ChatGPT is about to become faster and more conversational as OpenAI upgrades its flagship model GPT-5 to GPT-5.1.

OpenAI announced two updates to the GPT-5 series: GPT-5.1 Instant and GPT-5.1 Thinking. Both models are now accessible on ChatGPT.

GPT-5.1 Instant, essentially the default and most-used model, is now “warmer, more intelligent, and better at following your instructions,” according to OpenAI. Meanwhile, GPT-5.1 Thinking is an advanced reasoning model that responds faster for simple tasks and more persistently on complex ones.

“We heard clearly from users that great AI should not only be smart, but also enjoyable to talk to,” OpenAI said in a blog post. “GPT-5.1 improves meaningfully on both intelligence and communication style.”

The company added that both models offer a way for users to “shape ChatGPT’s tone,” allowing people to control how the chat platform responds depending on the conversation they are having.

Both models were rolled out to ChatGPT Pro, Plus, Go and Business users, as well as the free tier. Those on the Enterprise and Edu plans will get a seven-day early-access toggle for the models before GPT-5.1 becomes the default model. OpenAI said the models can also be accessible through the API, both with adapted reasoning.

OpenAI has noted that it will soon update GPT-5 Pro to version 5.1.

Instant and Thinking models

The 5.1 tag reflects improvements to the base model, and OpenAI considers these part of the GPT-5 family, trained on the same stack and data as its reasoning models. The biggest difference between 5.1 and 5 is its more natural and conversational tone, OpenAI CEO for Applications Fidji Simo said in a Substack post.

“Based on early testing, it often surprises people with its playfulness while remaining clear and useful,” OpenAI said in its post.

Instant can use adaptive reasoning to help it decide when it needs to think about its answers, especially when it comes to more complicated questions. OpenAI noted that it has improved the model's instruction following, so that while it continues to respond quickly, it also directly addresses the user’s query.

Recent model releases, such as Baidu’s ERNIE-4.5-VL-28B-A3B-Thinking, have been outperforming GPT-5 in benchmarks like instruction-following.

GPT-5.1 Thinking can figure out on its own how much reasoning power it should devote to a prompt. It adapts to the type and complexity of a query, so it will take longer to answer a fuller, complex question than a simple summary request.

OpenAI said evaluations showed that GPT-5.1 Thinking spends less time and therefore uses fewer tokens on simple tasks compared to GPT-5, outperforming the base model in speed of response.

One thing enterprises should note is that GPT-5.1 Thinking answers “with less jargon and fewer undefined terms.” OpenAI said removing jargony responses makes Thinking more approachable when it comes to explaining technical concepts.

More personalization

Another big update to ChatGPT is increased personalization. This allows users to toggle between a friendly and authoritative chat platform experience in their conversations.

ChatGPT already allows users to choose preset options for model tone, but the new update expands these options “to better reflect the most common ways people use ChatGPT.”

Options include "default," "friendly" (formerly "listener"), "efficient" (previously "robot"), "professional," "candid" and "quirky." Two other personalities, "cynical" and "nerdy," remain unchanged.

“We think many people will find that GPT-5.1 does a better job of bringing IQ and EQ together, but one default clearly can’t meet everyone’s needs," Simo said. "That’s why we’re also making it easier to customize ChatGPT with a range of presets to choose from. The model has the same capabilities whether you select default or one of these options, but the style of its responses will differ — more formal or familiar, more playful or direct, more or less jargon or slang. Of course, eight personalities still don't cover the full range of human diversity, but we know from our research that many people prefer simple, guided control over too many settings or open-ended options."

People can also adjust how much ChatGPT uses emojis. OpenAI offers granular controls for responses and is experimenting with the ability to make the models more concise, warm or scannable.

Saving a rollout

OpenAI’s GPT-5 rollout was…less than perfect. While company executives, including CEO Sam Altman, touted the new model’s capabilities, a decision to initially sunset older and beloved models on ChatGPT was met with dissatisfaction. Worse yet, many early adopters found that GPT-5 didn’t perform better than older options in domains such as math, science and writing.

This led Altman to walk back some of his statements around model removal, blaming performance issues on GPT-5’s router. The router, which automatically directs queries to the most suited models, is not going away, as GPT-5.1 Auto will route prompts to the model type that can best answer queries.

OpenAI is careful to note that GPT-5 models Instant, Thinking and Pro are still available in ChatGPT’s model dropdown, although paid subscribers only have three months to compare these older versions with the 5.1 update. The sunset period for GPT-5, however, will not impact models like GPT-4o.

“Going forward, when we introduce new ChatGPT models, our approach is to give people ample space to evaluate what’s changed and share feedback, allowing us to continue innovating our frontier models while transitioning smoothly,” the company said. “Sunset periods will be communicated clearly and with plenty of advance notice.”

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