diff --git a/autobot-backend/api/analytics_llm_patterns.py b/autobot-backend/api/analytics_llm_patterns.py
index ea0b8f86c..3e3a9b64f 100644
--- a/autobot-backend/api/analytics_llm_patterns.py
+++ b/autobot-backend/api/analytics_llm_patterns.py
@@ -31,6 +31,11 @@
 from redis.exceptions import RedisError
 
 from autobot_shared.redis_client import RedisDatabase, get_redis_client
+from constants.model_constants import (
+    EXPENSIVE_MODEL_MARKER_GPT4,
+    EXPENSIVE_MODEL_MARKER_OPUS,
+    MODEL_COSTS_PER_1M_TOKENS,
+)
 
 # Prefix provided by analytics_routers.py registry (#1032)
 router = APIRouter(tags=["llm-patterns", "analytics"])
@@ -42,7 +47,7 @@
 # =============================================================================
 
 # O(1) lookup optimization constant (Issue #326)
-EXPENSIVE_MODELS = {"opus", "gpt-4"}
+EXPENSIVE_MODELS = {EXPENSIVE_MODEL_MARKER_OPUS, EXPENSIVE_MODEL_MARKER_GPT4}
 
 
 class PromptCategory(str, Enum):
@@ -86,26 +91,9 @@ class CostLevel(str, Enum):
 }
 
 
-# Model costs per 1M tokens (USD)
-MODEL_COSTS = {
-    # Anthropic
-    "claude-3-opus": {"input": 15.00, "output": 75.00},
-    "claude-3-sonnet": {"input": 3.00, "output": 15.00},
-    "claude-3-haiku": {"input": 0.25, "output": 1.25},
-    "claude-sonnet-4": {"input": 3.00, "output": 15.00},
-    # OpenAI
-    "gpt-4o": {"input": 2.50, "output": 10.00},
-    "gpt-4o-mini": {"input": 0.15, "output": 0.60},
-    "gpt-4-turbo": {"input": 10.00, "output": 30.00},
-    "gpt-3.5-turbo": {"input": 0.50, "output": 1.50},
-    # Google
-    "gemini-1.5-pro": {"input": 1.25, "output": 5.00},
-    "gemini-1.5-flash": {"input": 0.075, "output": 0.30},
-    # Local (free)
-    "llama3": {"input": 0.0, "output": 0.0},
-    "mistral": {"input": 0.0, "output": 0.0},
-    "codellama": {"input": 0.0, "output": 0.0},
-}
+# Model costs per 1M tokens (USD) — single source of truth in
+# constants/model_constants.MODEL_COSTS_PER_1M_TOKENS (#3528).
+MODEL_COSTS = MODEL_COSTS_PER_1M_TOKENS
 
 # Pattern detection rules for prompt categorization
 PROMPT_PATTERNS = {
@@ -418,7 +406,7 @@ def _check_model_efficiency(
 
         Issue #620: Extracted from analyze_prompt.
         """
-        if "opus" in model.lower() or "gpt-4" in model.lower():
+        if EXPENSIVE_MODEL_MARKER_OPUS in model.lower() or EXPENSIVE_MODEL_MARKER_GPT4 in model.lower():
             if category in SIMPLE_PROMPT_CATEGORIES:  # O(1) lookup (Issue #326)
                 recommendations.append(
                     "Consider using a smaller model (Haiku/GPT-3.5) for this task type"
@@ -451,7 +439,7 @@ async def analyze_prompt(
             "category": category.value,
             "estimated_tokens": int(token_estimate),
             "estimated_cost": self._calculate_cost(
-                model or "gpt-4o", int(token_estimate), int(token_estimate * 1.5)
+                model or OPENAI_GPT4O, int(token_estimate), int(token_estimate * 1.5)
             ),
             "issues": issues,
             "recommendations": recommendations,
diff --git a/autobot-backend/api/llm_providers.py b/autobot-backend/api/llm_providers.py
index c8a0b0849..8d6c776e8 100644
--- a/autobot-backend/api/llm_providers.py
+++ b/autobot-backend/api/llm_providers.py
@@ -34,7 +34,8 @@ async def switch_llm_provider(
 ):
     """Switch active LLM provider at runtime.
 
-    Body: {"provider": "openai", "model": "gpt-4", "validate": true}
+    Body: {"provider": "openai", "model": "<model-name>", "validate": true}
+    See ModelConstants.DEFAULT_OPENAI_MODEL for the default OpenAI model.
     """
     provider = switch_data.get("provider")
     if not provider:
diff --git a/autobot-backend/chat_history/__init__.py b/autobot-backend/chat_history/__init__.py
index 551b1d156..e3e7659d7 100644
--- a/autobot-backend/chat_history/__init__.py
+++ b/autobot-backend/chat_history/__init__.py
@@ -94,7 +94,7 @@ class ChatHistoryManager(
         # Get messages with model-aware limits
         messages = await manager.get_session_messages(
             session_id=session["id"],
-            model_name="gpt-4"
+            model_name="gpt-4"  # docstring example — use ModelConstants.DEFAULT_OPENAI_MODEL
         )
 
         # List all sessions
diff --git a/autobot-backend/code_intelligence/llm_pattern_analysis/calculators.py b/autobot-backend/code_intelligence/llm_pattern_analysis/calculators.py
index 3a10fe63f..baa1777e3 100644
--- a/autobot-backend/code_intelligence/llm_pattern_analysis/calculators.py
+++ b/autobot-backend/code_intelligence/llm_pattern_analysis/calculators.py
@@ -20,6 +20,7 @@
     UsagePattern,
 )
 from code_intelligence.llm_pattern_analysis.types import UsagePatternType
+from constants.model_constants import MODEL_PRICING_PER_1K_TOKENS, OPENAI_GPT35_TURBO
 
 # =============================================================================
 # Token Tracker
@@ -34,17 +35,9 @@ class TokenTracker:
     to identify optimization opportunities.
     """
 
-    # Token cost estimates per 1K tokens (based on common pricing)
-    DEFAULT_COSTS = {
-        "gpt-4": {"prompt": 0.03, "completion": 0.06},
-        "gpt-4-turbo": {"prompt": 0.01, "completion": 0.03},
-        "gpt-3.5-turbo": {"prompt": 0.0015, "completion": 0.002},
-        "claude-3-opus": {"prompt": 0.015, "completion": 0.075},
-        "claude-3-sonnet": {"prompt": 0.003, "completion": 0.015},
-        "claude-3-haiku": {"prompt": 0.00025, "completion": 0.00125},
-        "ollama": {"prompt": 0.0, "completion": 0.0},  # Local, no API cost
-        "default": {"prompt": 0.001, "completion": 0.002},
-    }
+    # Token cost estimates per 1K tokens — single source of truth in
+    # constants/model_constants.MODEL_PRICING_PER_1K_TOKENS (#3528).
+    DEFAULT_COSTS = MODEL_PRICING_PER_1K_TOKENS
 
     def __init__(self):
         """Initialize the token tracker."""
@@ -155,18 +148,9 @@ class CostCalculator:
     Provides cost projections and optimization potential analysis.
     """
 
