diff --git a/Pipfile b/Pipfile
index 3d0e65e..c739635 100644
--- a/Pipfile
+++ b/Pipfile
@@ -24,6 +24,7 @@ libclang = "*"
 clang = "*"
 langchain = "*"
 langchain-openai = "*"
+langchain-community = "*"
 
 [dev-packages]
 pylint = "*"
diff --git a/esbmc_ai/__main__.py b/esbmc_ai/__main__.py
index f4ce4a9..8c528d3 100755
--- a/esbmc_ai/__main__.py
+++ b/esbmc_ai/__main__.py
@@ -218,7 +218,7 @@ def main() -> None:
         "-m",
         "--ai-model",
         default="",
-        help="Which AI model to use. Built-in models: {"
+        help="Which AI model to use. Built-in models: {OpenAI GPT models, "
         + ", ".join(_ai_model_names)
         + ", +custom models}",
     )
diff --git a/esbmc_ai/ai_models.py b/esbmc_ai/ai_models.py
index 1874bde..16120f7 100644
--- a/esbmc_ai/ai_models.py
+++ b/esbmc_ai/ai_models.py
@@ -1,7 +1,7 @@
 # Author: Yiannis Charalambous
 
 from abc import abstractmethod
-from typing import Any, Iterable, Union
+from typing import Any, Iterable, Optional, Union
 from enum import Enum
 from pydantic.v1.types import SecretStr
 from typing_extensions import override
@@ -152,6 +152,7 @@ def create_llm(
         requests_max_tries: int = 5,
         requests_timeout: float = 60,
     ) -> BaseLanguageModel:
+        assert api_keys.openai, "No OpenAI api key has been specified..."
         return ChatOpenAI(
             model=self.name,
             api_key=SecretStr(api_keys.openai),
@@ -267,11 +268,10 @@ def apply_chat_template(
         )
 
 
-class AIModels(Enum):
-    GPT_3 = AIModelOpenAI(name="gpt-3.5-turbo", tokens=4096)
-    GPT_3_16K = AIModelOpenAI(name="gpt-3.5-turbo-16k", tokens=16384)
-    GPT_4 = AIModelOpenAI(name="gpt-4", tokens=8192)
-    GPT_4_32K = AIModelOpenAI(name="gpt-4-32k", tokens=32768)
+class _AIModels(Enum):
+    """Private enum that contains predefined AI Models. OpenAI models are not
+    defined because they are fetched from the API."""
+
     FALCON_7B = AIModelTextGen(
         name="falcon-7b",
         tokens=8192,
@@ -295,7 +295,7 @@ class AIModels(Enum):
 
 _custom_ai_models: list[AIModel] = []
 
-_ai_model_names: set[str] = set(item.value.name for item in AIModels)
+_ai_model_names: set[str] = set(item.value.name for item in _AIModels)
 
 
 def add_custom_ai_model(ai_model: AIModel) -> None:
@@ -307,19 +307,82 @@ def add_custom_ai_model(ai_model: AIModel) -> None:
     _custom_ai_models.append(ai_model)
 
 
-def is_valid_ai_model(ai_model: Union[str, AIModel]) -> bool:
-    """Accepts both the AIModel object and the name as parameter."""
-    name: str
-    if isinstance(ai_model, AIModel):
-        name = ai_model.name
-    else:
-        name = ai_model
+def is_valid_ai_model(
+    ai_model: Union[str, AIModel], api_keys: Optional[APIKeyCollection] = None
+) -> bool:
+    """Accepts both the AIModel object and the name as parameter. It checks the
+    openai servers to see if a model is defined on their servers, if not, then
+    it checks the internally defined AI models list."""
+
+    # Get the name of the model
+    name: str = ai_model.name if isinstance(ai_model, AIModel) else ai_model
+
+    # Try accessing openai api and checking if there is a model defined.
+    # NOTE: This is not tested as no way to mock API currently.
+    if api_keys and api_keys.openai:
+        try:
+            from openai import Client
+
+            for model in Client(api_key=api_keys.openai).models.list().data:
+                if model.id == name:
+                    return True
+        except ImportError:
+            pass
+
+    # Use the predefined list of models.
     return name in _ai_model_names
 
