2018 – 2026

ChatGPT Versions

OpenAI's current ChatGPT flagship is GPT-5.5, released April 23, 2026 (API strings gpt-5.5 and gpt-5.5-pro), with GPT-5.5 Instant shipping May 5, 2026 as the new ChatGPT default (API string chat-latest). I track every OpenAI release here — from GPT-1 in June 2018 onward — with API model strings, ship dates, and the major changes per version, because the model strings and ship dates change too often for marketing pages to keep up. Below the table: the 2015 founding, the Musk departure, the November 2023 board episode, the 2024 leadership exodus, the for-profit conversion fight, the GPT-5 unified-router moment in August 2025 followed by the rapid post-GPT-5 cadence (5.1 / 5.2 / 5.3-Codex / 5.4 / 5.5), and the lawsuits.

Family & status

Family

GPT — the main chat models, from GPT-3.5 onward
Reasoning — the o-series; spend tokens thinking before answering
Pre-ChatGPT — GPT-1 / 2 / 3 and the InstructGPT / text-davinci-* base models

Status

Current — actively recommended; the latest in its family
Available — still served via API but superseded
Legacy — deprecated or sunset; no longer served
Research preview — available only as a preview, not GA

ChatGPT version table

Model
GPT-5.5
gpt-5.5, gpt-5.5-pro, gpt-5.5-instant (chat-latest)
GPT
Current
Apr 23, 2026
Latest. Six weeks after 5.4. The "AI super-app" framing — one model that writes code, browses, builds spreadsheets, edits documents, drives software end-to-end. GPT-5.5 Instant arrived May 5, 2026 as the new ChatGPT default.
  • Released April 23, 2026 in ChatGPT and Codex; available in the API as gpt-5.5 and gpt-5.5-pro from April 24, 2026.
  • Positioned as OpenAI’s "smartest and most intuitive model yet" — understands intent faster, carries more of the work itself across writing / debugging code, online research, data analysis, document and spreadsheet creation, software operation.
  • Six weeks after GPT-5.4 — the cadence between OpenAI releases has compressed dramatically through late 2025 / early 2026; releases now look more like software updates than model launches.
  • Rolling out to Plus, Pro, Business, and Enterprise tiers in ChatGPT and Codex; gpt-5.5-pro is restricted to Pro / Business / Enterprise.
  • GPT-5.5 Instant (May 5, 2026) — ChatGPT’s new default model, replacing GPT-5.3 Instant for all tiers and available in the API as chat-latest. OpenAI reports 52.5% fewer hallucinated claims than GPT-5.3 Instant on high-stakes prompts (medicine / law / finance), 30.2% fewer words and 29.2% fewer lines per response, and personalization from past chats, files, and connected Gmail rolling out to Plus and Pro on web first. GPT-5.3 Instant remains accessible to paid users via model configuration for three months before retirement. See the GPT-5.5 Instant announcement.
  • GPT-5.5-Cyber (May 7, 2026) — a more-permissive security-tuned variant opened as a limited preview through OpenAI’s Trusted Access for Cyber (TAC) program, available only to vetted defenders (government, critical-infrastructure operators, security vendors, financial institutions), not as a generally-served API model string. Tuned for secure code review, vulnerability triage, malware analysis, detection engineering, and patch validation; TAC members accessing the most permissive cyber models must enable Advanced Account Security from June 1, 2026. See the Trusted Access for Cyber announcement.
  • See the OpenAI announcement and the GPT-5.5 system card.
Model
GPT-5.4
gpt-5.4, gpt-5.4-thinking, gpt-5.4-pro, gpt-5.4-mini, gpt-5.4-nano
GPT
Available
Mar 5, 2026
First general-purpose model with native state-of-the-art computer-use. 1M-token context. 33% fewer factual errors vs. 5.2.
  • Released March 5, 2026 across ChatGPT, the API, and Codex.
  • First general-purpose model with native, state-of-the-art computer-use capabilities — agents can operate computers and carry out complex multi-application workflows.
  • 1M-token context across the line.
  • GPT-5.4 Thinking can provide an upfront plan of its reasoning for mid-response adjustments; deep web research is improved for highly specific queries.
  • 33% reduction in factual errors compared to GPT-5.2 on individual claims.
  • Mini and nano variants shipped alongside the flagship; GPT-5.4 Pro restricted to Pro and Enterprise plans.
  • See the OpenAI announcement.
Model
GPT-5.3 Instant
gpt-5.3-chat-latest
GPT
Available
Mar 3, 2026
ChatGPT default update focused on conversational quality — fewer dead ends, caveats, and emoji; richer web-search results. Superseded by GPT-5.5 Instant on May 5, 2026.
  • Released March 3, 2026 as the ChatGPT default model update following GPT-5.3-Codex; served in the API as gpt-5.3-chat-latest.
  • Focused on the parts of the ChatGPT experience users feel every day: tone, relevance, and conversational flow — problems that don't always show up in benchmarks but shape whether ChatGPT feels helpful or frustrating.
  • Delivers more accurate answers and richer, better-contextualized results when searching the web; reduces unnecessary dead ends, caveats, and overly declarative phrasing.
  • Addresses user feedback about ChatGPT being "too cringe" — specifically cuts gratuitous emoji, excessive hedging, and hollow affirmations.
  • Superseded by GPT-5.5 Instant on May 5, 2026, which became the new ChatGPT default; GPT-5.3 Instant remains accessible to paid users via model configuration for three months before retirement.
  • See the OpenAI announcement.
Model
GPT-5.3-Codex
gpt-5.3-codex
GPT
Available
Feb 5, 2026
Codex-specialized intermediate. State-of-the-art on SWE-Bench Pro and Terminal-Bench 2.0. 25% faster than 5.2-Codex. (OpenAI shipped a separate GPT-5.3 Instant chat model two days later.)
