GPT-3.5
5 is a large language model developed by OpenAI, released in 2022 as an improvement over GPT-3 and best known as the original model powering the free tier of ChatGPT at its November 2022 launch.
Definition
GPT-3.5 is a large language model developed by OpenAI, released in 2022 as an improvement over GPT-3 and best known as the original model powering the free tier of ChatGPT at its November 2022 launch.
Overview
GPT-3.5 refers to a family of models OpenAI released as an evolution of GPT-3, incorporating techniques such as instruction tuning and reinforcement learning from human feedback (RLHF) to make the model follow instructions more reliably and produce more helpful, conversational responses. The most consequential release in this family was gpt-3.5-turbo, which powered the free version of ChatGPT when it launched on November 30, 2022 — the product that is widely credited with triggering the mainstream generative AI boom. Compared to base GPT-3, GPT-3.5 models were significantly better at following natural-language instructions, holding multi-turn conversations, and refusing clearly inappropriate requests, largely due to RLHF fine-tuning pioneered in OpenAI's InstructGPT work. GPT-3.5 was made available via the OpenAI API at a much lower price point than GPT-4, making it attractive for high-volume applications such as chatbots, summarization tools, and content generation pipelines where GPT-4-level reasoning wasn't required. GPT-3.5 was eventually surpassed by GPT-4 in March 2023 for tasks requiring stronger reasoning, and OpenAI continued to offer gpt-3.5-turbo as a fast, economical option in the API for years afterward. As OpenAI's model lineup evolved through GPT-4o, GPT-4.1, and the GPT-5 series, GPT-3.5 was gradually phased out of ChatGPT's default offerings and deprecated in the API, though it remains historically significant as the model that first demonstrated to a mass consumer audience what a capable, instruction-following chatbot could do.
Key Features
- Instruction-tuned successor to GPT-3, trained with RLHF
- Powered the free tier of ChatGPT at its November 2022 launch
- Offered via the OpenAI API as gpt-3.5-turbo at low cost relative to GPT-4
- Strong at conversational, multi-turn dialogue and instruction following
- Smaller and faster than GPT-4, with correspondingly lower reasoning capability
- Widely fine-tuned by developers for custom chatbot and text-generation applications