 
-def get_ai_model_by_name(name: str) -> AIModel:
+def _get_openai_model_max_tokens(name: str) -> int:
+    """NOTE: OpenAI currently does not expose an API for getting the model
+    length. Maybe add a config input value for this?"""
+
+    # https://platform.openai.com/docs/models
+    tokens = {
+        "gpt-4o": 128000,
+        "gpt-4": 8192,
+        "gpt-3.5-turbo": 16385,
+        "gpt-3.5-turbo-instruct": 4096,
+    }
+
+    # Split into - segments and remove each section from the end to find out
+    # which one matches the most.
+
+    # Base Case
+    if name in tokens:
+        return tokens[name]
+
+    # Step Case
+    name_split: list[str] = name.split("-")
+    for i in range(1, name.count("-")):
+        subname: str = "-".join(name_split[:-i])
+        if subname in tokens:
+            return tokens[subname]
+
+    raise ValueError(f"Could not figure out max tokens for model: {name}")
+
+
+def get_ai_model_by_name(
+    name: str, api_keys: Optional[APIKeyCollection] = None
+) -> AIModel:
+    # Check OpenAI models.
+    if api_keys and api_keys.openai:
+        try:
+            from openai import Client
+
+            for model in Client(api_key=api_keys.openai).models.list().data:
+                if model.id == name:
+                    add_custom_ai_model(
+                        AIModelOpenAI(
+                            model.id,
+                            _get_openai_model_max_tokens(model.id),
+                        ),
+                    )
+        except ImportError:
+            pass
+
     # Check AIModels enum.
-    for enum_value in AIModels:
+    for enum_value in _AIModels:
         ai_model: AIModel = enum_value.value
         if name == ai_model.name:
             return ai_model
diff --git a/esbmc_ai/api_key_collection.py b/esbmc_ai/api_key_collection.py
index eba635d..9aeec6f 100644
--- a/esbmc_ai/api_key_collection.py
+++ b/esbmc_ai/api_key_collection.py
@@ -2,11 +2,11 @@
 
 """API Key Collection definition."""
 
-from typing import NamedTuple
+from typing import NamedTuple, Optional
 
 
 class APIKeyCollection(NamedTuple):
     """Class that is used to pass keys to AIModels."""
 
-    openai: str = ""
-    huggingface: str = ""
+    openai: Optional[str]
+    huggingface: Optional[str]
diff --git a/esbmc_ai/config.py b/esbmc_ai/config.py
index 3ce23fa..44007b3 100644
--- a/esbmc_ai/config.py
+++ b/esbmc_ai/config.py
@@ -38,7 +38,7 @@
 
 temp_auto_clean: bool = True
 temp_file_dir: str = "."
-ai_model: AIModel = AIModels.GPT_3.value
+ai_model: AIModel
 
 esbmc_output_type: str = "full"
 source_code_format: str = "full"
@@ -455,11 +455,10 @@ def load_config(file_path: str) -> None:
     ai_model_name, _ = _load_config_value(
         config_file,
         "ai_model",
-        ai_model,
     )
-    if is_valid_ai_model(ai_model_name):
+    if is_valid_ai_model(ai_model_name, api_keys):
         # Load the ai_model from loaded models.
-        ai_model = get_ai_model_by_name(ai_model_name)
+        ai_model = get_ai_model_by_name(ai_model_name, api_keys)
     else:
         print(f"Error: {ai_model_name} is not a valid AI model")
         sys.exit(4)
@@ -484,8 +483,8 @@ def load_args(args) -> None:
 