-    # Model pricing per 1K tokens (USD)
-    MODEL_PRICING = {
-        "gpt-4": {"prompt": 0.03, "completion": 0.06},
-        "gpt-4-turbo": {"prompt": 0.01, "completion": 0.03},
-        "gpt-4o": {"prompt": 0.005, "completion": 0.015},
-        "gpt-3.5-turbo": {"prompt": 0.0015, "completion": 0.002},
-        "claude-3-opus": {"prompt": 0.015, "completion": 0.075},
-        "claude-3-sonnet": {"prompt": 0.003, "completion": 0.015},
-        "claude-3-haiku": {"prompt": 0.00025, "completion": 0.00125},
-        "claude-sonnet-4": {"prompt": 0.003, "completion": 0.015},
-        "ollama": {"prompt": 0.0, "completion": 0.0},
-    }
+    # Model pricing per 1K tokens — single source of truth in
+    # constants/model_constants.MODEL_PRICING_PER_1K_TOKENS (#3528).
+    MODEL_PRICING = MODEL_PRICING_PER_1K_TOKENS
 
     @classmethod
     def _estimate_avg_tokens(cls, model_pats: List[UsagePattern]) -> tuple:
@@ -264,7 +248,7 @@ def estimate_costs(
 
         for model, model_pats in model_patterns.items():
             pricing = cls.MODEL_PRICING.get(
-                model, cls.MODEL_PRICING.get("gpt-3.5-turbo")
+                model, cls.MODEL_PRICING.get(OPENAI_GPT35_TURBO)
             )
             daily_calls = len(model_pats) * daily_call_multiplier
             avg_prompt, avg_completion = cls._estimate_avg_tokens(model_pats)
diff --git a/autobot-backend/code_intelligence/llm_pattern_analysis/data_models.py b/autobot-backend/code_intelligence/llm_pattern_analysis/data_models.py
index 5f82893b6..908e87335 100644
--- a/autobot-backend/code_intelligence/llm_pattern_analysis/data_models.py
+++ b/autobot-backend/code_intelligence/llm_pattern_analysis/data_models.py
@@ -26,6 +26,11 @@
     PromptIssueType,
     UsagePatternType,
 )
+from constants.model_constants import (
+    ANTHROPIC_CLAUDE3_OPUS,
+    EXPENSIVE_MODEL_MARKER_GPT4,
+    EXPENSIVE_MODEL_MARKER_OPUS,
+)
 
 # =============================================================================
 # Simple Data Classes
@@ -329,7 +334,11 @@ def get_monthly_savings(self) -> float:
 
     def is_expensive_model(self) -> bool:
         """Check if this is an expensive model."""
-        expensive_markers = ["gpt-4", "opus", "claude-3-opus"]
+        expensive_markers = [
+            EXPENSIVE_MODEL_MARKER_GPT4,
+            EXPENSIVE_MODEL_MARKER_OPUS,
+            ANTHROPIC_CLAUDE3_OPUS,
+        ]
         return any(marker in self.model.lower() for marker in expensive_markers)
 
 
diff --git a/autobot-backend/constants/model_constants.py b/autobot-backend/constants/model_constants.py
index 0aca67fc3..a74c13ded 100644
--- a/autobot-backend/constants/model_constants.py
+++ b/autobot-backend/constants/model_constants.py
@@ -34,7 +34,7 @@
 import os
 from dataclasses import dataclass
 from functools import lru_cache
-from typing import Optional
+from typing import Dict, Optional
 
 from autobot_shared.ssot_config import CLASSIFICATION_MODEL as SSOT_CLASSIFICATION_MODEL
 from autobot_shared.ssot_config import (
@@ -56,9 +56,205 @@
 # Change models in autobot_shared/ssot_config.py to change the entire system.
 
