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Model

OpenAI o1

OpenAI o1 is the first reasoning model series from OpenAI, introduced in September 2024. It thinks through a long internal chain of thought before answering, and it was the base for later reasoning models such as o3.

Status DeprecatedModality Text, ImageContext (K tokens) 200 Era Generative AI for everyone

License
Proprietary
Access
API, App
Release date
Developer
OpenAI

What it is

OpenAI o1 is the first model series from OpenAI built to reason. According to OpenAI's system card, the o1 series is trained with large-scale reinforcement learning to reason using chain of thought, and it can produce a long chain of thought before answering the user [1][2]. A chain of thought is the step-by-step reasoning the model works through before it gives its final reply.

Background

The o1 series began with two models. On 12 September 2024 OpenAI introduced o1-preview and the smaller, faster and cheaper o1-mini, designed to spend more time thinking before responding, for complex tasks in science, coding and math [2]. The full o1 model was released on 5 December 2024, and an improved o1 followed on 17 December 2024 [2][3].

The model was reportedly known internally as "Q*" and later as "Strawberry" [2]. Its lineage continued with o3, which was announced in December 2024 and released in April 2025. DeepSeek-R1, released in January 2025, was benchmarked directly against o1 [2][4].

Key features

Through training, the models learn to refine their thinking process, try different strategies and recognise their mistakes [1]. OpenAI's safety approach for o1 is called deliberative alignment: the model reasons about OpenAI's safety policies in context before it responds to potentially unsafe prompts [1]. OpenAI said this reasoning gave the models state-of-the-art performance on certain risk benchmarks, such as resisting known jailbreaks and avoiding illicit advice [2].

For developers, API pricing for o1 was $15 per million input tokens and $60 per million output tokens, with a 200K-token context window [3]. OpenAI reported o1 at 48.9% on SWE-bench Verified and a Codeforces Elo of 1891. Later o3 surpassed both figures [4].

Under OpenAI's Preparedness Framework, o1 was rated overall medium risk. It was rated medium for persuasion and for CBRN (chemical, biological, radiological and nuclear) risk, and low for model autonomy and cybersecurity. Its o1-preview and o1-mini versions had the same overall rating [1].

Its place in the story

The o1 series marked a turn toward models that spend more compute on thinking before they answer. o1-preview was shut down in the API on 28 July 2025, and o1 was scheduled for shutdown on 23 October 2026 [5]. Its lineage shows how quickly reasoning models moved from a first release to a series of successors.

CapabilitiesLarge language modelsReasoningScience

Governance & standardsSafety & governance

Version history

22
  1. 2018
    • Jun 11, 2018 GPT-1

      GPT-1 was OpenAI's first generative pre-trained transformer, published in June 2018. It showed that one language model, pre-trained on unlabelled text and then fine-tuned, could improve results on many language tasks.

  2. 2019
    • Feb 14, 2019 GPT-2

      GPT-2 is a large language model that OpenAI announced in February 2019. Its largest version has 1.5 billion parameters. OpenAI first withheld the full model, then released it in stages through November 2019.

  3. 2020
    • May 28, 2020 GPT-3

      GPT-3 is an autoregressive language model with 175 billion parameters, described in a May 2020 paper. It could perform new tasks from a few examples in the prompt, without any gradient updates, and it was first offered through OpenAI's API.

  4. 2022
    • Mar 15, 2022 GPT-3.5 (text-davinci-002/003)

      GPT-3.5 is the family of OpenAI language models between GPT-3 and GPT-4, released through API models such as text-davinci-002 and text-davinci-003 and underlying the first version of ChatGPT.

  5. 2023
    • Mar 1, 2023 GPT-3.5 Turbo

      GPT-3.5 Turbo was the chat-optimised GPT-3.5 model OpenAI released through its API on 1 March 2023, priced at a tenth of the cost of earlier models and later replaced in ChatGPT by GPT-4o mini.

    • Mar 14, 2023 GPT-4

      GPT-4 is OpenAI's large multimodal model, released on 14 March 2023. It accepts image and text input, scored near the top of human test-takers on a simulated bar exam, and was succeeded by GPT-4 Turbo, GPT-4o and GPT-5.

    • Nov 6, 2023 GPT-4 Turbo

      GPT-4 Turbo is a cheaper, more capable version of OpenAI's GPT-4, announced on 6 November 2023 with a 128,000-token context window and lower API prices.

  6. 2024
    • May 13, 2024 GPT-4o

      GPT-4o is a multimodal model from OpenAI, released in May 2024, that takes text, audio, image and video as input and generates text, audio and image output within one neural network. It was removed from ChatGPT in February 2026.

    • Jul 18, 2024 GPT-4o mini

      A small, low-cost language model OpenAI released on 18 July 2024, priced far below GPT-4o and reported at 82% on MMLU; it replaced GPT-3.5 Turbo in ChatGPT on launch day.

