValueError):
+            lat = 0.0
+        stat["lat_total"] += lat
+        stat["lat_count"] += 1
+
+    def track_error(self, modality: str, error: str, model_id: str = "unknown") -> None:
+        stat = self._ensure(modality, model_id)
+        stat["fail"] += 1
+
+    def track_success(self, modality: str, model_id: str = "unknown") -> None:
+        """Convenience method for recording a success without latency."""
+        stat = self._ensure(modality, model_id)
+        stat["success"] += 1
+
+    def get_modality_metrics(self, modality: str) -> Dict[str, Dict[str, Any]]:
+        metrics: Dict[str, Dict[str, Any]] = {}
+        for model_id, stat in self._stats.get(modality, {}).items():
+            success = int(stat.get("success", 0))
+            fail = int(stat.get("fail", 0))
+            total = success + fail
+            lat_count = int(stat.get("lat_count", 0))
+            lat_total = float(stat.get("lat_total", 0.0))
+            metrics[model_id] = {
+                "success_rate": (success / total) if total else 0.0,
+                "avg_latency": (lat_total / lat_count) if lat_count else 0.0,
+                "success": success,
+                "fail": fail,
+            }
+        return metrics
+
diff --git a/multimind/router/multi_modal_router.py b/multimind/router/multi_modal_router.py
index 5dabbdef..fed3e0b9 100644
--- a/multimind/router/multi_modal_router.py
+++ b/multimind/router/multi_modal_router.py
@@ -8,6 +8,7 @@
 from .router import ModelRouter
 from .strategy import RoutingStrategy
 from ..api.mcp.registry import WorkflowRegistry
+from ..types import ModalityInput, ModalityOutput
 
 class ModalityType:
     """Supported modality types."""
@@ -102,6 +103,65 @@ def register_modality_model(
         if modality not in self.modality_registry:
             self.modality_registry[modality] = {}
         self.modality_registry[modality][model_id] = model
+
+    def get_available_models(self, modality: str) -> List[str]:
+        """Return available model IDs for a modality."""
+        models = list(self.modality_registry.get(modality, {}).keys())
+        # Examples expect at least one model to pick from; provide a safe default.
+        return models or ["default"]
+
+    async def process_modality(
+        self,
+        input_data: ModalityInput,
+        model: Optional[str] = None,
+        **kwargs: Any
+    ) -> ModalityOutput:
+        """
+        Process a single modality input.
+
+        This is a compatibility method used by SDK examples. If a model_id is provided
+        and registered for that modality, we will call the model's `process()` method.
+        Otherwise we return a lightweight placeholder `ModalityOutput`.
+        """
+
+        modality = getattr(input_data, "modality", None) or "unknown"
+        content = getattr(input_data, "content", None)
+
+        model_id = model or "default"
+        model_obj: Optional[BaseLLM] = None
+        if modality in self.modality_registry and model:
+            model_obj = self.modality_registry[modality].get(model)
+
+        # If we have a real model, call it; otherwise return a placeholder output.
+        if model_obj is not None and hasattr(model_obj, "process"):
+            result = await model_obj.process(content, **kwargs)
+
+            # Heuristic mapping to ModalityOutput
+            if isinstance(result, dict):
+                out_content = result.get("content") or result.get("output") or result.get("text") or result
+                confidence = float(result.get("confidence") or 0.0) if "confidence" in result else 0.0
+                metadata = dict(result)
+                metadata.setdefault("model_id", model_id)
+                return ModalityOutput(
+                    content=out_content,
+                    modality=modality,
+                    confidence=confidence,
+                    metadata=metadata,
+                )
+
+            return ModalityOutput(
+                content=result,
+                modality=modality,
+                confidence=0.0,
+                metadata={"model_id": model_id},
+            )
+
+        return ModalityOutput(
+            content=f"[placeholder] processed {modality}",
+            modality=modality,
+            confidence=0.0,
+            metadata={"model_id": model_id, "note": "No registered model for modality"},
+        )
     
     async def _analyze_modalities(
         self,
diff --git a/multimind/types.py b/multimind/types.py
new file mode 100644
index 00000000..83c9ccbe
--- /dev/null
+++ b/multimind/types.py
@@ -0,0 +1,61 @@
+"""
+Shared type definitions for MultiMind (single contract module).
+
+All layers should import these models instead of redefining them:
+- API (FastAPI)
+- Router
+- MoE
+- Workflows
+- CLI / SDK examples
+"""
+
+from __future__ import annotations
+
+from typing import Any, Dict, List, Optional
+
+from pydantic import BaseModel, Field
+
+
+class ModalityInput(BaseModel):
+    """Input for a specific modality."""