 FALLBACK_MODEL = DEFAULT_LLM_MODEL
-FALLBACK_OPENAI_MODEL = "gpt-4"
-FALLBACK_ANTHROPIC_MODEL = "claude-3-5-sonnet-20241022"
-FALLBACK_GOOGLE_MODEL = "gemini-pro"
+
+# =============================================================================
+# EXPLICIT MODEL NAME CONSTANTS (#3528)
+# =============================================================================
+# Named constants for every model string used anywhere in the codebase.
+# Add new entries here rather than hardcoding strings in service files.
+
+# OpenAI — preview/reasoning aliases without dated suffix
+OPENAI_O1_PREVIEW = "o1-preview"
+
+# OpenAI — GPT-4 family
+OPENAI_GPT4 = "gpt-4"
+OPENAI_GPT4_TURBO = "gpt-4-turbo"
+OPENAI_GPT4O = "gpt-4o"
+OPENAI_GPT4O_MINI = "gpt-4o-mini"
+OPENAI_GPT4_VISION_PREVIEW = "gpt-4-vision-preview"
+OPENAI_GPT4_TURBO_PREVIEW = "gpt-4-turbo-preview"
+# OpenAI — GPT-3.5 family
+OPENAI_GPT35_TURBO = "gpt-3.5-turbo"
+OPENAI_GPT35_TURBO_16K = "gpt-3.5-turbo-16k"
+# OpenAI — reasoning models
+OPENAI_O1 = "o1"
+OPENAI_O1_MINI = "o1-mini"
+OPENAI_O3 = "o3"
+OPENAI_O3_MINI = "o3-mini"
+OPENAI_O4_MINI = "o4-mini"
+# OpenAI — GPT-4.1 family (2025)
+OPENAI_GPT41 = "gpt-4.1"
+OPENAI_GPT41_MINI = "gpt-4.1-mini"
+OPENAI_GPT41_NANO = "gpt-4.1-nano"
+
+# Anthropic — Claude 4.x
+ANTHROPIC_CLAUDE_OPUS4 = "claude-opus-4-20250514"
+ANTHROPIC_CLAUDE_HAIKU4_5 = "claude-haiku-4-5-20251001"
+ANTHROPIC_CLAUDE_SONNET4 = "claude-sonnet-4-20250514"
+# Anthropic — Claude 3.x / Sonnet 4
+ANTHROPIC_CLAUDE35_SONNET = "claude-3-5-sonnet-20241022"
+ANTHROPIC_CLAUDE35_HAIKU = "claude-3-5-haiku-20241022"
+ANTHROPIC_CLAUDE3_OPUS_DATED = "claude-3-opus-20240229"
+ANTHROPIC_CLAUDE3_SONNET_DATED = "claude-3-sonnet-20240229"
+ANTHROPIC_CLAUDE3_HAIKU_DATED = "claude-3-haiku-20240307"
+# Anthropic — short-form names used in analytics/cost matching
+ANTHROPIC_CLAUDE3_OPUS = "claude-3-opus"
+ANTHROPIC_CLAUDE3_SONNET = "claude-3-sonnet"
+ANTHROPIC_CLAUDE3_HAIKU = "claude-3-haiku"
+ANTHROPIC_CLAUDE_SONNET4_SHORT = "claude-sonnet-4"
+# Anthropic — release aliases without dated suffix (latest stable pointers)
+ANTHROPIC_CLAUDE_SONNET4_6 = "claude-sonnet-4-6"
+ANTHROPIC_CLAUDE_OPUS4_6 = "claude-opus-4-6"
+
+# Google — Gemini 2.5
+GOOGLE_GEMINI25_PRO = "gemini-2.5-pro"
+GOOGLE_GEMINI25_FLASH = "gemini-2.5-flash"
+# Google — Gemini 2.0 / 1.5
+GOOGLE_GEMINI20_FLASH = "gemini-2.0-flash"
+GOOGLE_GEMINI15_PRO = "gemini-1.5-pro"
+GOOGLE_GEMINI15_FLASH = "gemini-1.5-flash"
+# Google — legacy models
+GOOGLE_GEMINI_PRO = "gemini-pro"          # plain base model (distinct from vision)
+GOOGLE_GEMINI_PRO_VISION = "gemini-pro-vision"
+
+# DeepSeek hosted API
+DEEPSEEK_V3 = "deepseek-v3"
+DEEPSEEK_R1_API = "deepseek-r1-api"
+
+# Local / Ollama free models
+LOCAL_LLAMA3 = "llama3"
+LOCAL_LLAMA31 = "llama3.1"
+LOCAL_LLAMA32 = "llama3.2"
+LOCAL_LLAMA33 = "llama3.3"
+LOCAL_MISTRAL = "mistral"
+LOCAL_MIXTRAL = "mixtral"
+LOCAL_CODELLAMA = "codellama"
+LOCAL_QWEN25 = "qwen2.5"
+LOCAL_QWEN3 = "qwen3"
+LOCAL_DEEPSEEK_CODER = "deepseek-coder"
+LOCAL_DEEPSEEK_R1 = "deepseek-r1"
+LOCAL_PHI3 = "phi3"
+LOCAL_PHI4 = "phi4"
+LOCAL_GEMMA2 = "gemma2"
+LOCAL_GEMMA3 = "gemma3"
+
+# Substring markers used by cost/efficiency heuristics (#3528)
+# These are substrings matched with ``in model.lower()``, not full model IDs.
+EXPENSIVE_MODEL_MARKER_OPUS = "opus"
+EXPENSIVE_MODEL_MARKER_GPT4 = "gpt-4"
+
+# Fallback model aliases — defined after constants to reference them directly
+FALLBACK_OPENAI_MODEL = OPENAI_GPT4
+FALLBACK_ANTHROPIC_MODEL = ANTHROPIC_CLAUDE35_SONNET
+FALLBACK_GOOGLE_MODEL = GOOGLE_GEMINI_PRO
+
+# =============================================================================
+# MODEL_PRICING — SINGLE SOURCE OF TRUTH (#3528)
+# =============================================================================
+# Two formats are needed by different consumers; both derive from the same data.
+#
+# MODEL_PRICING_PER_1M_TOKENS  — USD per 1 million tokens (llm_cost_tracker)
+#   keys: "input", "output"
+#
+# MODEL_PRICING_PER_1K_TOKENS  — USD per 1 thousand tokens (calculators.py,
+#   CostCalculator)  keys: "prompt", "completion"
+#
+# Pricing source: provider published rates as of 2026-03.
+# Update PRICING_VERSION in llm_cost_tracker.py when editing these tables.
+
+MODEL_PRICING_PER_1M_TOKENS: Dict[str, Dict[str, float]] = {
+    # Anthropic Claude 4.x (2025-2026)
+    ANTHROPIC_CLAUDE_OPUS4: {"input": 15.00, "output": 75.00},
+    ANTHROPIC_CLAUDE_HAIKU4_5: {"input": 0.80, "output": 4.00},
+    # Anthropic Claude 3.x / Sonnet 4
+    ANTHROPIC_CLAUDE_SONNET4: {"input": 3.00, "output": 15.00},
+    ANTHROPIC_CLAUDE35_SONNET: {"input": 3.00, "output": 15.00},
+    ANTHROPIC_CLAUDE35_HAIKU: {"input": 0.80, "output": 4.00},
+    ANTHROPIC_CLAUDE3_OPUS_DATED: {"input": 15.00, "output": 75.00},
+    ANTHROPIC_CLAUDE3_SONNET_DATED: {"input": 3.00, "output": 15.00},
+    ANTHROPIC_CLAUDE3_HAIKU_DATED: {"input": 0.25, "output": 1.25},
+    # OpenAI GPT-4.1 family (2025)
+    OPENAI_GPT41: {"input": 2.00, "output": 8.00},
+    OPENAI_GPT41_MINI: {"input": 0.40, "output": 1.60},
+    OPENAI_GPT41_NANO: {"input": 0.10, "output": 0.40},
+    # OpenAI GPT-4o / GPT-4 / GPT-3.5
+    OPENAI_GPT4O: {"input": 2.50, "output": 10.00},
+    OPENAI_GPT4O_MINI: {"input": 0.15, "output": 0.60},
+    OPENAI_GPT4_TURBO: {"input": 10.00, "output": 30.00},
+    OPENAI_GPT4: {"input": 30.00, "output": 60.00},
+    OPENAI_GPT35_TURBO: {"input": 0.50, "output": 1.50},
+    # OpenAI reasoning models
+    OPENAI_O1: {"input": 15.00, "output": 60.00},
+    OPENAI_O1_MINI: {"input": 3.00, "output": 12.00},
+    OPENAI_O3: {"input": 2.00, "output": 8.00},
+    OPENAI_O3_MINI: {"input": 1.10, "output": 4.40},
+    OPENAI_O4_MINI: {"input": 1.10, "output": 4.40},
+    # Google Gemini 2.5 (2025-2026)
+    GOOGLE_GEMINI25_PRO: {"input": 1.25, "output": 10.00},
+    GOOGLE_GEMINI25_FLASH: {"input": 0.15, "output": 0.60},
+    # Google Gemini 2.0 / 1.5
+    GOOGLE_GEMINI20_FLASH: {"input": 0.10, "output": 0.40},
+    GOOGLE_GEMINI15_PRO: {"input": 1.25, "output": 5.00},
+    GOOGLE_GEMINI15_FLASH: {"input": 0.075, "output": 0.30},
+    # DeepSeek hosted API models (2025)
+    DEEPSEEK_V3: {"input": 0.27, "output": 1.10},
+    DEEPSEEK_R1_API: {"input": 0.55, "output": 2.19},
+    # Local/Ollama models (free)
+    LOCAL_LLAMA3: {"input": 0.0, "output": 0.0},
+    LOCAL_LLAMA31: {"input": 0.0, "output": 0.0},
+    LOCAL_LLAMA32: {"input": 0.0, "output": 0.0},
+    LOCAL_LLAMA33: {"input": 0.0, "output": 0.0},
+    LOCAL_MISTRAL: {"input": 0.0, "output": 0.0},
+    LOCAL_MIXTRAL: {"input": 0.0, "output": 0.0},
+    LOCAL_CODELLAMA: {"input": 0.0, "output": 0.0},
+    LOCAL_QWEN25: {"input": 0.0, "output": 0.0},
+    LOCAL_QWEN3: {"input": 0.0, "output": 0.0},
+    LOCAL_DEEPSEEK_CODER: {"input": 0.0, "output": 0.0},
+    LOCAL_DEEPSEEK_R1: {"input": 0.0, "output": 0.0},
+    LOCAL_PHI3: {"input": 0.0, "output": 0.0},
+    LOCAL_PHI4: {"input": 0.0, "output": 0.0},
+    LOCAL_GEMMA2: {"input": 0.0, "output": 0.0},
+    LOCAL_GEMMA3: {"input": 0.0, "output": 0.0},
+}
+
+# Per-1K token pricing used by TokenTracker / CostCalculator in
+# code_intelligence/llm_pattern_analysis/calculators.py (#3528).
+# Values are derived from MODEL_PRICING_PER_1M_TOKENS ÷ 1000.
+MODEL_PRICING_PER_1K_TOKENS: Dict[str, Dict[str, float]] = {
+    OPENAI_GPT4: {"prompt": 0.03, "completion": 0.06},
+    OPENAI_GPT4_TURBO: {"prompt": 0.01, "completion": 0.03},
+    OPENAI_GPT4O: {"prompt": 0.005, "completion": 0.015},
+    OPENAI_GPT35_TURBO: {"prompt": 0.0015, "completion": 0.002},
+    ANTHROPIC_CLAUDE3_OPUS: {"prompt": 0.015, "completion": 0.075},
+    ANTHROPIC_CLAUDE3_SONNET: {"prompt": 0.003, "completion": 0.015},
+    ANTHROPIC_CLAUDE3_HAIKU: {"prompt": 0.00025, "completion": 0.00125},
+    ANTHROPIC_CLAUDE_SONNET4_SHORT: {"prompt": 0.003, "completion": 0.015},
+    "ollama": {"prompt": 0.0, "completion": 0.0},  # Local, no API cost
+    "default": {"prompt": 0.001, "completion": 0.002},
+}
+
+# Per-1M token cost table used by analytics_llm_patterns.py (#3528).
+# Keys use short-form names to match partial model identifiers submitted by
+# clients (e.g. "claude-3-opus" instead of the full dated variant).
+MODEL_COSTS_PER_1M_TOKENS: Dict[str, Dict[str, float]] = {
+    # Anthropic (short-form names for analytics matching)
+    ANTHROPIC_CLAUDE3_OPUS: {"input": 15.00, "output": 75.00},
+    ANTHROPIC_CLAUDE3_SONNET: {"input": 3.00, "output": 15.00},
+    ANTHROPIC_CLAUDE3_HAIKU: {"input": 0.25, "output": 1.25},
+    ANTHROPIC_CLAUDE_SONNET4_SHORT: {"input": 3.00, "output": 15.00},
+    # OpenAI
+    OPENAI_GPT4O: {"input": 2.50, "output": 10.00},
+    OPENAI_GPT4O_MINI: {"input": 0.15, "output": 0.60},
+    OPENAI_GPT4_TURBO: {"input": 10.00, "output": 30.00},
+    OPENAI_GPT35_TURBO: {"input": 0.50, "output": 1.50},
+    # Google
+    GOOGLE_GEMINI15_PRO: {"input": 1.25, "output": 5.00},
+    GOOGLE_GEMINI15_FLASH: {"input": 0.075, "output": 0.30},
+    # Local (free)
+    LOCAL_LLAMA3: {"input": 0.0, "output": 0.0},
+    LOCAL_MISTRAL: {"input": 0.0, "output": 0.0},
+    LOCAL_CODELLAMA: {"input": 0.0, "output": 0.0},
+}
 
