https://arstechnica.com/information-technology/2023/06/openai-rolls-out-big-chatbot-api-upgrades-for-developers/

On Tuesday, OpenAI announced a sizable update to its large language model API offerings (including GPT-4 and gpt-3.5-turbo), including a new function calling capability, significant cost reductions, and a 16,000 token context window option for the gpt-3.5-turbo model.