diff --git a/langchain/chat_models/openai.py b/langchain/chat_models/openai.py
index 83e43ae0ff1..f1725b83313 100644
--- a/langchain/chat_models/openai.py
+++ b/langchain/chat_models/openai.py
@@ -184,6 +184,16 @@ class ChatOpenAI(BaseChatModel):
     """Number of chat completions to generate for each prompt."""
     max_tokens: Optional[int] = None
     """Maximum number of tokens to generate."""
+    tiktoken_model_name: Optional[str] = None
+    """The model name to pass to tiktoken when using this class. 
+    Tiktoken is used to count the number of tokens in documents to constrain 
+    them to be under a certain limit. By default, when set to None, this will 
+    be the same as the embedding model name. However, there are some cases 
+    where you may want to use this Embedding class with a model name not 
+    supported by tiktoken. This can include when using Azure embeddings or 
+    when using one of the many model providers that expose an OpenAI-like 
+    API but with different models. In those cases, in order to avoid erroring 
+    when tiktoken is called, you can specify a model name to use here."""
 
     class Config:
         """Configuration for this pydantic object."""
@@ -448,15 +458,18 @@ class ChatOpenAI(BaseChatModel):
 
     def _get_encoding_model(self) -> Tuple[str, tiktoken.Encoding]:
         tiktoken_ = _import_tiktoken()
-        model = self.model_name
-        if model == "gpt-3.5-turbo":
-            # gpt-3.5-turbo may change over time.
-            # Returning num tokens assuming gpt-3.5-turbo-0301.
-            model = "gpt-3.5-turbo-0301"
-        elif model == "gpt-4":
-            # gpt-4 may change over time.
-            # Returning num tokens assuming gpt-4-0314.
-            model = "gpt-4-0314"
+        if self.tiktoken_model_name is not None:
+            model = self.tiktoken_model_name
+        else:
+            model = self.model_name
+            if model == "gpt-3.5-turbo":
+                # gpt-3.5-turbo may change over time.
+                # Returning num tokens assuming gpt-3.5-turbo-0301.
+                model = "gpt-3.5-turbo-0301"
+            elif model == "gpt-4":
+                # gpt-4 may change over time.
+                # Returning num tokens assuming gpt-4-0314.
+                model = "gpt-4-0314"
         # Returns the number of tokens used by a list of messages.
         try:
             encoding = tiktoken_.encoding_for_model(model)
diff --git a/langchain/embeddings/openai.py b/langchain/embeddings/openai.py
index 9c233230752..f3cb66547b7 100644
--- a/langchain/embeddings/openai.py
+++ b/langchain/embeddings/openai.py
@@ -170,6 +170,16 @@ class OpenAIEmbeddings(BaseModel, Embeddings):
     request_timeout: Optional[Union[float, Tuple[float, float]]] = None
     """Timeout in seconds for the OpenAPI request."""
     headers: Any = None
+    tiktoken_model_name: Optional[str] = None
+    """The model name to pass to tiktoken when using this class. 
+    Tiktoken is used to count the number of tokens in documents to constrain 
+    them to be under a certain limit. By default, when set to None, this will 
+    be the same as the embedding model name. However, there are some cases 
+    where you may want to use this Embedding class with a model name not 
+    supported by tiktoken. This can include when using Azure embeddings or 
+    when using one of the many model providers that expose an OpenAI-like 
+    API but with different models. In those cases, in order to avoid erroring 
+    when tiktoken is called, you can specify a model name to use here."""
 
     class Config:
         """Configuration for this pydantic object."""
@@ -265,7 +275,13 @@ class OpenAIEmbeddings(BaseModel, Embeddings):
 
         tokens = []
         indices = []
-        encoding = tiktoken.model.encoding_for_model(self.model)
+        model_name = self.tiktoken_model_name or self.model
+        try:
+            encoding = tiktoken.encoding_for_model(model_name)
+        except KeyError:
+            logger.warning("Warning: model not found. Using cl100k_base encoding.")
+            model = "cl100k_base"
+            encoding = tiktoken.get_encoding(model)
         for i, text in enumerate(texts):
             if self.model.endswith("001"):
                 # See: https://github.com/openai/openai-python/issues/418#issuecomment-1525939500
@@ -329,7 +345,13 @@ class OpenAIEmbeddings(BaseModel, Embeddings):
 
         tokens = []
         indices = []
-        encoding = tiktoken.model.encoding_for_model(self.model)
+        model_name = self.tiktoken_model_name or self.model
+        try:
+            encoding = tiktoken.encoding_for_model(model_name)
+        except KeyError:
+            logger.warning("Warning: model not found. Using cl100k_base encoding.")
+            model = "cl100k_base"
+            encoding = tiktoken.get_encoding(model)
         for i, text in enumerate(texts):
             if self.model.endswith("001"):
                 # See: https://github.com/openai/openai-python/issues/418#issuecomment-1525939500
diff --git a/langchain/llms/openai.py b/langchain/llms/openai.py
index 8fd350cbff5..19bce8bddcf 100644
--- a/langchain/llms/openai.py
+++ b/langchain/llms/openai.py
@@ -171,6 +171,16 @@ class BaseOpenAI(BaseLLM):
     """Set of special tokens that are allowed。"""
     disallowed_special: Union[Literal["all"], Collection[str]] = "all"
     """Set of special tokens that are not allowed。"""
+    tiktoken_model_name: Optional[str] = None
+    """The model name to pass to tiktoken when using this class. 
+    Tiktoken is used to count the number of tokens in documents to constrain 
+    them to be under a certain limit. By default, when set to None, this will 
+    be the same as the embedding model name. However, there are some cases 
+    where you may want to use this Embedding class with a model name not 
+    supported by tiktoken. This can include when using Azure embeddings or 
+    when using one of the many model providers that expose an OpenAI-like 
+    API but with different models. In those cases, in order to avoid erroring 
+    when tiktoken is called, you can specify a model name to use here."""
 
     def __new__(cls, **data: Any) -> Union[OpenAIChat, BaseOpenAI]:  # type: ignore
         """Initialize the OpenAI object."""
@@ -491,7 +501,13 @@ class BaseOpenAI(BaseLLM):
                 "Please install it with `pip install tiktoken`."
             )
 
-        enc = tiktoken.encoding_for_model(self.model_name)
+        model_name = self.tiktoken_model_name or self.model_name
+        try:
+            enc = tiktoken.encoding_for_model(model_name)
+        except KeyError:
+            logger.warning("Warning: model not found. Using cl100k_base encoding.")
+            model = "cl100k_base"
+            enc = tiktoken.get_encoding(model)
 
         return enc.encode(
             text,