GPT3.5 models:
                           max tokens         $/1K tokens
[0] gpt-3.5-turbo ........ 4,096 ............ 0.002
[1] gpt-3.5-turbo-16k .... 16,384 ........... 0.004


GPT4 models:
                           max tokens         $/1000 tokens
[2] gpt-4 ................ 8,192 ............ 0.06
[3] gpt-4-32k ............ 32,768 ........... 0.12
