diff --git a/pageindex/page_index.py b/pageindex/page_index.py
index 39018c4df..8237f1123 100644
--- a/pageindex/page_index.py
+++ b/pageindex/page_index.py
@@ -36,7 +36,7 @@ async def check_title_appearance(item, page_list, start_index=1, model=None):
     }}
     Directly return the final JSON structure. Do not output anything else."""
 
-    response = await ChatGPT_API_async(model=model, prompt=prompt)
+    response = await OpenAI_API_async(model=model, prompt=prompt)
     response = extract_json(response)
     if 'answer' in response:
         answer = response['answer']
@@ -64,7 +64,7 @@ async def check_title_appearance_in_start(title, page_text, model=None, logger=N
     }}
     Directly return the final JSON structure. Do not output anything else."""
 
-    response = await ChatGPT_API_async(model=model, prompt=prompt)
+    response = await OpenAI_API_async(model=model, prompt=prompt)
     response = extract_json(response)
     if logger:
         logger.info(f"Response: {response}")
@@ -116,7 +116,7 @@ def toc_detector_single_page(content, model=None):
     Directly return the final JSON structure. Do not output anything else.
     Please note: abstract,summary, notation list, figure list, table list, etc. are not table of contents."""
 
-    response = ChatGPT_API(model=model, prompt=prompt)
+    response = OpenAI_API(model=model, prompt=prompt)
     # print('response', response)
     json_content = extract_json(response)    
     return json_content['toc_detected']
@@ -135,7 +135,7 @@ def check_if_toc_extraction_is_complete(content, toc, model=None):
     Directly return the final JSON structure. Do not output anything else."""
 
     prompt = prompt + '\n Document:\n' + content + '\n Table of contents:\n' + toc
-    response = ChatGPT_API(model=model, prompt=prompt)
+    response = OpenAI_API(model=model, prompt=prompt)
     json_content = extract_json(response)
     return json_content['completed']
 
@@ -153,7 +153,7 @@ def check_if_toc_transformation_is_complete(content, toc, model=None):
     Directly return the final JSON structure. Do not output anything else."""
 
     prompt = prompt + '\n Raw Table of contents:\n' + content + '\n Cleaned Table of contents:\n' + toc
-    response = ChatGPT_API(model=model, prompt=prompt)
+    response = OpenAI_API(model=model, prompt=prompt)
     json_content = extract_json(response)
     return json_content['completed']
 
@@ -165,7 +165,7 @@ def extract_toc_content(content, model=None):
 
     Directly return the full table of contents content. Do not output anything else."""
 
-    response, finish_reason = ChatGPT_API_with_finish_reason(model=model, prompt=prompt)
+    response, finish_reason = OpenAI_API_with_finish_reason(model=model, prompt=prompt)
     
     if_complete = check_if_toc_transformation_is_complete(content, response, model)
     if if_complete == "yes" and finish_reason == "finished":
@@ -176,7 +176,7 @@ def extract_toc_content(content, model=None):
         {"role": "assistant", "content": response},    
     ]
     prompt = f"""please continue the generation of table of contents , directly output the remaining part of the structure"""
-    new_response, finish_reason = ChatGPT_API_with_finish_reason(model=model, prompt=prompt, chat_history=chat_history)
+    new_response, finish_reason = OpenAI_API_with_finish_reason(model=model, prompt=prompt, chat_history=chat_history)
     response = response + new_response
     if_complete = check_if_toc_transformation_is_complete(content, response, model)
     
@@ -186,7 +186,7 @@ def extract_toc_content(content, model=None):
             {"role": "assistant", "content": response},    
         ]
         prompt = f"""please continue the generation of table of contents , directly output the remaining part of the structure"""
-        new_response, finish_reason = ChatGPT_API_with_finish_reason(model=model, prompt=prompt, chat_history=chat_history)
+        new_response, finish_reason = OpenAI_API_with_finish_reason(model=model, prompt=prompt, chat_history=chat_history)
         response = response + new_response
         if_complete = check_if_toc_transformation_is_complete(content, response, model)
         
@@ -212,7 +212,7 @@ def detect_page_index(toc_content, model=None):
     }}
     Directly return the final JSON structure. Do not output anything else."""
 
