feat: allow default model to be set via DEEPEVAL_DEFAULT_MODEL env var

Adds DEEPEVAL_DEFAULT_MODEL setting that acts as a provider-agnostic
model fallback. GPTModel, AnthropicModel, GeminiModel, and OpenRouterModel
now read it when no model arg or provider-specific model env var is set,
before falling back to their hardcoded defaults.

Closes confident-ai#2602

Author: JKDasondee

deepeval/config/settings.py

@@ -303,6 +303,10 @@ def __setattr__(self, name: str, value):
         None,
         description="Identifier/tag to help identify your test run on Confident AI.",
     )
+    DEEPEVAL_DEFAULT_MODEL: Optional[str] = Field(
+        None,
+        description="Default model name used across all providers when no provider-specific model is set (e.g. 'gpt-4.1', 'claude-3-7-sonnet-latest').",
+    )
 
     #
     # Storage & Output

deepeval/models/llms/anthropic_model.py

@@ -58,7 +58,7 @@ def __init__(
         else:
             self.api_key = settings.ANTHROPIC_API_KEY
 
-        model = model or settings.ANTHROPIC_MODEL_NAME or default_model
+        model = model or settings.ANTHROPIC_MODEL_NAME or settings.DEEPEVAL_DEFAULT_MODEL or default_model
 
         if temperature is not None:
             temperature = float(temperature)

deepeval/models/llms/gemini_model.py

@@ -72,7 +72,7 @@ def __init__(
 
         settings = get_settings()
 
-        model = model or settings.GEMINI_MODEL_NAME or default_gemini_model
+        model = model or settings.GEMINI_MODEL_NAME or settings.DEEPEVAL_DEFAULT_MODEL or default_gemini_model
         self.model_data = GEMINI_MODELS_DATA.get(model)
 
         # Get API key from settings if not provided

deepeval/models/llms/openai_model.py

@@ -67,7 +67,7 @@ def __init__(
         if api_key is None and "api_key" in alias_values:
             api_key = alias_values["api_key"]
 
-        model = model or settings.OPENAI_MODEL_NAME
+        model = model or settings.OPENAI_MODEL_NAME or settings.DEEPEVAL_DEFAULT_MODEL
         if model is None:
             model = DEFAULT_GPT_MODEL
 

deepeval/models/llms/openrouter_model.py

@@ -80,7 +80,7 @@ def __init__(
         **kwargs,
     ):
         settings = get_settings()
-        model = model or settings.OPENROUTER_MODEL_NAME
+        model = model or settings.OPENROUTER_MODEL_NAME or settings.DEEPEVAL_DEFAULT_MODEL
         if model is None:
             model = DEFAULT_OPENROUTER_MODEL