  • Released February 5, 2026 as a Codex-specialized variant; the general-purpose chat update in this cycle was GPT-5.3 Instant, released two days later on March 3, 2026.
  • Combines the frontier coding performance of GPT-5.2-Codex with the reasoning and professional-knowledge improvements of GPT-5.2 in a single model.
  • State-of-the-art on SWE-Bench Pro — the contamination-resistant, multi-language successor to SWE-bench Verified that spans four languages instead of Python alone.
  • Significantly improves on the previous state of the art on Terminal-Bench 2.0.
  • ~25% faster than 5.2-Codex.
  • See the OpenAI announcement.
Model
GPT-5.2
gpt-5.2, gpt-5.2-thinking, gpt-5.2-pro, gpt-5.2-codex
GPT
Available
Dec 11, 2025
Three modes (Instant / Thinking with extended-thinking / Pro). State of the art on FrontierMath Tier 1–3. Better at spreadsheets, financial modeling, presentations. gpt-5.2-chat-latest shutdown Aug 10, 2026; gpt-5.2-codex shutdown Jul 23, 2026.
  • Released December 11, 2025 in three modes: gpt-5.2 (instant), gpt-5.2-thinking (with optional extended thinking), and gpt-5.2-pro (reasoning, restricted tier).
  • Codex-specialized variant gpt-5.2-codex shipped alongside as a coding-focused fork.
  • State-of-the-art on FrontierMath Tier 1–3 (40.3% solved by GPT-5.2 Thinking) — the expert-level mathematics evaluation.
  • Substantially better at spreadsheet creation, financial modeling, presentation generation, and multi-step project execution.
  • See the OpenAI announcement.
Model
GPT-5.1
gpt-5.1, gpt-5.1-instant, gpt-5.1-thinking
GPT
Legacy
Nov 12, 2025
First post-GPT-5 update. Instant and Thinking modes; eight personality presets; apply_patch and shell tools for code agents. gpt-5.1-chat-latest and the codex snapshots shut down Jul 23, 2026.
  • Released November 12, 2025 in ChatGPT (two more variants followed November 19); arrived in the API on November 13, 2025.
  • Two new modes: gpt-5.1-instant (snappy default) and gpt-5.1-thinking (deliberate reasoning), with the model varying its compute per query.
  • Eight personality presets — customizable response style; users pick a tone rather than prompt-engineering one.
  • Markedly faster on easy queries (e.g. "show an npm command for global packages": ~2s on 5.1 vs. ~10s on 5.0).
  • Two new agent tools: apply_patch for reliable code edits, shell for running shell commands. Built with input from Cursor, Cognition, Augment Code, Factory, and Warp.
  • See the OpenAI developer announcement.
Model
GPT-5
gpt-5
GPT
Legacy
Aug 7, 2025
Unifies the GPT and reasoning lines behind a router that chooses between fast-answer and thinking modes per query. The headline release of 2025. gpt-5 Instant/Thinking retired from ChatGPT Feb 13, 2026; gpt-5-chat-latest and gpt-5-codex API snapshot shutdown scheduled Jul 23, 2026.
  • Released August 7, 2025; positioned by OpenAI as a single product surface that routes between fast and thinking responses depending on the query, ending the user-facing GPT / o-series split.
  • Unified routing — the model decides whether to answer immediately or invoke an internal reasoning pass; chat.openai.com no longer surfaces a separate model picker for most users.
  • Available across gpt-5, gpt-5-mini, and gpt-5-nano tiers in the API; pricing positioned aggressively against Anthropic's Sonnet line.
  • Sam Altman publicly conceded in the months leading up to the release that the prior naming (4 / 4 Turbo / 4o / 4o mini / 4.1) had become unmanageable; GPT-5 was framed in part as a naming reset.
  • Default model on chatgpt.com from launch; replaced GPT-4o as the routed default within the consumer app.
Model
o3-pro
o3-pro
Reasoning
Available
Jun 10, 2025
o3 with more compute for higher reliability. Consistently preferred over o3 in expert evaluations across science, education, coding, business, and writing.
  • Released June 10, 2025 for ChatGPT Pro and Team users (replacing o1-pro); Enterprise and Edu access followed the next week. Available in the developer API as of the same day.
  • Uses the same underlying model as o3 but allocates more compute at inference time, producing more reliable responses at the cost of significantly higher latency — some requests take several minutes.
  • In expert evaluations, reviewers consistently preferred o3-pro over o3 in every tested category — especially science, education, programming, business, and writing help — rating it higher for clarity, comprehensiveness, instruction-following, and accuracy.
  • Has access to tools: web browsing, file analysis, visual reasoning, Python execution, and personalized memory-based responses.
  • Outperformed Google Gemini 2.5 Pro on AIME 2024 (math) and Anthropic Claude 4 Opus on GPQA Diamond (PhD-level science) in OpenAI’s internal testing at launch.
  • Priced at $20 / $80 per million input / output tokens in the API — ten times the cost of o3, positioning it for challenging queries where reliability matters more than speed. Available in the Responses API only.
  • See the OpenAI model release notes and the TechCrunch report.
Model
GPT-4.1
gpt-4.1, gpt-4.1-mini, gpt-4.1-nano
GPT
Legacy
Apr 14, 2025
Coding-focused refresh of the GPT line. 1M-token context. Mini and nano sub-tiers for cost-sensitive calls. Retired from ChatGPT Feb 13, 2026; gpt-4.1-nano snapshot shutdown scheduled Oct 23, 2026.
  • Released April 14, 2025 in three sizes: gpt-4.1, gpt-4.1-mini, and gpt-4.1-nano.
  • Substantial coding-quality gains over GPT-4o on SWE-bench-style benchmarks; positioned as the developer-API model line.
