diff --git a/brevia/completions.py b/brevia/completions.py
index a751470..a9527d5 100644
--- a/brevia/completions.py
+++ b/brevia/completions.py
@@ -3,13 +3,14 @@
 from langchain.chains.llm import LLMChain
 from langchain_core.prompts.loading import load_prompt_from_config
 from pydantic import BaseModel
-from brevia.models import load_chatmodel
+from brevia.models import load_chatmodel, get_model_config
 from brevia.settings import get_settings
 
 
 class CompletionParams(BaseModel):
     """ Q&A basic conversation chain params """
     prompt: dict | None = None
+    config: dict | None = None
 
 
 def load_custom_prompt(prompt: dict | None):
@@ -28,10 +29,14 @@ def simple_completion_chain(
     """
 
     settings = get_settings()
-    llm_conf = settings.qa_completion_llm.copy()
-    comp_llm = load_chatmodel(llm_conf)
     verbose = settings.verbose_mode
-    # Create chain for follow-up question using chat history (if present)
+
+    llm_conf = get_model_config(
+        'qa_completion_llm',
+        user_config=completion_params.config,
+        default=settings.qa_completion_llm.copy()
+    )
+    comp_llm = load_chatmodel(llm_conf)
     completion_llm = LLMChain(
         llm=comp_llm,
         prompt=load_custom_prompt(completion_params.prompt),
diff --git a/brevia/models.py b/brevia/models.py
index df067c3..dd92b97 100644
--- a/brevia/models.py
+++ b/brevia/models.py
@@ -1,5 +1,6 @@
 """Utilities to create langchain LLM and Chat Model instances."""
 from abc import ABC, abstractmethod
+from glom import glom
 from typing import Any
 from langchain.chat_models.base import init_chat_model
 from langchain_core.embeddings import Embeddings
@@ -29,6 +30,32 @@ def get_token_ids(self, text: str) -> list[int]:
 }"""
 
 
+def get_model_config(
+    key: str,
+    user_config: dict | None = None,
+    db_metadata: dict | None = None,
+    default: object = None,
+) -> object:
+    """
+    Retrieve a model configuration value by searching in user config, db metadata,
+    and settings, in order. Uses glom for safe nested lookup.
+    """
+    # Check user config and db metadata
+    for source in [user_config, db_metadata]:
+        if source is not None:
+            value = glom(source, key, default=None)
+            if value is not None:
+                return value
+
+    # Check settings only if it's a known key
+    settings = get_settings()
+    if hasattr(settings, key):
+        value = getattr(settings, key)
+        return value.copy() if hasattr(value, "copy") else value
+
+    return default
+
+
 def load_llm(config: dict) -> BaseLLM:
     """Load langchain LLM, use Fake LLM in test mode"""
     if test_models_in_use():
diff --git a/brevia/query.py b/brevia/query.py
index 4c508d7..8f1f917 100644
--- a/brevia/query.py
+++ b/brevia/query.py
@@ -15,7 +15,7 @@
 from pydantic import BaseModel
 from brevia.connection import connection_string
 from brevia.collections import single_collection_by_name
-from brevia.models import load_chatmodel, load_embeddings
+from brevia.models import load_chatmodel, load_embeddings, get_model_config
 from brevia.prompts import load_qa_prompt, load_condense_prompt
 from brevia.settings import get_settings
 from brevia.utilities.types import load_type
@@ -67,6 +67,7 @@ class ChatParams(BaseModel):
     filter: dict[str, str | dict] | None = None
     source_docs: bool = False
     multiquery: bool = False
+    config: dict | None = None
     search_type: str = "similarity"
     score_threshold: float = 0.0
 
@@ -217,6 +218,8 @@ def conversation_rag_chain(
             - search_type (str): Type of search algorithm to use (def is 'similarity').
             - score_threshold (float): Threshold for filtering documents based on
               relevance scores (default is 0.0).
+            - config (dict | None): Optional configuration dict that can contain
+              completion_llm and followup_llm configs to override defaults.
         answer_callbacks (list[BaseCallbackHandler] | None): List of callback handlers
             for the final LLM answer to enable streaming (default is None).
 
