How can I retrieve the maximum token limit for an OpenAI model via the API?

Below is an explanation of the current situation and some best practices:

Current Situation

At the moment, the OpenAPI models endpoint does not expose a property (such as "max_tokens" or "context_length") that tells you the maximum token limit for a given model. As you’ve discovered with your query for gpt-3.5-turbo, you only end up finding out the limit when you trigger an error by exceeding it. The error message you received:

JSONCopied
{
  "message": "This model's maximum context length is 4097 tokens. However, your messages resulted in 5975 tokens. Please reduce the length of the messages."
}

reveals the effective limit, but only after the submission.

Why This Matters

Having the max token limit available via the API would allow you to validate user input before sending it to OpenAI, helping avoid unnecessary errors or rejections. Relying on hard-coded limits or documentation alone can lead to discrepancies (as seen between 4096 and 4097 tokens) or issues when OpenAI updates these values.

Best Practices and Tips

1. Mapping Based on Documentation:
   Until an API endpoint is provided, you might maintain an internal mapping (or configuration file) of models to their token limits. For example:

   JSONCopied
   {
     "gpt-3.5-turbo": 4097,
     "gpt-4": 8192  // example value, adjust as per official docs
   }

2. Token Counting Libraries:
   Use libraries like tiktoken to tokenize your user input. This lets you accurately count the number of tokens before submission:

   PYTHONCopied
   import tiktoken
   
   # Example with a hypothetical encoding
   encoding = tiktoken.encoding_for_model("gpt-3.5-turbo")
   tokens = encoding.encode(user_input)
   if len(tokens) > 4097:
       raise ValueError("Input too long for gpt-3.5-turbo")

3. Error Handling:
   Even with pre-checks, always include robust error handling so that if the token limit is exceeded, the application can handle the error gracefully.

Looking Ahead

It would indeed be a beneficial feature if OpenAI provided an API method to query a model’s token limits directly. This would remove the need for hard-coded values and reduce the chance of unexpected behavior. For now, staying updated with the official documentation and using community tools remains the best approach.

If further improvements are made or an endpoint to retrieve these details is added in the future, migrating to that solution would be recommended.