When OpenAI started giving private demonstrations of its new GPT-4 technology in late 2022, its skills shocked even the most experienced A.I. researchers. It could answer questions, write poetry and generate computer code in ways that seemed far ahead of its time.

More than two years later, OpenAI has released its successor: GPT-4.5. The new technology signifies the end of an era. OpenAI said GPT-4.5 would be the last version of its chatbot system that did not do “chain-of-thought reasoning.”

After this release, OpenAI’s technology may, like a human, spend a significant amount of time thinking about a question before answering, rather than providing an instant response.

GPT-4.5, which can be used to power the most expensive version of ChatGPT, is unlikely to generate as much excitement at GPT-4, in large part because A.I. research has shifted in new directions. Still, the company said the technology would “feel more natural” than its previous chatbot technologies.

“What sets the model apart is its ability to engage in warm, intuitive, naturally flowing conversations, and we think it has a stronger understanding of what users mean when they ask for something,” said Mia Glaese, vice president of research at OpenAI.

In the fall, the company introduced technology called OpenAI o1, which was designed to reason through tasks involving math, coding and science. The new technology was part of a wider effort to build A.I. that can reason through complex tasks. Companies like Google, Meta and DeepSeek, a Chinese start-up, are developing similar technologies.