GPT-3.5 Turbo first brought ChatGPT-class conversational AI to the API at scale, delivering the same underlying capability at a price point that opened the door to production applications.
import { streamText } from 'ai'
const result = streamText({ model: 'openai/gpt-3.5-turbo', prompt: 'Why is the sky blue?'})GPT-3.5 Turbo launched on May 28, 2023 alongside the Whisper API as OpenAI opened its ChatGPT capability to developers through a dedicated API endpoint. At introduction it cost substantially less than the existing GPT-3.5 models, making it the first model to put conversational AI within budget for production-scale products.
The model uses a conversational message format where developers supply a list of messages with roles (system, user, assistant) rather than a single prompt string. This chat-native interface made it straightforward to build multi-turn experiences, chatbots, and instruction-following assistants without extra prompt engineering to simulate turns.
Over subsequent months OpenAI expanded the model: a 16K context variant arrived to handle roughly 20 pages of text in one request, and the standard model received a price reduction together with improved function-calling capabilities and better steerability. It remains widely deployed for workloads where conversational throughput and cost efficiency outweigh the need for frontier reasoning depth.