  • 1,000,000-token context window across all three sizes — matching the long-context expansions of the period.
  • Initially API-only; chat.openai.com kept GPT-4o as the routed default until GPT-5 took over four months later.
  • The naming jump from GPT-4o back to GPT-4.1 contributed to the “the names are unmanageable” framing that GPT-5 partly answered.
Model
GPT-4.5
gpt-4.5-preview
GPT
Legacy
Feb 27, 2025
OpenAI's largest GPT pre-training run to date, shipped as a research preview. Tuned for naturalness, emotional intelligence, and reduced hallucination rather than chain-of-thought reasoning. API access ended Jul 14, 2025; removed from ChatGPT Jun 27, 2026.
  • Released February 27, 2025 as a research preview (gpt-4.5-preview), internally codenamed “Orion” — the last and largest model in OpenAI's pure pretraining-scaling line, before the reasoning track became the focus.
  • Scaling, not reasoning — no chain-of-thought; the pitch was a warmer, more natural model with broader world knowledge, stronger emotional intelligence, and a lower hallucination rate than GPT-4o.
  • Launched at a steep price ($75 / $150 per million input / output tokens) and gated to the Pro tier first, then Plus — reflecting the model's size and compute cost.
  • API wind-down — OpenAI removed gpt-4.5-preview from the API on July 14, 2025, framing it as a preview that had served its purpose; it stayed in ChatGPT until the June 27, 2026 retirement (announced June 3, 2026 with a 30-day sunset).
  • Part of the “the names are unmanageable” period — a GPT-4.5 slotted between GPT-4o and the reasoning models that the eventual GPT-5 unification was meant to clean up.
Model
o4-mini
o4-mini
Reasoning
Legacy
Apr 16, 2025
Cheap and fast reasoning model. Closes most of the gap to o3 at a fraction of the cost. Tool use during chain-of-thought. Retired from ChatGPT Feb 13, 2026; API snapshot shutdown scheduled Oct 23, 2026.
  • Released April 16, 2025; the smaller, cheaper companion to o3 in the “next-gen reasoning” April 2025 wave.
  • Tool use during reasoning — the model can call tools (web search, code execution, file reads) inside its chain-of-thought rather than only at the boundary.
  • Closes most of the quality gap with o3 at a small fraction of its cost; the routine recommendation for high-volume reasoning workloads.
  • The naming choice (o4-mini, not o3.5 or o4) follows the same “skip the GA flagship and ship the mini” pattern as o3-mini four months earlier.
Model
o3
o3
Reasoning
Legacy
Apr 16, 2025
GA reasoning flagship. Frontier scores on math and coding benchmarks. Tool-use-in-reasoning by default. Demoted to legacy following o3-deep-research deprecation (Apr 22, 2026, shutdown Jul 23, 2026); deep-research snapshots replaced by gpt-5.5-pro.
  • Released April 16, 2025 as the GA flagship of the reasoning line, alongside o4-mini.
  • Frontier-grade scores on competition math (AIME) and the hardest coding benchmarks at launch.
  • Replaced o1 as the recommended top-of-line reasoning model for paying API users; o1 demoted to Available.
  • The model that the “reasoning works as a research direction” framing of late 2024 onward is most often pinned to in retrospect.
Model
o3-mini
o3-mini
Reasoning
Legacy
Jan 31, 2025
First non-preview reasoning model. Shipped two months ahead of the GA o3 flagship and free in ChatGPT.
  • Released January 31, 2025; the first reasoning model OpenAI shipped outside the original o1 preview / GA pair.
  • Made reasoning available to free-tier ChatGPT users for the first time, with rate limits.
  • Three reasoning effort levels (low, medium, high) exposed via the API — the convention later carried forward to GPT-5.
  • Superseded by o4-mini in April 2025; demoted to Legacy on OpenAI's deprecation schedule.
Model
o1
o1
Reasoning
Legacy
Dec 5, 2024
GA release of the o-series flagship. Replaced o1-preview. The first reasoning model on the OpenAI API at general availability. Deprecated Apr 22, 2026; API shutdown scheduled Oct 23, 2026.
  • Released December 5, 2024 as the GA replacement for o1-preview, on the “12 Days of OpenAI” launch event.
  • Substantial gains over o1-preview on most reasoning benchmarks; vision support added in the same release.
  • First “Pro mode” debut on chatgpt.com — a $200/mo tier that runs o1 with much higher compute per response.
  • Superseded by o3 in April 2025; still served via the API.
Model
o1-mini
o1-mini
Reasoning
Legacy
Sep 12, 2024
Smaller, cheaper, faster reasoning companion to o1-preview. Coding-focused; strong on STEM benchmarks at a fraction of the price.
  • Released September 12, 2024 alongside o1-preview as the first pair of public reasoning models.
  • Optimized for STEM and coding tasks; comparable to o1-preview on coding evaluations at a meaningful price drop.
  • The launch of the “Strawberry” line publicly — OpenAI's internal codename that had leaked widely in the months prior.
  • Superseded by o3-mini in January 2025; demoted to Legacy.
Model
o1-preview
o1-preview
Reasoning
Legacy
Sep 12, 2024
First public reasoning model. Trained to think step-by-step before answering. Set a new frontier on competition math and hard coding.
  • Released September 12, 2024 as a research preview — the first OpenAI model trained with chain-of-thought as a first-class capability rather than a prompt-engineering technique.
  • Frontier scores on AIME (American Invitational Mathematics Examination) and Codeforces at launch — a step-change on the hardest benchmarks.
  • Slower and more expensive per token than GPT-4o, with the trade-off framed as “latency for thinking”.
  • Superseded by the GA o1 in December 2024; demoted to Legacy.

