diff --git a/src/brdata_rag_tools/models.py b/src/brdata_rag_tools/models.py
index e014ffd..8523df4 100644
--- a/src/brdata_rag_tools/models.py
+++ b/src/brdata_rag_tools/models.py
@@ -2,7 +2,7 @@
 import os
 from enum import Enum
 import tiktoken
-from typing import List
+from typing import Optional
 from openai import OpenAI
 import requests
 
@@ -17,8 +17,28 @@ class LLMName(Enum):
     IGEL = "igel"
     BISON001 = "text-bison@001"
 
+    @staticmethod
+    def openai_models() -> list["LLMName"]:
+        """Return a list of available OpenAI models."""
+        return [
+            LLMName.GPT35TURBO,
+            LLMName.GPT35TURBO0613,
+            LLMName.GPT35TURBO1106,
+            LLMName.GPT40314,
+            LLMName.GPT40613,
+            LLMName.GPT4,
+        ]
+
+    @staticmethod
+    def google_models() -> list["LLMName"]:
+        """Return a list of available Google models."""
+        return [
+            LLMName.BISON001
+        ]
+
     @property
     def max_input_tokens(self) -> int:
+        """Return context window size for the particular LLM."""
         if self in [LLMName.GPT35TURBO0613, LLMName.GPT35TURBO]:
             return 4096
         elif self in [LLMName.GPT4, LLMName.GPT40314, LLMName.GPT40613, LLMName.IGEL, LLMName.BISON001]:
@@ -30,6 +50,28 @@ def max_input_tokens(self) -> int:
             logging.warning(f"Unknown context window size for LLM {self}. Opt for default context window size of 2048.")
             return 2048
 
+    @property
+    def auth_token(self) -> str:
+        """Return the authentication token for the particular LLM."""
+        if self in LLMName.openai_models():
+            token = os.environ.get("OPENAI_TOKEN")
+        elif self == LLMName.IGEL:
+            token = os.environ.get("IGEL_TOKEN")
+        elif self in LLMName.google_models():
+            token = os.environ.get("GOOGLE_TOKEN")
+        else:
+            raise ValueError(f"No auth_token provided for model {self.value}.")
+        
+        if token is None:
+            raise EnvironmentError(
+                (
+                    f"Please set enviornment variable for model {self.value}. "
+                    f"See README for more information."
+                )
+            )
+
+        return token
+
 
 class Generator:
     """
@@ -74,19 +116,18 @@ class Generator:
     """
 
     def __init__(self,
-                 model: LLMName,
-                 auth_token: str = None,
-                 temperature: float = None,
-                 max_new_tokens: int = None,
-                 top_p: float = None,
-                 top_k: int = None,
-                 length_penalty: float = None,
-                 number_of_responses: int = None,
-                 max_token_length: int = None
-                 ):
-
+        model: LLMName,
+        auth_token: str = None,
+        temperature: float = None,
+        max_new_tokens: int = None,
+        top_p: float = None,
+        top_k: int = None,
+        length_penalty: float = None,
+        number_of_responses: int = None,
+        max_token_length: int = None
+    ):
         self.model: LLMName = model
-        self.auth_token: str = self.get_token(auth_token)
+        self.auth_token: str = auth_token or self.model.auth_token
         self.temperature: float = temperature
         self.max_new_tokens: int = max_new_tokens
         self.top_p: float = top_p
@@ -95,31 +136,6 @@ def __init__(self,
         self.number_of_responses = number_of_responses
         self.max_token_length: int = max_token_length
 
-    def get_token(self, token: str) -> str:
-        """
-        Returns the given auth_token or retrieves the appropriate auth_token based on the model value.
-
-        :param token: The auth_token to be used for authentication.
-        :type token: str
-        :return: The retrieved auth_token or the given auth_token.
-        :rtype: str
-        :raises ValueError: If no auth_token is provided for the model value.
-        """
-        if token is not None:
-            return token
-        else:
-            if self.model.value.startswith("gpt"):
-                token = os.environ.get("OPENAI_TOKEN")
-            elif self.model.value == "igel":
-                token = os.environ.get("IGEL_TOKEN")
-            if self.model.value.startswith("text-bison"):
-                token = os.environ.get("GOOGLE_TOKEN")
-
-        if token is None:
-            raise ValueError(f"No auth_token provided for model {self.model.value}.")
-        else:
-            return token
-
     def _estimate_tokens_openai(self, text: str) -> int:
         encoding = tiktoken.encoding_for_model(self.model.value)
         tokens = encoding.encode(text)