-    response = ChatGPT_API(model=model, prompt=prompt)
+    response = OpenAI_API(model=model, prompt=prompt)
     json_content = extract_json(response)
     return json_content['page_index_given_in_toc']
 
@@ -261,7 +261,7 @@ def toc_index_extractor(toc, content, model=None):
     Directly return the final JSON structure. Do not output anything else."""
 
     prompt = toc_extractor_prompt + '\nTable of contents:\n' + str(toc) + '\nDocument pages:\n' + content
-    response = ChatGPT_API(model=model, prompt=prompt)
+    response = OpenAI_API(model=model, prompt=prompt)
     json_content = extract_json(response)    
     return json_content
 
@@ -289,7 +289,7 @@ def toc_transformer(toc_content, model=None):
     Directly return the final JSON structure, do not output anything else. """
 
     prompt = init_prompt + '\n Given table of contents\n:' + toc_content
-    last_complete, finish_reason = ChatGPT_API_with_finish_reason(model=model, prompt=prompt)
+    last_complete, finish_reason = OpenAI_API_with_finish_reason(model=model, prompt=prompt)
     if_complete = check_if_toc_transformation_is_complete(toc_content, last_complete, model)
     if if_complete == "yes" and finish_reason == "finished":
         last_complete = extract_json(last_complete)
@@ -313,7 +313,7 @@ def toc_transformer(toc_content, model=None):
 
         Please continue the json structure, directly output the remaining part of the json structure."""
 
-        new_complete, finish_reason = ChatGPT_API_with_finish_reason(model=model, prompt=prompt)
+        new_complete, finish_reason = OpenAI_API_with_finish_reason(model=model, prompt=prompt)
 
         if new_complete.startswith('```json'):
             new_complete =  get_json_content(new_complete)
@@ -474,7 +474,7 @@ def add_page_number_to_toc(part, structure, model=None):
     Directly return the final JSON structure. Do not output anything else."""
 
     prompt = fill_prompt_seq + f"\n\nCurrent Partial Document:\n{part}\n\nGiven Structure\n{json.dumps(structure, indent=2)}\n"
-    current_json_raw = ChatGPT_API(model=model, prompt=prompt)
+    current_json_raw = OpenAI_API(model=model, prompt=prompt)
     json_result = extract_json(current_json_raw)
     
     for item in json_result:
@@ -524,7 +524,7 @@ def generate_toc_continue(toc_content, part, model="gpt-4o-2024-11-20"):
     Directly return the additional part of the final JSON structure. Do not output anything else."""
 
     prompt = prompt + '\nGiven text\n:' + part + '\nPrevious tree structure\n:' + json.dumps(toc_content, indent=2)
-    response, finish_reason = ChatGPT_API_with_finish_reason(model=model, prompt=prompt)
+    response, finish_reason = OpenAI_API_with_finish_reason(model=model, prompt=prompt)
     if finish_reason == 'finished':
         return extract_json(response)
     else:
@@ -558,7 +558,7 @@ def generate_toc_init(part, model=None):
     Directly return the final JSON structure. Do not output anything else."""
 
     prompt = prompt + '\nGiven text\n:' + part
-    response, finish_reason = ChatGPT_API_with_finish_reason(model=model, prompt=prompt)
+    response, finish_reason = OpenAI_API_with_finish_reason(model=model, prompt=prompt)
 
     if finish_reason == 'finished':
          return extract_json(response)
@@ -743,7 +743,7 @@ def single_toc_item_index_fixer(section_title, content, model="gpt-4o-2024-11-20
     Directly return the final JSON structure. Do not output anything else."""
 
     prompt = toc_extractor_prompt + '\nSection Title:\n' + str(section_title) + '\nDocument pages:\n' + content
-    response = ChatGPT_API(model=model, prompt=prompt)
+    response = OpenAI_API(model=model, prompt=prompt)
     json_content = extract_json(response)    
     return convert_physical_index_to_int(json_content['physical_index'])
 
@@ -1141,4 +1141,4 @@ def validate_and_truncate_physical_indices(toc_with_page_number, page_list_lengt
     if truncated_items:
         print(f"Truncated {len(truncated_items)} TOC items that exceeded document length")
      
-    return toc_with_page_number
\ No newline at end of file
+    return toc_with_page_number
diff --git a/pageindex/page_index_md.py b/pageindex/page_index_md.py
index 70e8de086..331b7ff1c 100644
--- a/pageindex/page_index_md.py
+++ b/pageindex/page_index_md.py
@@ -300,13 +300,15 @@ async def md_to_tree(md_path, if_thinning=False, min_token_threshold=None, if_ad
 if __name__ == "__main__":
     import os
     import json
+    from dotenv import load_dotenv
+    load_dotenv()
     
     # MD_NAME = 'Detect-Order-Construct'
     MD_NAME = 'cognitive-load'
     MD_PATH = os.path.join(os.path.dirname(__file__), '..', 'tests/markdowns/', f'{MD_NAME}.md')
 
 
-    MODEL="gpt-4.1"
+    MODEL = os.getenv('OPENAI_MODEL', 'gpt-4.1')
     IF_THINNING=False
     THINNING_THRESHOLD=5000
     SUMMARY_TOKEN_THRESHOLD=200
@@ -336,4 +338,4 @@ async def md_to_tree(md_path, if_thinning=False, min_token_threshold=None, if_ad
     with open(output_path, 'w', encoding='utf-8') as f:
         json.dump(tree_structure, f, indent=2, ensure_ascii=False)
     