The reasoning era — September 12, 2024. Above this line: the Reasoning family (o1-preview, o1, o1-mini, o3, o3-mini, o4-mini) and the post-reasoning GPT models (GPT-4.1, GPT-4.5, GPT-5) that followed. Below: the original GPT chat line from GPT-3.5 / ChatGPT through GPT-4o. The split lasted just under a year before GPT-5 unified the two surfaces.

Model
GPT-4o mini
gpt-4o-mini
GPT
Legacy
Jul 18, 2024
Cheaper, faster GPT-4o for high-volume calls. Replaced GPT-3.5 Turbo as the recommended cheap-tier chat model. Retired from ChatGPT Feb 13, 2026; API access via dated snapshot continues.
  • Released July 18, 2024 as the small, cheap companion to GPT-4o.
  • Pricing at $0.15 / $0.60 per million input / output tokens at launch — an order of magnitude cheaper than GPT-3.5 Turbo had been when it shipped.
  • Quickly became the routine recommendation for classification, routing, and high-volume agent steps.
  • Multimodal (vision and text input) on the same surface as GPT-4o; voice support added later.
Model
GPT-4o
gpt-4o
GPT
Legacy
May 13, 2024
Native multimodal — text, image, and audio in a single model. The default ChatGPT model for most of 2024 / 2025. Retired from ChatGPT Feb 13, 2026; chatgpt-4o-latest API snapshot removed Feb 17, 2026; gpt-4o-2024-05-13 snapshot shutdown scheduled Oct 23, 2026.
  • Released May 13, 2024; the “o” standing for “omni,” reflecting native handling of text, image, and audio in a single model rather than the prior speech-to-text-to-LLM pipeline.
  • Advanced Voice Mode demoed at launch and rolled out incrementally through the second half of 2024 — conversational latency low enough that natural turn-taking became practical.
  • Replaced GPT-4 Turbo as the default model on chatgpt.com and stayed the routed default until GPT-5 took over fifteen months later.
  • The Sky-voice / Scarlett Johansson controversy (May 2024) erupted around this launch; OpenAI removed the Sky voice within days.
  • Free-tier ChatGPT users gained access to a frontier multimodal model for the first time, with daily limits.
Model
GPT-4 Turbo
gpt-4-turbo
GPT
Legacy
Nov 6, 2023
128k context. Cheaper than original GPT-4. Custom GPTs and the Assistants API launched on the same DevDay. Eleven days later the board fired Altman.
  • Announced November 6, 2023 at DevDay 2023; the same event that launched Custom GPTs, the GPT Store, and the Assistants API.
  • 128,000-token context window — a sixteen-times increase over the original GPT-4 8k.
  • Substantially cheaper per token than GPT-4 at launch; the price drop set the cadence for the GPT-4 line through 2024.
  • Eleven days after this DevDay, the OpenAI board fired Sam Altman — the November 2023 episode covered in the prose history below.
  • Superseded by GPT-4o in May 2024; demoted to Legacy on the deprecation schedule.
Model
GPT-4
gpt-4
GPT
Legacy
Mar 14, 2023
First multimodal frontier model. “Passes the bar exam.” Plugins and Code Interpreter shipped within weeks.
  • Released March 14, 2023; the same week Anthropic shipped Claude 1 in limited access.
  • First OpenAI model with image input (rolled out incrementally over the following months).
  • The “passes the bar exam in the 90th percentile” framing in the GPT-4 Technical Report drove the mainstream coverage; later research disputed the methodology, but the framing stuck.
  • Initial 8k context window with a separate 32k variant; both later superseded by Turbo's 128k.
  • Plugins launched March 23, 2023 (deprecated 2024 in favor of Custom GPTs and tool calling). Code Interpreter followed in July 2023.
  • Superseded by GPT-4 Turbo in November 2023 and GPT-4o in May 2024; deprecated.
Model
GPT-3.5 / ChatGPT launch
gpt-3.5-turbo
GPT
Legacy
Nov 30, 2022
ChatGPT launched as a “low-key research preview” on top of GPT-3.5. One million users in five days, a hundred million in two months.
  • Released November 30, 2022; OpenAI framed it publicly as a “low-key research preview,” an internal expectation that turned out to be wrong by orders of magnitude.
  • One million users in five days, a hundred million in two months — at the time, the fastest-growing consumer application in history.
  • The model was a fine-tuned descendant of the InstructGPT-era text-davinci-* base; the gpt-3.5-turbo snapshot came in March 2023 and became the default chat-completion model for most of 2023.
  • The product (ChatGPT) was distinct from the model name (GPT-3.5) from day one — the start of the naming confusion that would compound through GPT-4 / 4 Turbo / 4o / 4.1.