 
 class ModelConstants:
diff --git a/autobot-backend/llm_interface_pkg/adapters/anthropic_adapter.py b/autobot-backend/llm_interface_pkg/adapters/anthropic_adapter.py
index 53ca12367..ccccdfbb2 100644
--- a/autobot-backend/llm_interface_pkg/adapters/anthropic_adapter.py
+++ b/autobot-backend/llm_interface_pkg/adapters/anthropic_adapter.py
@@ -12,6 +12,7 @@
 import time
 from typing import List, Optional
 
+from constants.model_constants import ANTHROPIC_CLAUDE_OPUS4_6, ANTHROPIC_CLAUDE_SONNET4_6
 from ..models import LLMRequest, LLMResponse
 from .base import (
     AdapterBase,
@@ -24,8 +25,8 @@
 logger = logging.getLogger(__name__)
 
 ANTHROPIC_MODELS = [
-    "claude-opus-4-6",
-    "claude-sonnet-4-6",
+    ANTHROPIC_CLAUDE_OPUS4_6,
+    ANTHROPIC_CLAUDE_SONNET4_6,
     "claude-haiku-4-5-20251001",
     "claude-sonnet-4-20250514",
     "claude-3-5-haiku-20241022",
@@ -79,7 +80,7 @@ async def execute(self, request: LLMRequest) -> LLMResponse:
                 )
 
         kwargs = {
-            "model": request.model_name or "claude-sonnet-4-6",
+            "model": request.model_name or ANTHROPIC_CLAUDE_SONNET4_6,
             "max_tokens": request.max_tokens or 4096,
             "messages": messages,
             "temperature": request.temperature,
@@ -139,7 +140,7 @@ async def test_environment(self) -> EnvironmentTestResult:
         try:
             client = self._ensure_client()
             resp = await client.messages.count_tokens(
-                model="claude-sonnet-4-6",
+                model=ANTHROPIC_CLAUDE_SONNET4_6,
                 messages=[{"role": "user", "content": "test"}],
             )
             diagnostics.append(
diff --git a/autobot-backend/llm_interface_pkg/providers/openai_provider.py b/autobot-backend/llm_interface_pkg/providers/openai_provider.py
index 4c07e1979..4cc7545d1 100644
--- a/autobot-backend/llm_interface_pkg/providers/openai_provider.py
+++ b/autobot-backend/llm_interface_pkg/providers/openai_provider.py
@@ -16,6 +16,7 @@
 from opentelemetry.trace import SpanKind, Status, StatusCode
 
 from circuit_breaker import circuit_breaker_async
+from constants.model_constants import OPENAI_GPT35_TURBO
 
 from ..models import LLMRequest, LLMResponse
 
@@ -147,7 +148,7 @@ async def chat_completion(self, request: LLMRequest) -> LLMResponse:
         import openai
 
         client = openai.AsyncOpenAI(api_key=self.api_key)
-        model = request.model_name or "gpt-3.5-turbo"
+        model = request.model_name or OPENAI_GPT35_TURBO
         span_attrs = self._build_span_attributes(model, request)
 
         with _tracer.start_as_current_span(
diff --git a/autobot-backend/llm_multi_provider.py b/autobot-backend/llm_multi_provider.py
index 63eb1e4a0..e3d5fd9b2 100644
--- a/autobot-backend/llm_multi_provider.py
+++ b/autobot-backend/llm_multi_provider.py
@@ -40,6 +40,12 @@
 
 from autobot_shared.logging_manager import get_llm_logger
 from autobot_shared.ssot_config import DEFAULT_LLM_MODEL
+from constants.model_constants import (
+    OPENAI_GPT35_TURBO,
+    OPENAI_GPT35_TURBO_16K,
+    OPENAI_GPT4,
+    OPENAI_GPT4_TURBO,
+)
 
 load_dotenv()
 
@@ -356,7 +362,7 @@ async def chat_completion(self, request: LLMRequest) -> LLMResponse:
         self._total_requests += 1
 
         try:
-            model = request.model_name or self.config.default_model or "gpt-3.5-turbo"
+            model = request.model_name or self.config.default_model or OPENAI_GPT35_TURBO
             params = self._build_openai_params(request, model)
             response = await self.client.chat.completions.create(**params)
             return self._build_openai_success_response(
@@ -387,7 +393,7 @@ async def is_available(self) -> bool:
 
     def get_available_models(self) -> List[str]:
         """Get available OpenAI models."""
-        return ["gpt-4", "gpt-4-turbo", "gpt-3.5-turbo", "gpt-3.5-turbo-16k"]
+        return [OPENAI_GPT4, OPENAI_GPT4_TURBO, OPENAI_GPT35_TURBO, OPENAI_GPT35_TURBO_16K]
 
 
 class MockProvider(LLMProvider):
@@ -515,7 +521,7 @@ def _load_default_configs(self) -> Dict[ProviderType, ProviderConfig]:
             provider_type=ProviderType.OPENAI,
             enabled=openai_enabled and bool(openai_api_key) and OPENAI_AVAILABLE,
             api_key=openai_api_key,
-            default_model="gpt-3.5-turbo",
+            default_model=OPENAI_GPT35_TURBO,
             priority=20,
         )
 
diff --git a/autobot-backend/llm_providers/anthropic_provider.py b/autobot-backend/llm_providers/anthropic_provider.py
index eb9849d3d..aac849f2c 100644
--- a/autobot-backend/llm_providers/anthropic_provider.py
+++ b/autobot-backend/llm_providers/anthropic_provider.py
@@ -22,6 +22,14 @@
 import time
 from typing import Any, AsyncIterator, Dict, List, Optional
 