     global ai_model
     if args.ai_model != "":
-        if is_valid_ai_model(args.ai_model):
-            ai_model = get_ai_model_by_name(args.ai_model)
+        if is_valid_ai_model(args.ai_model, api_keys):
+            ai_model = get_ai_model_by_name(args.ai_model, api_keys)
         else:
             print(f"Error: invalid --ai-model parameter {args.ai_model}")
             sys.exit(4)
diff --git a/requirements.txt b/requirements.txt
index 41a599e..583ea95 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,153 +1,49 @@
 -i https://pypi.org/simple
-accelerate==0.20.3
-aiohttp==3.8.4
-aiosignal==1.3.1
-anthropic==0.2.10
-anyio==3.7.0 ; python_version >= '3.7'
-appdirs==1.4.4
-asgiref==3.7.2 ; python_version >= '3.7'
-async-timeout==4.0.2
-attrs==23.1.0
-bentoml[grpc,io]==1.0.22 ; python_version >= '3.7'
-build==0.10.0 ; python_version >= '3.7'
-cattrs==23.1.2 ; python_version >= '3.7'
-certifi==2022.12.7
-charset-normalizer==3.1.0
-circus==0.18.0 ; python_version >= '3.7'
-clang==16.0.1.1
-clarifai==9.1.0
-clarifai-grpc==9.5.0 ; python_version >= '3.8'
-click==8.1.3 ; python_version >= '3.7'
-click-option-group==0.5.6 ; python_version >= '3.6' and python_version < '4'
-cloudpickle==2.2.1 ; python_version >= '3.6'
-cmake==3.26.4
-cohere==3.10.0
-coloredlogs==15.0.1 ; python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3, 3.4'
-contextlib2==21.6.0 ; python_version >= '3.6'
-dataclasses-json==0.5.8 ; python_version >= '3.6'
-datasets==2.13.0 ; python_full_version >= '3.7.0'
-deepmerge==1.1.0
-deprecated==1.2.14 ; python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'
-dill==0.3.6 ; python_version >= '3.7'
-filelock==3.12.2 ; python_version >= '3.7'
-filetype==1.2.0
-frozenlist==1.3.3
-fs==2.4.16
-fsspec==2023.6.0 ; python_version >= '3.8'
-googleapis-common-protos==1.59.1 ; python_version >= '3.7'
-greenlet==2.0.2 ; platform_machine == 'aarch64' or (platform_machine == 'ppc64le' or (platform_machine == 'x86_64' or (platform_machine == 'amd64' or (platform_machine == 'AMD64' or (platform_machine == 'win32' or platform_machine == 'WIN32')))))
-grpcio==1.54.2
-grpcio-health-checking==1.48.2
-h11==0.14.0 ; python_version >= '3.7'
-httpcore==0.17.2 ; python_version >= '3.7'
-httpx==0.24.1 ; python_version >= '3.7'
-huggingface-hub==0.15.1 ; python_full_version >= '3.7.0'
-humanfriendly==10.0 ; python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3, 3.4'
-idna==3.4
-importlib-metadata==6.0.1 ; python_version >= '3.7'
-inflection==0.5.1 ; python_version >= '3.5'
-jinja2==3.1.2 ; python_version >= '3.7'
-langchain[llms]==0.0.209
-langchainplus-sdk==0.0.16 ; python_version < '4.0' and python_full_version >= '3.8.1'
-libclang==16.0.0
-lit==16.0.6
-manifest-ml==0.0.1
-markdown-it-py==3.0.0 ; python_version >= '3.8'
-markupsafe==2.1.3 ; python_version >= '3.7'
-marshmallow==3.19.0 ; python_version >= '3.7'
-marshmallow-enum==1.5.1
-mdurl==0.1.2 ; python_version >= '3.7'
-mpmath==1.3.0
-multidict==6.0.4
-multiprocess==0.70.14 ; python_version >= '3.7'
-mypy-extensions==1.0.0 ; python_version >= '3.5'
-networkx==3.1 ; python_version >= '3.8'
-nlpcloud==1.0.42
-numexpr==2.8.4 ; python_version >= '3.7'
-numpy==1.25.0 ; python_version >= '3.9'
-nvidia-cublas-cu11==11.10.3.66 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-nvidia-cuda-cupti-cu11==11.7.101 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-nvidia-cuda-nvrtc-cu11==11.7.99 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-nvidia-cuda-runtime-cu11==11.7.99 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-nvidia-cudnn-cu11==8.5.0.96 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-nvidia-cufft-cu11==10.9.0.58 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-nvidia-curand-cu11==10.2.10.91 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-nvidia-cusolver-cu11==11.4.0.1 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-nvidia-cusparse-cu11==11.7.4.91 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-nvidia-nccl-cu11==2.14.3 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-nvidia-nvtx-cu11==11.7.91 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-openai==0.27.5
-openapi-schema-pydantic==1.2.4 ; python_full_version >= '3.6.1'
-openllm==0.1.10
-openlm==0.0.5
-opentelemetry-api==1.17.0 ; python_version >= '3.7'
-opentelemetry-instrumentation==0.38b0 ; python_version >= '3.7'
-opentelemetry-instrumentation-aiohttp-client==0.38b0 ; python_version >= '3.7'
-opentelemetry-instrumentation-asgi==0.38b0 ; python_version >= '3.7'
-opentelemetry-instrumentation-grpc==0.38b0
-opentelemetry-sdk==1.17.0 ; python_version >= '3.7'
-opentelemetry-semantic-conventions==0.38b0 ; python_version >= '3.7'
-opentelemetry-util-http==0.38b0 ; python_version >= '3.7'
-optimum==1.8.8 ; python_full_version >= '3.7.0'
-orjson==3.9.1 ; python_version >= '3.7'
-packaging==23.1 ; python_version >= '3.7'
-pandas==2.0.2
-pathspec==0.11.1 ; python_version >= '3.7'
-pillow==9.5.0
-pip==23.1.2 ; python_version >= '3.7'
-pip-requirements-parser==32.0.1 ; python_full_version >= '3.6.0'