@@ -232,10 +235,11 @@ def conversation_rag_chain(
     prompts = collection.cmetadata.get('prompts', {})
     prompts = prompts if prompts else {}
 
-    # Main LLM configuration
-    qa_llm_conf = collection.cmetadata.get(
+    # Main LLM configuration using get_model_config
+    qa_llm_conf = get_model_config(
         'qa_completion_llm',
-        dict(settings.qa_completion_llm).copy()
+        user_config=chat_params.config,
+        db_metadata=collection.cmetadata
     )
     qa_llm_conf['callbacks'] = [] if answer_callbacks is None else answer_callbacks
     qa_llm_conf['streaming'] = chat_params.streaming
@@ -248,10 +252,11 @@ def conversation_rag_chain(
         llm=chatllm
     )
 
-    # Chain to rewrite question with history
-    fup_llm_conf = collection.cmetadata.get(
+    # Chain to rewrite question with history using get_model_config
+    fup_llm_conf = get_model_config(
         'qa_followup_llm',
-        dict(settings.qa_followup_llm).copy()
+        user_config=chat_params.config,
+        db_metadata=collection.cmetadata
     )
     fup_llm = load_chatmodel(fup_llm_conf)
     fup_chain = (
@@ -292,10 +297,13 @@ def conversation_chain(
     collection or dataset.
     """
 
-    settings = get_settings()
-
     # Chain to rewrite question with history
-    fup_llm_conf = dict(settings.qa_followup_llm).copy()
+    # Check if followup_llm config is provided in chat_params
+    fup_llm_conf = get_model_config(
+        'qa_followup_llm',
+        user_config=chat_params.config
+    )
+
     fup_llm = load_chatmodel(fup_llm_conf)
     fup_chain = (
         load_condense_prompt()
@@ -303,7 +311,13 @@ def conversation_chain(
         | StrOutputParser()
     )
 
-    llm_conf = dict(settings.qa_completion_llm).copy()
+    # Main LLM configuration
+    # Check if completion_llm config is provided in chat_params
+    llm_conf = get_model_config(
+        'qa_completion_llm',
+        user_config=chat_params.config
+    )
+
     llm_conf['callbacks'] = [] if answer_callbacks is None else answer_callbacks
     llm_conf['streaming'] = chat_params.streaming
 
diff --git a/brevia/routers/completion_router.py b/brevia/routers/completion_router.py
index a0085a5..b3e120c 100644
--- a/brevia/routers/completion_router.py
+++ b/brevia/routers/completion_router.py
@@ -14,6 +14,7 @@ class CompletionBody(CompletionParams):
     """ /completion request body """
     text: str
     prompt: dict | None = None
+    config: dict | None = None
     token_data: bool = False
 
 
diff --git a/brevia/routers/qa_router.py b/brevia/routers/qa_router.py
index 0b35864..2a1b142 100644
--- a/brevia/routers/qa_router.py
+++ b/brevia/routers/qa_router.py
@@ -1,8 +1,8 @@
 """API endpoints for question answering and search"""
 import asyncio
-from glom import glom
 from typing import Annotated
 from typing_extensions import Self
+from glom import glom
 from pydantic import Field, model_validator
 from langchain.callbacks import AsyncIteratorCallbackHandler
 from langchain.chains.base import Chain
@@ -39,6 +39,7 @@ class ChatBody(ChatParams):
     collection: str | None = None
     chat_history: list = []
     chat_lang: str | None = None
+    config: dict | None = None
     mode: str = Field(pattern='^(rag|conversation)$', default='rag')
     token_data: bool = False
 
diff --git a/tests/test_completions.py b/tests/test_completions.py
index 13f515c..cb11caf 100644
--- a/tests/test_completions.py
+++ b/tests/test_completions.py
@@ -1,6 +1,7 @@
 """Query module tests"""
 from langchain.chains.base import Chain
 from brevia.completions import simple_completion_chain, CompletionParams
+from brevia.models import get_model_config
 
 
 fake_prompt = CompletionParams()
@@ -16,3 +17,43 @@ def test_simple_completion_chain():
     result = simple_completion_chain(fake_prompt)
     assert result is not None
     assert isinstance(result, Chain)
+
+
+def test_get_model_config():
+    """Test get_model_config functionality"""
+    # Test data using qa_completion_llm which exists in settings
+    test_key = "qa_completion_llm"
+    test_user_config = {
+        "qa_completion_llm": {"model": "from_user"}
+    }
+    test_db_config = {
+        "qa_completion_llm": {"model": "from_db"}
+    }
+    test_default = {"model": "default"}
+
+    # Test user config priority
+    result = get_model_config(
+        test_key,
+        user_config=test_user_config,
+        db_metadata=test_db_config,
+        default=test_default
+    )
+    assert result == {"model": "from_user"}
+
+    # Test db config fallback
+    result = get_model_config(
+        test_key,
+        user_config=None,
+        db_metadata=test_db_config,
+        default=test_default
+    )
+    assert result == {"model": "from_db"}
+
+    # Test default fallback when key not in settings
+    result = get_model_config(
+        "non_existent_key",
+        user_config=None,
+        db_metadata=None,
+        default=test_default
+    )
+    assert result == test_default