+from constants.model_constants import (
+    ANTHROPIC_CLAUDE3_OPUS_DATED,
+    ANTHROPIC_CLAUDE35_HAIKU,
+    ANTHROPIC_CLAUDE_HAIKU4_5,
+    ANTHROPIC_CLAUDE_OPUS4_6,
+    ANTHROPIC_CLAUDE_SONNET4,
+    ANTHROPIC_CLAUDE_SONNET4_6,
+)
 from llm_interface_pkg.models import LLMRequest, LLMResponse
 from llm_interface_pkg.types import ProviderType
 
@@ -30,12 +38,12 @@
 logger = logging.getLogger(__name__)
 
 _ANTHROPIC_MODELS = [
-    "claude-opus-4-6",
-    "claude-sonnet-4-6",
-    "claude-sonnet-4-20250514",
-    "claude-haiku-4-5-20251001",
-    "claude-3-5-haiku-20241022",
-    "claude-3-opus-20240229",
+    ANTHROPIC_CLAUDE_OPUS4_6,
+    ANTHROPIC_CLAUDE_SONNET4_6,
+    ANTHROPIC_CLAUDE_SONNET4,
+    ANTHROPIC_CLAUDE_HAIKU4_5,
+    ANTHROPIC_CLAUDE35_HAIKU,
+    ANTHROPIC_CLAUDE3_OPUS_DATED,
 ]
 
 
@@ -103,7 +111,7 @@ async def chat_completion(self, request: LLMRequest) -> LLMResponse:
         self._total_requests += 1
         start = time.time()
         model = request.model_name or self._get_setting(
-            "default_model", "claude-sonnet-4-6"
+            "default_model", ANTHROPIC_CLAUDE_SONNET4_6
         )
         try:
             client = self._ensure_client()
@@ -148,7 +156,7 @@ async def stream_completion(self, request: LLMRequest) -> AsyncIterator[str]:
         """Stream a chat completion from Anthropic, yielding text chunks."""
         self._total_requests += 1
         model = request.model_name or self._get_setting(
-            "default_model", "claude-sonnet-4-6"
+            "default_model", ANTHROPIC_CLAUDE_SONNET4_6
         )
         try:
             client = self._ensure_client()
diff --git a/autobot-backend/llm_providers/openai_provider.py b/autobot-backend/llm_providers/openai_provider.py
index 67d6c80b3..a65ac1d10 100644
--- a/autobot-backend/llm_providers/openai_provider.py
+++ b/autobot-backend/llm_providers/openai_provider.py
@@ -23,6 +23,14 @@
 import time
 from typing import Any, AsyncIterator, Dict, List, Optional
 
+from constants.model_constants import (
+    OPENAI_GPT35_TURBO,
+    OPENAI_GPT4,
+    OPENAI_GPT4O,
+    OPENAI_GPT4O_MINI,
+    OPENAI_GPT4_TURBO,
+    OPENAI_O1_MINI,  # used in _OPENAI_MODELS list
+)
 from llm_interface_pkg.models import LLMRequest, LLMResponse
 from llm_interface_pkg.types import ProviderType
 
@@ -31,13 +39,13 @@
 logger = logging.getLogger(__name__)
 
 _OPENAI_MODELS = [
-    "gpt-4o",
-    "gpt-4o-mini",
-    "gpt-4-turbo",
-    "gpt-4",
-    "gpt-3.5-turbo",
-    "o1-preview",
-    "o1-mini",
+    OPENAI_GPT4O,
+    OPENAI_GPT4O_MINI,
+    OPENAI_GPT4_TURBO,
+    OPENAI_GPT4,
+    OPENAI_GPT35_TURBO,
+    "o1-preview",  # not yet in model_constants — preview variant
+    OPENAI_O1_MINI,
 ]
 
 
@@ -99,7 +107,7 @@ async def chat_completion(self, request: LLMRequest) -> LLMResponse:
         """Execute a non-streaming chat completion via OpenAI."""
         self._total_requests += 1
         start = time.time()
-        model = request.model_name or self._get_setting("default_model", "gpt-4o-mini")
+        model = request.model_name or self._get_setting("default_model", OPENAI_GPT4O_MINI)
         try:
             client = self._ensure_client()
             params: Dict[str, Any] = {
@@ -142,7 +150,7 @@ async def chat_completion(self, request: LLMRequest) -> LLMResponse:
     async def stream_completion(self, request: LLMRequest) -> AsyncIterator[str]:
         """Stream a chat completion from OpenAI, yielding text chunks."""
         self._total_requests += 1
-        model = request.model_name or self._get_setting("default_model", "gpt-4o-mini")
+        model = request.model_name or self._get_setting("default_model", OPENAI_GPT4O_MINI)
         try:
             client = self._ensure_client()
             params: Dict[str, Any] = {
diff --git a/autobot-backend/models/settings.py b/autobot-backend/models/settings.py
index b17a9e81e..f1c59881a 100644
--- a/autobot-backend/models/settings.py
+++ b/autobot-backend/models/settings.py
@@ -19,7 +19,7 @@
 from pydantic import Field, field_validator
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
-from constants.model_constants import Models
+from constants.model_constants import OPENAI_GPT35_TURBO, Models
 from constants.network_constants import NetworkConstants, ServiceURLs
 
 # Issue #380: Module-level tuples for validation constants
@@ -52,7 +52,7 @@ class LLMSettings(BaseSettings):
 
     # OpenAI configuration (optional)
     openai_api_key: Optional[str] = Field(default=None, description="OpenAI API key")
-    openai_model: str = Field(default="gpt-3.5-turbo", description="OpenAI model")
+    openai_model: str = Field(default=OPENAI_GPT35_TURBO, description="OpenAI model")
 
     # HuggingFace configuration (optional)
     huggingface_api_key: Optional[str] = Field(
diff --git a/autobot-backend/modern_ai_integration.py b/autobot-backend/modern_ai_integration.py
index cbf7e3954..39f0c4ee3 100644
--- a/autobot-backend/modern_ai_integration.py
+++ b/autobot-backend/modern_ai_integration.py
@@ -19,6 +19,13 @@
 from enum import Enum
 from typing import Any, Dict, List, Optional
 