-pip-tools==6.13.0 ; python_version >= '3.7'
-prometheus-client==0.17.0 ; python_version >= '3.6'
-protobuf==3.20.3
-psutil==5.9.5 ; python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'
-pyarrow==12.0.1
-pydantic==1.10.9 ; python_version >= '3.7'
-pygments==2.15.1 ; python_version >= '3.7'
-pynvml==11.5.0 ; python_version >= '3.6'
-pyparsing==3.1.0 ; python_full_version >= '3.6.8'
-pyproject-hooks==1.0.0 ; python_version >= '3.7'
-python-dateutil==2.8.2 ; python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'
-python-dotenv==1.0.0
-python-json-logger==2.0.7 ; python_version >= '3.6'
-python-multipart==0.0.6 ; python_version >= '3.7'
-pytz==2023.3
-pyyaml==6.0 ; python_version >= '3.6'
-pyzmq==25.1.0 ; python_version >= '3.6'
-redis==4.5.5 ; python_version >= '3.7'
-regex==2023.3.23
-requests==2.29.0
-rich==13.4.2 ; python_full_version >= '3.7.0'
-safetensors==0.3.1
-schema==0.7.5
-sentencepiece==0.1.99
-setuptools==68.0.0 ; python_version >= '3.7'
-simple-di==0.1.5 ; python_full_version >= '3.6.1'
-six==1.16.0 ; python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'
-sniffio==1.3.0 ; python_version >= '3.7'
-sqlalchemy==2.0.16 ; python_version >= '3.7'
-sqlitedict==2.1.0
-starlette==0.28.0 ; python_version >= '3.7'
-sympy==1.12 ; python_version >= '3.8'
-tabulate[widechars]==0.9.0 ; python_version >= '3.7'
-tenacity==8.2.2 ; python_version >= '3.6'
-text-generation==0.6.0
-tiktoken==0.3.3
-tokenizers==0.13.3
-torch==2.0.1
-torchvision==0.15.2 ; python_version >= '3.8'
-tornado==6.3.2 ; python_version >= '3.8'
-tqdm==4.65.0
-transformers==4.30.2
-triton==2.0.0 ; platform_system == 'Linux' and platform_machine == 'x86_64'
-typing-extensions==4.6.3 ; python_version >= '3.7'
+aiohttp==3.8.4; python_version >= '3.6'
+aiosignal==1.3.1; python_version >= '3.7'
+annotated-types==0.6.0; python_version >= '3.8'
+anyio==4.3.0; python_version >= '3.8'
+async-timeout==4.0.2; python_version >= '3.6'
+attrs==23.1.0; python_version >= '3.7'
+certifi==2022.12.7; python_version >= '3.6'
+charset-normalizer==3.1.0; python_full_version >= '3.7.0'
+clang==17.0.6
+dataclasses-json==0.6.4; python_version >= '3.7' and python_version < '4.0'
+distro==1.9.0; python_version >= '3.6'
+frozenlist==1.3.3; python_version >= '3.7'
+greenlet==3.0.3; platform_machine == 'aarch64' or (platform_machine == 'ppc64le' or (platform_machine == 'x86_64' or (platform_machine == 'amd64' or (platform_machine == 'AMD64' or (platform_machine == 'win32' or platform_machine == 'WIN32')))))
+h11==0.14.0; python_version >= '3.7'
+httpcore==1.0.5; python_version >= '3.8'
+httpx==0.27.0; python_version >= '3.8'
+idna==3.4; python_version >= '3.5'
+jsonpatch==1.33; python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6'
+jsonpointer==2.4; python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6'
+langchain==0.1.16; python_version < '4.0' and python_full_version >= '3.8.1'
+langchain-community==0.0.34; python_version < '4.0' and python_full_version >= '3.8.1'
+langchain-core==0.1.45; python_version < '4.0' and python_full_version >= '3.8.1'
+langchain-openai==0.1.3; python_version < '4.0' and python_full_version >= '3.8.1'
+langchain-text-splitters==0.0.1; python_version < '4.0' and python_full_version >= '3.8.1'
+langsmith==0.1.49; python_version < '4.0' and python_full_version >= '3.8.1'
+libclang==18.1.1
+marshmallow==3.21.1; python_version >= '3.8'
+multidict==6.0.4; python_version >= '3.7'
+mypy-extensions==1.0.0; python_version >= '3.5'
+numpy==1.26.4; python_version >= '3.9'
+openai==1.23.2; python_full_version >= '3.7.1'
+orjson==3.10.1; python_version >= '3.8'
+packaging==23.2; python_version >= '3.7'
+pydantic==2.7.0; python_version >= '3.8'
+pydantic-core==2.18.1; python_version >= '3.8'
+python-dotenv==1.0.0; python_version >= '3.8'
+pyyaml==6.0.1; python_version >= '3.6'
+regex==2023.3.23; python_version >= '3.8'
+requests==2.29.0; python_version >= '3.7'
+sniffio==1.3.1; python_version >= '3.7'
+sqlalchemy==2.0.29; python_version >= '3.7'
+tenacity==8.2.3; python_version >= '3.7'
+tiktoken==0.6.0; python_version >= '3.8'
+tqdm==4.66.2; python_version >= '3.7'
+typing-extensions==4.11.0; python_version >= '3.8'
 typing-inspect==0.9.0
-tzdata==2023.3 ; python_version >= '2'
-urllib3==1.26.15
-uvicorn==0.22.0 ; python_version >= '3.7'
-watchfiles==0.19.0 ; python_version >= '3.7'
-wcwidth==0.2.6
-wheel==0.40.0 ; python_version >= '3.7'
-wrapt==1.15.0 ; python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3, 3.4'
-xxhash==3.2.0 ; python_version >= '3.6'
-yarl==1.9.2
-zipp==3.15.0 ; python_version >= '3.7'
+urllib3==1.26.15; python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3, 3.4, 3.5'
+yarl==1.9.2; python_version >= '3.7'
diff --git a/tests/test_ai_models.py b/tests/test_ai_models.py
index e9bdba6..028bff3 100644
--- a/tests/test_ai_models.py
+++ b/tests/test_ai_models.py
@@ -13,16 +13,18 @@
     add_custom_ai_model,
     is_valid_ai_model,
     AIModel,
-    AIModels,
+    _AIModels,
     get_ai_model_by_name,
     AIModelTextGen,
+    _get_openai_model_max_tokens,
 )
 