-    print(f"\nTree structure saved to: {output_path}")
\ No newline at end of file
+    print(f"\nTree structure saved to: {output_path}")
diff --git a/pageindex/utils.py b/pageindex/utils.py
index dc7acd888..6fa408157 100644
--- a/pageindex/utils.py
+++ b/pageindex/utils.py
@@ -17,7 +17,9 @@
 from pathlib import Path
 from types import SimpleNamespace as config
 
-CHATGPT_API_KEY = os.getenv("CHATGPT_API_KEY")
+OPENAI_API_KEY = os.getenv("OPENAI_API_KEY")
+OPENAI_MODEL = os.getenv("OPENAI_MODEL", "gpt-4o-2024-11-20")
+OPENAI_BASE_URL = os.getenv("OPENAI_BASE_URL", "https://api.openai.com/v1")
 
 def count_tokens(text, model=None):
     if not text:
@@ -26,9 +28,9 @@ def count_tokens(text, model=None):
     tokens = enc.encode(text)
     return len(tokens)
 
-def ChatGPT_API_with_finish_reason(model, prompt, api_key=CHATGPT_API_KEY, chat_history=None):
+def OpenAI_API_with_finish_reason(model, prompt, api_key=OPENAI_API_KEY, chat_history=None):
     max_retries = 10
-    client = openai.OpenAI(api_key=api_key)
+    client = openai.OpenAI(api_key=api_key, base_url=OPENAI_BASE_URL)
     for i in range(max_retries):
         try:
             if chat_history:
@@ -58,9 +60,9 @@ def ChatGPT_API_with_finish_reason(model, prompt, api_key=CHATGPT_API_KEY, chat_
 
 
 
-def ChatGPT_API(model, prompt, api_key=CHATGPT_API_KEY, chat_history=None):
+def OpenAI_API(model, prompt, api_key=OPENAI_API_KEY, chat_history=None):
     max_retries = 10
-    client = openai.OpenAI(api_key=api_key)
+    client = openai.OpenAI(api_key=api_key, base_url=OPENAI_BASE_URL)
     for i in range(max_retries):
         try:
             if chat_history:
@@ -86,12 +88,12 @@ def ChatGPT_API(model, prompt, api_key=CHATGPT_API_KEY, chat_history=None):
                 return "Error"
             
 
-async def ChatGPT_API_async(model, prompt, api_key=CHATGPT_API_KEY):
+async def OpenAI_API_async(model, prompt, api_key=OPENAI_API_KEY):
     max_retries = 10
     messages = [{"role": "user", "content": prompt}]
     for i in range(max_retries):
         try:
-            async with openai.AsyncOpenAI(api_key=api_key) as client:
+            async with openai.AsyncOpenAI(api_key=api_key, base_url=OPENAI_BASE_URL) as client:
                 response = await client.chat.completions.create(
                     model=model,
                     messages=messages,
@@ -609,7 +611,7 @@ async def generate_node_summary(node, model=None):
     
     Directly return the description, do not include any other text.
     """
-    response = await ChatGPT_API_async(model, prompt)
+    response = await OpenAI_API_async(model, prompt)
     return response
 
 
@@ -654,7 +656,7 @@ def generate_doc_description(structure, model=None):
     
     Directly return the description, do not include any other text.
     """
-    response = ChatGPT_API(model, prompt)
+    response = OpenAI_API(model, prompt)
     return response
 
 
@@ -709,4 +711,4 @@ def load(self, user_opt=None) -> config:
 
         self._validate_keys(user_dict)
         merged = {**self._default_dict, **user_dict}
-        return config(**merged)
\ No newline at end of file
+        return config(**merged)
diff --git a/run_pageindex.py b/run_pageindex.py
index 107024505..2de8a0b5c 100644
--- a/run_pageindex.py
+++ b/run_pageindex.py
@@ -3,6 +3,8 @@
 import json
 from pageindex import *
 from pageindex.page_index_md import md_to_tree
+from dotenv import load_dotenv
+load_dotenv()
 
 if __name__ == "__main__":
     # Set up argument parser
@@ -10,7 +12,7 @@
     parser.add_argument('--pdf_path', type=str, help='Path to the PDF file')
     parser.add_argument('--md_path', type=str, help='Path to the Markdown file')
 
-    parser.add_argument('--model', type=str, default='gpt-4o-2024-11-20', help='Model to use')
+    parser.add_argument('--model', type=str, default=os.getenv('OPENAI_MODEL', 'gpt-4o-2024-11-20'), help='Model to use')
 
     parser.add_argument('--toc-check-pages', type=int, default=20, 
                       help='Number of pages to check for table of contents (PDF only)')
@@ -130,4 +132,4 @@
         with open(output_file, 'w', encoding='utf-8') as f:
             json.dump(toc_with_page_number, f, indent=2, ensure_ascii=False)
         
-        print(f'Tree structure saved to: {output_file}')
\ No newline at end of file
+        print(f'Tree structure saved to: {output_file}')