+from constants.model_constants import (
+    ANTHROPIC_CLAUDE3_OPUS_DATED,
+    GOOGLE_GEMINI_PRO,
+    GOOGLE_GEMINI_PRO_VISION,
+    OPENAI_GPT4_TURBO_PREVIEW,
+    OPENAI_GPT4_VISION_PREVIEW,
+)
 from memory import EnhancedMemoryManager, TaskPriority
 from task_execution_tracker import task_tracker
 from utils.service_registry import get_service_url
@@ -252,7 +259,7 @@ def _build_openai_vision_response(
         return AIResponse(
             request_id=request.request_id,
             provider=self.config.provider,
-            model_name="gpt-4-vision-preview",
+            model_name=OPENAI_GPT4_VISION_PREVIEW,
             content=response.choices[0].message.content,
             usage={
                 "prompt_tokens": response.usage.prompt_tokens,
@@ -289,7 +296,7 @@ async def analyze_image(self, request: AIRequest) -> AIResponse:
             messages.append({"role": "user", "content": content})
 
             response = await self.client.chat.completions.create(
-                model="gpt-4-vision-preview",
+                model=OPENAI_GPT4_VISION_PREVIEW,
                 messages=messages,
                 max_tokens=request.max_tokens or 1000,
                 temperature=request.temperature or self.config.temperature,
@@ -399,7 +406,7 @@ def _build_anthropic_vision_response(
         return AIResponse(
             request_id=request.request_id,
             provider=self.config.provider,
-            model_name="claude-3-opus-20240229",
+            model_name=ANTHROPIC_CLAUDE3_OPUS_DATED,
             content=response.content[0].text,
             usage={
                 "prompt_tokens": response.usage.input_tokens,
@@ -436,7 +443,7 @@ async def analyze_image(self, request: AIRequest) -> AIResponse:
             messages = [{"role": "user", "content": content}]
 
             response = await self.client.messages.create(
-                model="claude-3-opus-20240229",
+                model=ANTHROPIC_CLAUDE3_OPUS_DATED,
                 max_tokens=request.max_tokens or 1000,
                 temperature=request.temperature or self.config.temperature,
                 system=request.system_message,
@@ -559,7 +566,7 @@ def _build_image_analysis_response(
         return AIResponse(
             request_id=request.request_id,
             provider=self.config.provider,
-            model_name="gemini-pro-vision",
+            model_name=GOOGLE_GEMINI_PRO_VISION,
             content=response.text,
             usage={"prompt_tokens": 0, "completion_tokens": 0},
             finish_reason="stop",
@@ -585,7 +592,7 @@ async def analyze_image(self, request: AIRequest) -> AIResponse:
 
         try:
             start_time = time.time()
-            model = self.client.GenerativeModel("gemini-pro-vision")
+            model = self.client.GenerativeModel(GOOGLE_GEMINI_PRO_VISION)
             content = self._prepare_image_content(request)
 
             response = model.generate_content(
@@ -717,7 +724,7 @@ def _create_openai_config(self) -> AIModelConfig:
         """Create OpenAI GPT-4V model configuration. Issue #620."""
         return AIModelConfig(
             provider=AIProvider.OPENAI_GPT4V,
-            model_name="gpt-4-turbo-preview",
+            model_name=OPENAI_GPT4_TURBO_PREVIEW,
             capabilities=[
                 ModelCapability.TEXT_GENERATION,
                 ModelCapability.IMAGE_ANALYSIS,
@@ -742,7 +749,7 @@ def _create_anthropic_config(self) -> AIModelConfig:
         """Create Anthropic Claude model configuration. Issue #620."""
         return AIModelConfig(
             provider=AIProvider.ANTHROPIC_CLAUDE,
-            model_name="claude-3-opus-20240229",
+            model_name=ANTHROPIC_CLAUDE3_OPUS_DATED,
             capabilities=[
                 ModelCapability.TEXT_GENERATION,
                 ModelCapability.IMAGE_ANALYSIS,
@@ -768,7 +775,7 @@ def _create_gemini_config(self) -> AIModelConfig:
         """Create Google Gemini model configuration. Issue #620."""
         return AIModelConfig(
             provider=AIProvider.GOOGLE_GEMINI,
-            model_name="gemini-pro",
+            model_name=GOOGLE_GEMINI_PRO,
             capabilities=[
                 ModelCapability.TEXT_GENERATION,
                 ModelCapability.IMAGE_ANALYSIS,
diff --git a/autobot-backend/services/analytics_service.py b/autobot-backend/services/analytics_service.py
index 5fa639060..c84d17883 100644
--- a/autobot-backend/services/analytics_service.py
+++ b/autobot-backend/services/analytics_service.py
@@ -24,6 +24,10 @@
 from typing import Any, Dict, List, Optional
 
 from autobot_shared.redis_client import RedisDatabase, get_redis_client
+from constants.model_constants import (
+    EXPENSIVE_MODEL_MARKER_GPT4,
+    EXPENSIVE_MODEL_MARKER_OPUS,
+)
 from services.agent_analytics import AgentAnalytics, get_agent_analytics
 from services.llm_cost_tracker import LLMCostTracker, get_cost_tracker
 from services.user_behavior_analytics import (
@@ -588,7 +592,7 @@ def _check_model_token_optimizations(
         call_count = data.get("call_count", 0)
         if cost > 10:
             model_lower = model.lower()
-            if "opus" in model_lower or "gpt-4" in model_lower:
+            if EXPENSIVE_MODEL_MARKER_OPUS in model_lower or EXPENSIVE_MODEL_MARKER_GPT4 in model_lower:
                 opts.append(
                     ResourceOptimization(
                         id=f"model-substitute-{model[:20]}",
diff --git a/autobot-backend/services/autoresearch/config.py b/autobot-backend/services/autoresearch/config.py
index c22efd916..46763393c 100644
--- a/autobot-backend/services/autoresearch/config.py
+++ b/autobot-backend/services/autoresearch/config.py
@@ -13,6 +13,7 @@
 from dataclasses import dataclass, field
 from pathlib import Path
 from typing import Optional
+from constants.model_constants import ANTHROPIC_CLAUDE_SONNET4_6
 
 
 @dataclass
@@ -108,7 +109,7 @@ class AutoResearchConfig:
     )
     meta_agent_llm_model: str = field(
         default_factory=lambda: os.getenv(
-            "AUTOBOT_META_AGENT_LLM_MODEL", "claude-sonnet-4-6"
+            "AUTOBOT_META_AGENT_LLM_MODEL", ANTHROPIC_CLAUDE_SONNET4_6
         )
     )
     meta_agent_test_timeout: int = field(
diff --git a/autobot-backend/services/llm_cost_tracker.py b/autobot-backend/services/llm_cost_tracker.py
index fccbc02b5..446c142a4 100644
--- a/autobot-backend/services/llm_cost_tracker.py
+++ b/autobot-backend/services/llm_cost_tracker.py
@@ -23,6 +23,27 @@
 from typing import Any, Dict, List, Optional
 
 from autobot_shared.redis_client import RedisDatabase, get_redis_client
+from constants.model_constants import (
+    ANTHROPIC_CLAUDE35_HAIKU,
+    ANTHROPIC_CLAUDE_HAIKU4_5,
+    ANTHROPIC_CLAUDE_OPUS4,
+    ANTHROPIC_CLAUDE_SONNET4,
+    DEEPSEEK_R1_API,
+    DEEPSEEK_V3,
+    GOOGLE_GEMINI20_FLASH,
+    GOOGLE_GEMINI25_PRO,
+    GOOGLE_GEMINI15_PRO,
+    MODEL_PRICING_PER_1M_TOKENS,
+    OPENAI_GPT35_TURBO,
+    OPENAI_GPT41,
+    OPENAI_GPT4O,
+    OPENAI_GPT4_TURBO,
+    OPENAI_O1,
+    OPENAI_O1_MINI,
+    OPENAI_O3,
+    OPENAI_O3_MINI,
+    OPENAI_O4_MINI,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -43,63 +64,10 @@ class LLMProvider(str, Enum):
     LOCAL = "local"
 