+"""TODO Find a way to mock the OpenAI API and test GPT LLM code."""
+
 
 def test_is_valid_ai_model() -> None:
-    assert is_valid_ai_model(AIModels.FALCON_7B.value)
-    assert is_valid_ai_model(AIModels.GPT_3_16K.value)
-    assert is_valid_ai_model("gpt-3.5-turbo")
+    assert is_valid_ai_model(_AIModels.FALCON_7B.value)
+    assert is_valid_ai_model(_AIModels.STARCHAT_BETA.value)
     assert is_valid_ai_model("falcon-7b")
 
 
@@ -56,7 +58,7 @@ def test_add_custom_ai_model() -> None:
 
 def test_get_ai_model_by_name() -> None:
     # Try with first class AI
-    assert get_ai_model_by_name("gpt-3.5-turbo")
+    assert get_ai_model_by_name("falcon-7b")
 
     # Try with custom AI.
     # Add custom AI model if not added by previous tests.
@@ -141,3 +143,15 @@ def test_escape_messages() -> None:
     assert result[3] == filtered[3]
     assert result[4] == filtered[4]
     assert result[5] == filtered[5]
+
+
+def test__get_openai_model_max_tokens() -> None:
+    assert _get_openai_model_max_tokens("gpt-4o") == 128000
+    assert _get_openai_model_max_tokens("gpt-4-turbo") == 8192
+    assert _get_openai_model_max_tokens("gpt-3.5-turbo") == 16385
+    assert _get_openai_model_max_tokens("gpt-3.5-turbo-instruct") == 4096
+    assert _get_openai_model_max_tokens("gpt-3.5-turbo-aaaaaa") == 16385
+    assert _get_openai_model_max_tokens("gpt-3.5-turbo-instruct-bbb") == 4096
+
+    with raises(ValueError):
+        _get_openai_model_max_tokens("aaaaa")