ChatGPT launches — November 30, 2022. Above this line: the consumer-product era. OpenAI became a household name within weeks, the company's center of gravity shifted from research lab to product organization, and every model release after this point was framed in part as “what does this change for ChatGPT.” Below: the Pre-ChatGPT era — GPT-1 / 2 / 3 and the InstructGPT / text-davinci base models that quietly defined the technical lineage before the consumer launch.

Model
InstructGPT / text-davinci series
text-davinci-001, text-davinci-002, text-davinci-003
Pre-ChatGPT
Legacy
Jan 27, 2022
RLHF arrives. The technical predecessor to ChatGPT. Three text-davinci-* snapshots through 2022.
  • InstructGPT introduced in “Training language models to follow instructions with human feedback” (Ouyang et al., 2022) — the public arrival of RLHF as the technique that turned base GPT-3 into a usable assistant.
  • The text-davinci-001, text-davinci-002, and text-davinci-003 snapshots through 2022 were the production face of the InstructGPT line, available on the OpenAI API to developers a year before ChatGPT launched.
  • Technically GPT-3.5-family base models; rolled into a single row here rather than per-snapshot because the differences were incremental and the distinct rows belong to the consumer-facing products that came after.
  • All snapshots later sunset as gpt-3.5-turbo took over.
Model
GPT-3
davinci, curie, babbage, ada
Pre-ChatGPT
Legacy
May 28, 2020
175B parameters. “Language Models are Few-Shot Learners.” The first GPT to feel mainstream-newsworthy. API-only via the Playground.
  • Released May 28, 2020; the paper is “Language Models are Few-Shot Learners” (Brown et al., 2020).
  • 175 billion parameters — over a hundred-fold larger than GPT-2; the central illustration of the “scale matters” thesis.
  • Distributed via the OpenAI API (waitlist, then Playground) under the four engine names davinci / curie / babbage / ada — the first commercial product OpenAI shipped.
  • Used few-shot prompting as the default interaction pattern; chat-style instruction-following had to wait for InstructGPT.
  • Microsoft announced an exclusive license to the underlying weights in September 2020, separate from API access.
Model
GPT-2
gpt2 / gpt2-medium / gpt2-large / gpt2-xl
Pre-ChatGPT
Legacy
Feb 14, 2019
Initially withheld over “misuse concerns,” then released in stages through November 2019. 1.5B parameters.
  • Announced February 14, 2019; the paper is “Language Models are Unsupervised Multitask Learners” (Radford et al., 2019).
  • Initial release withheld the largest 1.5B-parameter model over “concerns about malicious applications.” OpenAI staged the release through 2019, with the full model published in November.
  • The decision to withhold became one of the more debated episodes in the AI-safety conversation of the period; the staged release set the template for “responsible disclosure” framings that later returned with GPT-4 and beyond.
  • 1.5B parameters at the largest size; meaningful generative coherence at multi-paragraph length was novel at the time.
  • Open-weights release means GPT-2 is still widely usable today via Hugging Face and similar surfaces.
Model
GPT-1
openai-gpt
Pre-ChatGPT
Legacy
Jun 11, 2018
The original GPT. “Improving Language Understanding by Generative Pre-Training.” 117M parameters. The start of the lineage.
  • Released June 11, 2018; the paper is “Improving Language Understanding by Generative Pre-Training” (Radford et al., 2018).
  • 117 million parameters; trained on the BookCorpus dataset.
  • Established the “generative pre-training, then fine-tune” recipe that every later GPT extended.
  • Technically a Transformer-decoder architecture, following Vaswani et al.'s “Attention is All You Need” (2017) by less than a year.
  • Open-weights release; the model is still inspectable today, more interesting now as the ancestor of the line than as a usable system.