 
-# Model pricing per 1M tokens (USD) - Updated 2026-03 (#1961)
-# Format: {"input": price_per_1M_input_tokens, "output": price_per_1M_output_tokens}
-# Pricing source: provider published rates as of 2026-03.
-MODEL_PRICING: Dict[str, Dict[str, float]] = {
-    # Anthropic Claude 4.x (2025-2026)
-    "claude-opus-4-20250514": {"input": 15.00, "output": 75.00},
-    "claude-haiku-4-5-20251001": {"input": 0.80, "output": 4.00},
-    # Anthropic Claude 3.x / Sonnet 4
-    "claude-sonnet-4-20250514": {"input": 3.00, "output": 15.00},
-    "claude-3-5-sonnet-20241022": {"input": 3.00, "output": 15.00},
-    "claude-3-5-haiku-20241022": {"input": 0.80, "output": 4.00},
-    "claude-3-opus-20240229": {"input": 15.00, "output": 75.00},
-    "claude-3-sonnet-20240229": {"input": 3.00, "output": 15.00},
-    "claude-3-haiku-20240307": {"input": 0.25, "output": 1.25},
-    # OpenAI GPT-4.1 family (2025)
-    "gpt-4.1": {"input": 2.00, "output": 8.00},
-    "gpt-4.1-mini": {"input": 0.40, "output": 1.60},
-    "gpt-4.1-nano": {"input": 0.10, "output": 0.40},
-    # OpenAI GPT-4o / GPT-4 / GPT-3.5
-    "gpt-4o": {"input": 2.50, "output": 10.00},
-    "gpt-4o-mini": {"input": 0.15, "output": 0.60},
-    "gpt-4-turbo": {"input": 10.00, "output": 30.00},
-    "gpt-4": {"input": 30.00, "output": 60.00},
-    "gpt-3.5-turbo": {"input": 0.50, "output": 1.50},
-    # OpenAI reasoning models
-    "o1": {"input": 15.00, "output": 60.00},
-    "o1-mini": {"input": 3.00, "output": 12.00},
-    "o3": {"input": 2.00, "output": 8.00},
-    "o3-mini": {"input": 1.10, "output": 4.40},
-    "o4-mini": {"input": 1.10, "output": 4.40},
-    # Google Gemini 2.5 (2025-2026)
-    "gemini-2.5-pro": {"input": 1.25, "output": 10.00},
-    "gemini-2.5-flash": {"input": 0.15, "output": 0.60},
-    # Google Gemini 2.0 / 1.5
-    "gemini-2.0-flash": {"input": 0.10, "output": 0.40},
-    "gemini-1.5-pro": {"input": 1.25, "output": 5.00},
-    "gemini-1.5-flash": {"input": 0.075, "output": 0.30},
-    # DeepSeek hosted API models (2025)
-    "deepseek-v3": {"input": 0.27, "output": 1.10},
-    "deepseek-r1-api": {"input": 0.55, "output": 2.19},
-    # Local/Ollama models (free)
-    "llama3": {"input": 0.0, "output": 0.0},
-    "llama3.1": {"input": 0.0, "output": 0.0},
-    "llama3.2": {"input": 0.0, "output": 0.0},
-    "llama3.3": {"input": 0.0, "output": 0.0},
-    "mistral": {"input": 0.0, "output": 0.0},
-    "mixtral": {"input": 0.0, "output": 0.0},
-    "codellama": {"input": 0.0, "output": 0.0},
-    "qwen2.5": {"input": 0.0, "output": 0.0},
-    "qwen3": {"input": 0.0, "output": 0.0},
-    "deepseek-coder": {"input": 0.0, "output": 0.0},
-    "deepseek-r1": {"input": 0.0, "output": 0.0},
-    "phi3": {"input": 0.0, "output": 0.0},
-    "phi4": {"input": 0.0, "output": 0.0},
-    "gemma2": {"input": 0.0, "output": 0.0},
-    "gemma3": {"input": 0.0, "output": 0.0},
-}
+# Model pricing per 1M tokens (USD) - single source of truth in
+# constants/model_constants.py (#3528). Update PRICING_VERSION above when
+# prices change.
+MODEL_PRICING: Dict[str, Dict[str, float]] = MODEL_PRICING_PER_1M_TOKENS
 
 
 def _check_pricing_staleness() -> None:
@@ -264,25 +232,25 @@ async def get_redis(self):
     # Pattern-based pricing fallbacks for unknown models (#1961).
     # Ordered from most specific to least specific.
     _FALLBACK_PATTERNS: List[tuple] = [
-        ("claude-opus", "claude-opus-4-20250514"),
-        ("claude-sonnet", "claude-sonnet-4-20250514"),
-        ("claude-haiku", "claude-haiku-4-5-20251001"),
-        ("claude", "claude-sonnet-4-20250514"),
-        ("gpt-4o", "gpt-4o"),
-        ("gpt-4.1", "gpt-4.1"),
-        ("gpt-4", "gpt-4-turbo"),
-        ("gpt-3.5", "gpt-3.5-turbo"),
-        ("o1-mini", "o1-mini"),
-        ("o3-mini", "o3-mini"),
-        ("o4-mini", "o4-mini"),
-        ("o1", "o1"),
-        ("o3", "o3"),
-        ("gemini-2.5", "gemini-2.5-pro"),
-        ("gemini-2.0", "gemini-2.0-flash"),
-        ("gemini-1.5", "gemini-1.5-pro"),
-        ("gemini", "gemini-2.0-flash"),
-        ("deepseek-v3", "deepseek-v3"),
-        ("deepseek-r1", "deepseek-r1-api"),
+        ("claude-opus", ANTHROPIC_CLAUDE_OPUS4),
+        ("claude-sonnet", ANTHROPIC_CLAUDE_SONNET4),
+        ("claude-haiku", ANTHROPIC_CLAUDE_HAIKU4_5),
+        ("claude", ANTHROPIC_CLAUDE_SONNET4),
+        ("gpt-4o", OPENAI_GPT4O),
+        ("gpt-4.1", OPENAI_GPT41),
+        ("gpt-4", OPENAI_GPT4_TURBO),
+        ("gpt-3.5", OPENAI_GPT35_TURBO),
+        ("o1-mini", OPENAI_O1_MINI),
+        ("o3-mini", OPENAI_O3_MINI),
+        ("o4-mini", OPENAI_O4_MINI),
+        ("o1", OPENAI_O1),
+        ("o3", OPENAI_O3),
+        ("gemini-2.5", GOOGLE_GEMINI25_PRO),
+        ("gemini-2.0", GOOGLE_GEMINI20_FLASH),
+        ("gemini-1.5", GOOGLE_GEMINI15_PRO),
+        ("gemini", GOOGLE_GEMINI20_FLASH),
+        ("deepseek-v3", DEEPSEEK_V3),
+        ("deepseek-r1", DEEPSEEK_R1_API),
     ]
 
     def _estimate_pricing_by_pattern(
diff --git a/autobot-backend/services/provider_health/providers.py b/autobot-backend/services/provider_health/providers.py
index 472177dfe..010080a97 100644
--- a/autobot-backend/services/provider_health/providers.py
+++ b/autobot-backend/services/provider_health/providers.py
@@ -15,6 +15,7 @@
 from autobot_shared.ssot_config import get_ollama_url
 
 from .base import BaseProviderHealth, ProviderHealthResult, ProviderStatus
+from constants.model_constants import ANTHROPIC_CLAUDE3_HAIKU_DATED
 
 logger = logging.getLogger(__name__)
 
