GPTGenerative Pre-trained Transformer — OpenAI's family of large language models from GPT-1 through GPT-5.-5.1 refined the unified GPTGenerative Pre-trained Transformer — OpenAI's family of large language models from GPT-1 through GPT-5.-5 stack with personality tuning and faster simple-task routing in Thinking mode. Codex-Mini and Codex-Max variants followed within a week — keeping OpenAIAn AI research company — created GPT, ChatGPT, DALL-E, and the o-series reasoning models. competitive as Google prepared GeminiGoogle's family of multimodal AI models — successors to PaLM and competitors to GPT and Claude. 3 and AnthropicAn AI safety company — creators of the Claude family of language models. readied Opus 4.5.

GPTGenerative Pre-trained Transformer — OpenAI's family of large language models from GPT-1 through GPT-5.-5.1 was OpenAIAn AI research company — created GPT, ChatGPT, DALL-E, and the o-series reasoning models.'s first major GPTGenerative Pre-trained Transformer — OpenAI's family of large language models from GPT-1 through GPT-5.-5 refresh with distinct Instant and Thinking modes.

Adaptive reasoningStep-by-step logical thinking in AI models — chain-of-thought before answering hard problems. effort made frontier models feel more conversational by default.