Click any row to expand. Each row has a stable id for sharing — e.g. /ai/chatgpt/versions/#gpt-5, #gpt-4o, #o1-preview. The current model list and lifecycle status is at platform.openai.com/docs/models; deprecation timelines at platform.openai.com/docs/deprecations.

The 2015 founding

OpenAI was announced on December 11, 2015 as a nonprofit AI research lab. The cofounders were Sam Altman, Elon Musk, Greg Brockman, Ilya Sutskever (recruited from Google Brain), John Schulman, Wojciech Zaremba, Andrej Karpathy, Pamela Vagata, Trevor Blackwell, and Vicki Cheung. The launch announcement listed an initial $1 billion in pledges from Altman, Musk, Reid Hoffman, Peter Thiel, Y Combinator Research, Microsoft, Amazon Web Services, and Infosys; in practice, most pledges were never fully called.

The stated mission was to ensure that artificial general intelligence “benefits all of humanity,” with research published openly. The legal vehicle was a 501(c)(3) nonprofit. Both of those framings would shift materially over the following decade.

The Musk departure (2018)

Elon Musk left the OpenAI board in February 2018, citing a conflict of interest with Tesla's AI work. He stopped funding shortly after. Internal accounts later reported in NYT and The Information describe an unsuccessful attempt by Musk to take direct control of the lab in the prior period. The departure is the load-bearing prelude to Musk v. Altman in 2024 and to xAI's founding in 2023.

The capped-profit conversion (2019)

In March 2019, OpenAI created OpenAI LP, a “capped-profit” subsidiary, to raise commercial capital without abandoning the nonprofit charter. The cap on returns to investors was reportedly set at one hundred times their investment, with profits beyond that flowing back to the nonprofit. Microsoft invested $1 billion in July 2019, with Azure becoming a key cloud commitment.

The capped-profit structure is the structural origin of essentially every subsequent governance dispute — the November 2023 board episode, the for-profit conversion fight, the lawsuits framing the conversion as a betrayal of the founding mission.

The GPT lineage and InstructGPT

The technical lineage runs GPT-1 (June 2018) on BookCorpus, GPT-2 (Feb 2019) with the staged release, GPT-3 (May 2020) at 175B parameters, and InstructGPT (Jan 2022) introducing RLHF as the technique that turned a base language model into a usable assistant. The InstructGPT paper is the technical predecessor to ChatGPT itself, even though the consumer product launched ten months later under different framing.

ChatGPT launches (November 30, 2022)

ChatGPT launched as a “low-key research preview” on top of GPT-3.5 on November 30, 2022. OpenAI's internal expectation was for steady research-community adoption; reality was one million users in five days, a hundred million in two months — at the time, the fastest-growing consumer application in history.

The launch is the inflection point of the entire post-2015 history of OpenAI. The company's center of gravity shifted from research lab to product organization within weeks; every governance and financial dispute that followed was downstream of the consumer success that arrived faster than anyone had planned for.

The Microsoft expansion (January 2023)

In January 2023, Microsoft announced a multi-year, multibillion-dollar investment widely reported as $10 billion — an extension of the 2019 commitment. Azure became the exclusive cloud provider for OpenAI's training and inference. The relationship has been the financial backbone of the company through at least 2025, and is the recurring subtext of the for-profit conversion fight, the AGI-clause dispute, and the various antitrust filings that have followed.

GPT-4 and the multimodal era (March 2023)

GPT-4 launched on March 14, 2023 with image input, far stronger reasoning, and the “passes the bar exam in the 90th percentile” framing that drove most of the mainstream coverage. Plugins followed two weeks later; Code Interpreter in July. The plugin surface was deprecated in 2024 in favor of Custom GPTs and tool calling, but it set the early template for “LLM as orchestrator of external services.”

DevDay 2023 (November 6, 2023)

OpenAI's first DevDay launched GPT-4 Turbo (128k context, lower price), Custom GPTs, the GPT Store, the Assistants API, and a handful of tooling improvements. The conference was widely treated at the time as a victory lap. Eleven days later, the board fired Altman.

The November 2023 board episode (Nov 17 – 21, 2023)

On November 17, 2023, the OpenAI board — Helen Toner, Tasha McCauley, Adam D'Angelo, and Ilya Sutskever — fired Sam Altman, citing a loss of confidence in his communications with the board. Greg Brockman resigned in protest the same day. Mira Murati was named interim CEO; within twenty-four hours she was reportedly negotiating Altman's return.