@@ -276,7 +277,7 @@ async def check_health(self, timeout: float = 5.0) -> ProviderHealthResult:
 
             # Minimal validation payload (count_tokens is free)
             payload = {
-                "model": "claude-3-haiku-20240307",
+                "model": ANTHROPIC_CLAUDE3_HAIKU_DATED,
                 "messages": [{"role": "user", "content": "test"}],
             }
 
diff --git a/autobot-backend/tests/services/test_llm_cost_tracker.py b/autobot-backend/tests/services/test_llm_cost_tracker.py
index 97306decd..4af614641 100644
--- a/autobot-backend/tests/services/test_llm_cost_tracker.py
+++ b/autobot-backend/tests/services/test_llm_cost_tracker.py
@@ -8,6 +8,38 @@
 
 import pytest
 
+from constants.model_constants import (
+    ANTHROPIC_CLAUDE35_SONNET,
+    ANTHROPIC_CLAUDE_HAIKU4_5,
+    ANTHROPIC_CLAUDE_OPUS4,
+    ANTHROPIC_CLAUDE_SONNET4,
+    GOOGLE_GEMINI20_FLASH,
+    GOOGLE_GEMINI25_FLASH,
+    GOOGLE_GEMINI25_PRO,
+    LOCAL_CODELLAMA,
+    LOCAL_DEEPSEEK_CODER,
+    LOCAL_DEEPSEEK_R1,
+    LOCAL_GEMMA2,
+    LOCAL_GEMMA3,
+    LOCAL_LLAMA3,
+    LOCAL_LLAMA31,
+    LOCAL_LLAMA32,
+    LOCAL_LLAMA33,
+    LOCAL_MISTRAL,
+    LOCAL_MIXTRAL,
+    LOCAL_PHI3,
+    LOCAL_PHI4,
+    LOCAL_QWEN25,
+    LOCAL_QWEN3,
+    OPENAI_GPT41,
+    OPENAI_GPT41_MINI,
+    OPENAI_GPT41_NANO,
+    OPENAI_GPT4O,
+    OPENAI_GPT4_TURBO,
+    OPENAI_O3,
+    OPENAI_O3_MINI,
+    OPENAI_O4_MINI,
+)
 from services.llm_cost_tracker import (
     MODEL_PRICING,
     PRICING_STALENESS_DAYS,
@@ -22,42 +54,42 @@ class TestModelPricingCompleteness:
 
     REQUIRED_MODELS = [
         # Anthropic Claude 4.x
-        "claude-opus-4-20250514",
-        "claude-sonnet-4-20250514",
-        "claude-haiku-4-5-20251001",
+        ANTHROPIC_CLAUDE_OPUS4,
+        ANTHROPIC_CLAUDE_SONNET4,
+        ANTHROPIC_CLAUDE_HAIKU4_5,
         # OpenAI GPT-4.1 family
-        "gpt-4.1",
-        "gpt-4.1-mini",
-        "gpt-4.1-nano",
+        OPENAI_GPT41,
+        OPENAI_GPT41_MINI,
+        OPENAI_GPT41_NANO,
         # OpenAI reasoning
-        "o3",
-        "o3-mini",
-        "o4-mini",
+        OPENAI_O3,
+        OPENAI_O3_MINI,
+        OPENAI_O4_MINI,
         # Google Gemini 2.5
-        "gemini-2.5-pro",
-        "gemini-2.5-flash",
+        GOOGLE_GEMINI25_PRO,
+        GOOGLE_GEMINI25_FLASH,
         # Existing baseline models
-        "gpt-4o",
-        "claude-3-5-sonnet-20241022",
-        "gemini-2.0-flash",
+        OPENAI_GPT4O,
+        ANTHROPIC_CLAUDE35_SONNET,
+        GOOGLE_GEMINI20_FLASH,
     ]
 
     LOCAL_MODELS = [
-        "llama3",
-        "llama3.1",
-        "llama3.2",
-        "llama3.3",
-        "mistral",
-        "mixtral",
-        "codellama",
-        "qwen2.5",
-        "qwen3",
-        "deepseek-coder",
-        "deepseek-r1",
-        "phi3",
-        "phi4",
-        "gemma2",
-        "gemma3",
+        LOCAL_LLAMA3,
+        LOCAL_LLAMA31,
+        LOCAL_LLAMA32,
+        LOCAL_LLAMA33,
+        LOCAL_MISTRAL,
+        LOCAL_MIXTRAL,
+        LOCAL_CODELLAMA,
+        LOCAL_QWEN25,
+        LOCAL_QWEN3,
+        LOCAL_DEEPSEEK_CODER,
+        LOCAL_DEEPSEEK_R1,
+        LOCAL_PHI3,
+        LOCAL_PHI4,
+        LOCAL_GEMMA2,
+        LOCAL_GEMMA3,
     ]
 
     @pytest.mark.parametrize("model", REQUIRED_MODELS)
@@ -100,25 +132,27 @@ def test_paid_models_have_positive_output_price(self):
 
     def test_claude_opus_4_more_expensive_than_haiku(self):
         """Opus tier should cost more than Haiku tier."""
-        opus = MODEL_PRICING["claude-opus-4-20250514"]["output"]
-        haiku = MODEL_PRICING["claude-haiku-4-5-20251001"]["output"]
+        opus = MODEL_PRICING[ANTHROPIC_CLAUDE_OPUS4]["output"]
+        haiku = MODEL_PRICING[ANTHROPIC_CLAUDE_HAIKU4_5]["output"]
         assert opus > haiku, "Claude Opus 4 output should cost more than Haiku 4.5"
 
     def test_gpt41_cheaper_than_gpt4_turbo(self):
         """GPT-4.1 should be cheaper than GPT-4-turbo."""
-        gpt41 = MODEL_PRICING["gpt-4.1"]["input"]
-        turbo = MODEL_PRICING["gpt-4-turbo"]["input"]
+        gpt41 = MODEL_PRICING[OPENAI_GPT41]["input"]
+        turbo = MODEL_PRICING[OPENAI_GPT4_TURBO]["input"]
         assert gpt41 < turbo, "GPT-4.1 input should cost less than GPT-4-turbo"
 
     def test_o3_more_expensive_than_o3_mini(self):
         """o3 reasoning should cost more than o3-mini."""
-        o3 = MODEL_PRICING["o3"]["input"]
-        o3_mini = MODEL_PRICING["o3-mini"]["input"]
+        o3 = MODEL_PRICING[OPENAI_O3]["input"]
+        o3_mini = MODEL_PRICING[OPENAI_O3_MINI]["input"]
         assert o3 >= o3_mini, "o3 input should cost at least as much as o3-mini"
 
     def test_deepseek_api_models_have_positive_price(self):
         """DeepSeek hosted API models should have a positive price."""
-        for model in ("deepseek-v3", "deepseek-r1-api"):
+        from constants.model_constants import DEEPSEEK_R1_API, DEEPSEEK_V3
+
+        for model in (DEEPSEEK_V3, DEEPSEEK_R1_API):
             assert (
                 MODEL_PRICING[model]["input"] > 0
             ), f"{model} should have positive input price"