GPT-4.5 explained: Everything you need to know

What is GPT-4.5?

At the time of its initial research preview release on Feb. 27, 2025, it was the most advanced GPT class model in OpenAI's portfolio, exceeding the capabilities of models including GPT-4o, GPT-4 and prior models. Like its predecessors, GPT-4.5 is a transformer model-based LLM.

The acronym GPT itself stands for generative pre-trained transformer. A transformer model is a key component of generative AI, offering a neural network architecture capable of comprehending and generating new outputs.

While previous iterations, such as GPT-4o, emphasized multimodal capabilities, the GPT-4.5 model prioritizes nuanced understanding and improved natural interactions. Alongside the more fluid interactions, OpenAI developed GPT-4.5 to have fewer inaccuracies -- known as hallucinations -- than its prior GPT class models.

GPT-4.5 focuses on advancing unsupervised learning rather than chain-of-thought reasoning. Unlike reasoning-focused models such as o3 and DeepSeek R1, which use chain-of-thought processing to reason through complex problems methodically, GPT-4.5 responds based on its training data and pattern recognition capabilities. GPT-4.5 has a more general purpose than specialized reasoning models that excel at complex math, science and logic problems.

OpenAI did not disclose the precise size or parameter count for GPT-4.5 at launch, but the company claimed it was the largest model it had ever built at the time. GPT-4.5 incorporates extensive pretraining on diverse data sets, including publicly available sources, proprietary partnerships and custom data developed internally.

How GPT-4.5 was trained

OpenAI used a series of techniques in developing and training GPT-4.5. Built upon GPT-4o's foundation, it features expanded pretraining and other novel approaches to improve performance and reduce the risk of hallucinations.

Training techniques used in GPT-4.5 include the following:

• Supervised fine-tuning. This process aligned GPT-4.5 with human expectations and taught it to follow instructions effectively. OpenAI implemented advanced data filtering during this phase to minimize exposure to potentially harmful content.
• Reinforcement learning from human feedback (RLHF). OpenAI refined GPT-4.5 through RLHF, where human evaluators ranked model outputs based on quality, helpfulness and safety.
• Instruction hierarchy training. GPT-4.5 was trained to follow an instruction hierarchy that prioritizes system messages over conflicting user instructions to prevent prompt injection.

What can GPT-4.5 do?

OpenAI's GPT-4.5 offers many advanced capabilities that improve upon previous models.

Capabilities of GPT-4.5 include the following:

• Natural conversation. Natural language processing has always been part of the GPT series models. However, interaction with GPT-4.5 is intended to be more natural, with an improved understanding of conversation nuance.
• Emotional intelligence. GPT-4.5 integrates a deep level of sentiment analysis with the ability to understand when to offer advice or simply listen when handling emotionally charged queries.
• Content generation. The GPT-4.5 model can generate various forms of text content for users, including creative writing.
• Content summarization. The model can summarize large documents and volumes of content in clear and succinct summaries that provide more detail than prior models.
• Knowledge-based Q&A. GPT-4.5 features a broader knowledge base for answering queries.
• File and image uploads. GPT-4.5 supports file and image uploads, enabling additional data to be analyzed.
• Multilingual proficiency. The model performs well across 14 languages, outperforming GPT-4o in multilingual benchmarks, including Arabic, Bengali, Chinese, French, German, Hindi, Italian, Japanese, Korean, Spanish and Swahili.
• Programming assistance. GPT-4.5 can act as a coding assistant, helping build software applications.

How to use GPT-4.5

GPT-4.5 was launched in February 2025 and was initially classified as a research preview. In the coming months, OpenAI will roll out broader availability.

As of the research preview phase GPT-4.5, there are several ways to use the model, including the following:

• ChatGPT Pro. For $200 a month, subscribers to OpenAI's top-tier ChatGPT service get limited access.
• ChatGPT Plus. For ChatGPT Plus users, initial restricted access begins in early March 2025.
• API access. Though costly, developers and organizations looking to integrate GPT-4.5 into their applications can access the model through OpenAI's API. The input cost is $75 for 1 million tokens, and the output cost is $150 per 1 million tokens.
• Microsoft Azure OpenAI Service. As with other OpenAI models, access is available in preview on the Azure OpenAI Service.

GPT-4o vs. GPT-4.5

When the initial GPT-4 release came out, it was the most powerful model in the world. Each successive model has continued to push capabilities and performance further. GPT-4.5 builds upon the foundations established by GPT-4 and GPT-4o. With GPT-4.5, OpenAI has introduced substantial enhancements in accuracy, emotional intelligence, conversational naturalness and alignment with user intent.

Sean Michael Kerner is an IT consultant, technology enthusiast and tinkerer. He has pulled Token Ring, configured NetWare and been known to compile his own Linux kernel. He consults with industry and media organizations on technology issues.