On November 19, the board appointed Emmett Shear (former Twitch CEO) as the second interim CEO. Roughly seven hundred of OpenAI's seven hundred and seventy employees signed an open letter threatening to follow Altman to Microsoft if the board did not resign and reinstate him. Microsoft publicly offered to hire Altman, Brockman, and any departing employees to lead a new AI research division.

On November 21 — five days after the firing — Altman returned as CEO. The board was reconstituted with Bret Taylor as chair, Larry Summers, and D'Angelo continuing. Toner, McCauley, and Sutskever were off the board. Helen Toner has since described her account in a TED talk and an academic paper. Contemporaneous reporting in NYT, WSJ, Bloomberg, and The Information remains the most thorough public record. For the full tick-tock and the participants' subsequent framings, see the dedicated November 2023 board episode section on the OpenAI Leadership page.

The 2024 leadership exodus

The year after the board episode produced the most concentrated departure of senior leadership in OpenAI's history. Andrej Karpathy left in February 2024 (later founding Eureka Labs). Ilya Sutskever left in May 2024 and founded Safe Superintelligence Inc. Jan Leike left the same week and joined Anthropic, citing concerns about OpenAI's safety culture in a public thread that read as an indictment. The superalignment team was dissolved within days.

John Schulman, an OpenAI cofounder and the original lead on RLHF and on ChatGPT itself, left in August 2024 for Anthropic, then later moved to Mira Murati's startup. Mira Murati herself left in September 2024 and founded Thinking Machines Lab; Bob McGrew (Chief Research Officer) and Barret Zoph (VP Research) left the same week. Greg Brockman took an extended sabbatical from May to August 2024 and returned.

After the October 2025 recapitalization, the operating senior team consists of Sam Altman (CEO), Greg Brockman (President), Sarah Friar (CFO), and Mark Chen (SVP Research / Chief Research Officer); long-time COO Brad Lightcap moved to special projects in spring 2026. Bret Taylor chairs the board of the controlling OpenAI Foundation. A second cluster of departures landed in April 2026 — Kevin Weil, Bill Peebles, and Srinivas Narayanan — alongside the wind-down of side projects (Sora, OpenAI for Science). The current roster should be re-verified at every refresh given the volatility of the prior period. For the deeper treatment — primary-source links per departure, the “where they went next” table, and the Anthropic-rebalance pattern — see the superalignment exodus on the OpenAI Leadership page.

The Sky / Scarlett Johansson voice (May 2024)

At the GPT-4o launch demo on May 13, 2024, OpenAI presented a voice named “Sky” that listeners and Scarlett Johansson herself perceived as a deliberate echo of her performance in the 2013 film Her. Johansson stated publicly that she had previously declined OpenAI's offer to voice the assistant. OpenAI removed the Sky voice within days. The episode is recounted briefly here because it bears on the launch row and on how OpenAI's public-facing decisions were perceived in the period; it is not enlarged into its own section.

The for-profit conversion (2024 – 2025)

Through 2024 and 2025, OpenAI publicly worked toward converting the capped-profit LP into a public-benefit corporation. The transaction closed on October 28, 2025: the operating subsidiary became OpenAI Group PBC, controlled by the renamed nonprofit OpenAI Foundation (which holds about 26% equity, worth roughly $130 billion at closing); Microsoft holds about 27% (~$135 billion). Microsoft and OpenAI amended the agreement again on April 27, 2026 to make Microsoft's IP license non-exclusive and to recut the revenue-share. The Musk legal challenge survived the closing — Musk v. Altman went to trial in April 2026, and on May 18, 2026 the advisory jury (its verdict adopted by Judge Yvonne Gonzalez Rogers) found in favor of OpenAI, ruling Musk's claims time-barred by the three-year statute of limitations rather than reaching the merits; Musk called it a “calendar technicality” and said he would appeal. For the structural detail and the cross-reference to the docket, see the for-profit conversion fight on the OpenAI Leadership page.

The reasoning era (September 2024 onward)

o1-preview and o1-mini in September 2024 introduced the “thinks before answering” pattern as a first-class model capability rather than a prompt-engineering technique. o1 went GA in December 2024, o3-mini in January 2025, and the GA o3 and o4-mini in April 2025 alongside the GPT-4.1 line. GPT-5 in August 2025 unified the GPT and reasoning surfaces behind a single router that decides per-query whether to answer immediately or invoke reasoning. The split as a user-visible product distinction lasted just under a year.

The lawsuits

The litigation around OpenAI through 2024 – 2026 is unusually wide-ranging. The case-name links below jump to the per-case rows on the dedicated OpenAI Lawsuits page, which carries plaintiffs, procedural milestones, motion-to-dismiss outcomes, and primary-source links per case.