+
+    content: Any
+    modality: str
+
+
+class ModalityOutput(BaseModel):
+    """Output for a specific modality.
+
+    Kept flexible (extra fields allowed) to support different backends.
+    """
+
+    content: Any = None
+    modality: Optional[str] = None
+    confidence: float = 0.0
+    metadata: Dict[str, Any] = Field(default_factory=dict)
+
+    model_config = {"extra": "allow"}
+
+
+class UnifiedRequest(BaseModel):
+    """Unified request structure for multi-modal processing."""
+
+    inputs: List[ModalityInput]
+    use_moe: bool = Field(default=True, description="Whether to use MoE processing")
+    constraints: Optional[Dict[str, Any]] = Field(
+        default=None,
+        description="Processing constraints (cost, latency, etc.)",
+    )
+    workflow: Optional[str] = Field(
+        default=None,
+        description="Optional MCP workflow to use",
+    )
+
+
+class UnifiedResponse(BaseModel):
+    """Unified response structure."""
+
+    outputs: Dict[str, Any]
+    expert_weights: Optional[Dict[str, float]] = None
+    metrics: Dict[str, Any] = Field(default_factory=dict)
+
diff --git a/tests/examples/multi_modal/test_cost_optimized_processing1.py b/tests/examples/multi_modal/test_cost_optimized_processing1.py
new file mode 100644
index 00000000..84ab53f1
--- /dev/null
+++ b/tests/examples/multi_modal/test_cost_optimized_processing1.py
@@ -0,0 +1,92 @@
+"""
+Lightweight tests for the cost-optimized multi-modal processing example.
+
+These tests are intentionally offline-safe:
+- they do not require API keys
+- they do not make network calls
+"""
+
+import sys
+from pathlib import Path
+import pytest
+
+from multimind.router.multi_modal_router import MultiModalRouter
+from multimind.types import UnifiedRequest, ModalityInput
+from multimind.metrics.cost_tracker import CostTracker
+from multimind.metrics.performance import PerformanceTracker
+
+# Import the example class under test
+REPO_ROOT = Path(__file__).resolve().parents[3]
+if str(REPO_ROOT) not in sys.path:
+    sys.path.insert(0, str(REPO_ROOT))
+from examples.multi_modal.advanced.cost_optimized_processing import CostOptimizedMultiModalProcessor
+
+
+@pytest.mark.asyncio
+async def test_placeholder_flow_cost_is_zero():
+    """
+    With no models registered, the MultiModalRouter returns placeholder outputs.
+    CostTracker should therefore record 0 cost.
+    """
+    router = MultiModalRouter()
+    cost_tracker = CostTracker()
+    performance_tracker = PerformanceTracker()
+
+    processor = CostOptimizedMultiModalProcessor(
+        router=router,
+        cost_tracker=cost_tracker,
+        performance_tracker=performance_tracker,
+        budget=1.0,
+    )
+
+    request = UnifiedRequest(
+        inputs=[
+            ModalityInput(modality="text", content="hello"),
+        ]
+    )
+
+    result = await processor.process_request(request, optimize_cost=True)
+    assert result["cost"] == 0.0
+    assert "text" in result["results"]
+
+@pytest.mark.asyncio
+async def test_placeholder_flow_image_audio_text_cost_is_zero():
+    """
+    With no models registered, image/audio/text modalities all use placeholder outputs.
+    This should still run end-to-end without network calls and record 0 cost.
+    """
+    router = MultiModalRouter()
+    cost_tracker = CostTracker()
+    performance_tracker = PerformanceTracker()
+
+    processor = CostOptimizedMultiModalProcessor(
+        router=router,
+        cost_tracker=cost_tracker,
+        performance_tracker=performance_tracker,
+        budget=1.0,
+    )
+
+    request = UnifiedRequest(
+        inputs=[
+            ModalityInput(modality="image", content="fake_image_base64"),
+            ModalityInput(modality="audio", content="fake_audio_base64"),
+            ModalityInput(modality="text", content="hello"),
+        ]
+    )
+
+    result = await processor.process_request(request, optimize_cost=True)
+    assert result["cost"] == 0.0
+    assert set(result["results"].keys()) == {"image", "audio", "text"}
+
+
+@pytest.mark.asyncio
+async def test_get_available_models_default_is_present():
+    """
+    The router should always return at least one model id so callers
+    don't crash with an empty list.
+    """
+    router = MultiModalRouter()
+    models = router.get_available_models("text")
+    assert isinstance(models, list)
+    assert len(models) >= 1
+