    • Sep 12, 2024 OpenAI o1 · This page

      OpenAI o1 is the first reasoning model series from OpenAI, introduced in September 2024. It thinks through a long internal chain of thought before answering, and it was the base for later reasoning models such as o3.

  7. 2025
    • Feb 27, 2025 GPT-4.5

      GPT-4.5 is a large language model OpenAI released on 27 February 2025 under the code name "Orion". It was its largest chat model at the time, priced far above GPT-4o, and was retired from general availability within months.

    • Apr 14, 2025 GPT-4.1 (with mini and nano)

      OpenAI's April 2025 family of three API models — GPT-4.1, GPT-4.1 mini and GPT-4.1 nano — offering a context window of over a million tokens, low prices per token and stronger coding scores. It was succeeded by GPT-5.

    • Apr 16, 2025 OpenAI o3

      OpenAI's second-generation reasoning model, announced in December 2024 and released in April 2025, which posted large gains over o1 on science, software-engineering and competitive-programming benchmarks before being succeeded by GPT-5.

    • Aug 7, 2025 GPT-5

      GPT-5 is OpenAI's fifth GPT foundation model, released on 7 August 2025. It pairs a fast model with a deeper reasoning model and a router that chooses between them for each request.

    • Nov 12, 2025 GPT-5.1

      GPT-5.1 is an update to GPT-5 released by OpenAI on 12 November 2025. It added a warmer default personality with selectable styles, and its API version has been scheduled for shutdown in 2027.

    • Dec 11, 2025 GPT-5.2

      GPT-5.2 is a model family OpenAI released on 11 December 2025, with Instant, Thinking and Pro versions and a coding variant. It was aimed at professional work such as spreadsheets and presentations.

  8. 2026
    • Mar 5, 2026 GPT-5.4

      GPT-5.4 is a model OpenAI released on 5 March 2026 in Thinking and Pro versions. It added built-in computer use and improved deep research, and it was the model that succeeded GPT-5.2.

    • Apr 23, 2026 GPT-5.5

      GPT-5.5 is an OpenAI model released on 23 April 2026 as GPT-5.5 Thinking and Pro, with an API version the next day. It succeeded GPT-5.4 and had a cybersecurity variant in limited preview.

    • Jul 8, 2026 GPT-Live-1

      GPT-Live-1 is OpenAI's full-duplex voice model family, launched 8 July 2026, which lets ChatGPT listen and speak at the same time and replaced the earlier chained speech pipeline in ChatGPT Voice.

    • Jul 9, 2026 GPT-5.6 (Sol, Terra and Luna)

      OpenAI's three-model family released on 9 July 2026 — Luna, Terra and Sol, ordered from least to most capable — with Sol pitched as the company's strongest coding and agent model.

    • Sep 3, 2026 GPT-6 (Astra, Sol, Luna, Instant)

      GPT-6 is OpenAI's sixth-generation model family, launched from 3 September 2026 with GPT-6 Astra, followed by Sol, Luna and Instant. Astra was the first OpenAI model to reach its internal critical cybersecurity threshold.

    • Sep 29, 2026 GPT-6.1 (Sol and Terra)

      OpenAI's late-2026 model family: Sol, released at DevDay on 29 September 2026, and the faster, cheaper Terra on 26 October 2026. A planned Astra version was withheld over safety concerns.

20243

  1. ReleaseOpenAI launches ChatGPT Pro at $200 a month

    On 5 December 2024, OpenAI launched ChatGPT Pro, a $200-a-month plan with unlimited access to o1, o1-mini, GPT-4o, Advanced Voice and o1 pro mode; full o1 also arrived in ChatGPT the same day.

  2. UpdateOpenAI launches ChatGPT search

    On 31 October 2024 OpenAI launched ChatGPT search for Plus and Team users, evolving from the SearchGPT prototype. It drew on third-party search providers and content from many news publishers, and it became free without an account in February 2025.

  3. ReleaseOpenAI introduces o1, its first reasoning model series

    On 12 September 2024 OpenAI introduced o1-preview and o1-mini, its first reasoning models, designed to think longer before responding. The full o1 followed in December 2024, and Microsoft made the preview models available on Azure the same day.

Developed by1

OpenAI

Foundation for2

OpenAI o1-miniOpenAI o1 pro

Succeeded by1

OpenAI o3

Powers1

ChatGPT

Contributors1

Jakub Pachocki

Uses1

Chain of thought and reasoning models

Notes and sources

  1. OpenAI o1 System Cardhttps://arxiv.org/abs/2412.16720
  2. OpenAI o1https://en.wikipedia.org/wiki/OpenAI_o1
  3. OpenAI model release dateshttps://opper.ai/model-releases/openai
  4. OpenAI o3https://en.wikipedia.org/wiki/OpenAI_o3
  5. Deprecationshttps://developers.openai.com/api/docs/deprecations

Cite this page: OpenAI o1. TellWorld, https://www.tellworld.net/models/o1. Updated 2026-11-08