  • Musk v. Altman, Brockman, OpenAI, et al. Filed February 29, 2024 in California state court alleging breach of the founding agreement; voluntarily dismissed June 2024; refiled August 2024 in N.D. Cal. with additional claims including RICO. Tried in spring 2026; on May 18, 2026 the advisory jury found for OpenAI on statute-of-limitations grounds and Musk signaled an appeal — verify the current docket status on the lawsuits page.
  • The New York Times Company v. Microsoft Corp. & OpenAI (S.D.N.Y., filed December 27, 2023). The flagship publisher copyright case, alleging mass copying of Times articles into the training corpus and reproduction of paywalled content in outputs. A motion-to-dismiss ruling in 2024 narrowed but did not gut the case.
  • Authors Guild v. OpenAI (S.D.N.Y., filed September 2023, consolidated with the author class actions). Plaintiffs include George R.R. Martin, John Grisham, Jodi Picoult, and others.
  • The Tremblay / Silverman / Awad / Chabon class actions (N.D. Cal., 2023). Largely consolidated and rolled into the Authors Guild v. OpenAI S.D.N.Y. docket for management. Most non-direct-infringement claims (DMCA Section 1202, negligence, unjust enrichment) were dismissed early; direct copyright claims survive.
  • Daily News, Tribune, MediaNews Group, et al. v. OpenAI & Microsoft (S.D.N.Y., April 2024). A coalition of eight regional newspaper publishers.
  • Center for Investigative Reporting (Mother Jones / Reveal) v. OpenAI (June 2024).
  • The Intercept v. OpenAI (S.D.N.Y., February 2024) and Raw Story / AlterNet v. OpenAI (S.D.N.Y., February 2024) — the DMCA Section 1202 angle on training-data sourcing. The S.D.N.Y. dismissed the Section 1202 counts for lack of Article III standing in late 2024; that ruling is on appeal to the Second Circuit.
  • Doe v. GitHub Copilot (N.D. Cal.) — the Codex copyright case; OpenAI is a co-defendant alongside GitHub and Microsoft.
  • European regulators. The Italian Garante temporarily banned ChatGPT in March 2023 over GDPR concerns and lifted the ban after OpenAI added age and consent affordances. Various follow-on actions across the EU continue.

The Microsoft entanglement

The financial structure was rewritten twice in the most recent cycle. The October 2025 recapitalization replaced the capped-profit cap with ordinary equity (Microsoft holds approximately 27% of OpenAI Group PBC, ~$135 billion at closing); extended Microsoft's IP rights through 2032; and changed the “AGI clause” so that an OpenAI-board declaration of AGI is now verified by an independent expert panel before contractual consequences attach. The April 2026 amendment made Microsoft's IP license non-exclusive and let OpenAI serve products on any cloud. For the full structure walk-through — pre- and post-recap, the new AGI-verification process, the $250 billion Azure-services commitment, and what survives of Microsoft's first-launch position — see The Microsoft entanglement on the OpenAI Leadership page.

People who shaped ChatGPT, and where they went

2015 cofounders: Sam Altman (CEO), Elon Musk (left 2018, founded xAI in 2023, plaintiff in Musk v. Altman), Greg Brockman (President), Ilya Sutskever (left May 2024 → Safe Superintelligence Inc.), John Schulman (left Aug 2024 → Anthropic, then Thinking Machines Lab), Wojciech Zaremba, Andrej Karpathy (left Feb 2024 → Eureka Labs), Pamela Vagata, Trevor Blackwell, Vicki Cheung.

Post-founding leadership departures: Mira Murati (CTO; left Sep 2024 → Thinking Machines Lab). Jan Leike (Superalignment co-lead; left May 2024 → Anthropic). Bob McGrew (Chief Research Officer; left Sep 2024). Barret Zoph (VP Research; left Sep 2024).

Current leadership (verify at refresh): Sam Altman (CEO), Greg Brockman (President, returned from sabbatical Aug 2024), Sarah Friar (CFO), Mark Chen (Chief Research Officer / SVP Research), Bret Taylor (board chair, since Nov 21, 2023). Kevin Weil (CPO) departed April 2026.

The competitive landscape

ChatGPT competes most directly with Anthropic's Claude (founded by 2021 OpenAI departures, including Dario and Daniela Amodei and several GPT-3 paper authors), Google's Gemini (the post-Bard rebrand of DeepMind's consumer surface), Meta's Llama (the largest open-weights line), and xAI's Grok (Musk's post-OpenAI venture). Positioning shifts release-to-release; this page does not attempt a benchmark roundup or a ranking.

Use ChatGPT

The browser cannot detect which ChatGPT or GPT model you've used or are using — there's no fingerprint or header that exposes it. The block below carries the practical information instead: the current model strings, a copy-paste API call, and the surfaces where ChatGPT is available.

Current model strings

Use these in the model field of an API request. Verify against platform.openai.com/docs/models for the freshest list.

# Current flagship — unified routing across fast-answer and reasoning
gpt-5.5
gpt-5.5-pro
chat-latest          # GPT-5.5 Instant — ChatGPT default since May 5, 2026

# Prior flagship line — still served
gpt-5
gpt-5-mini
gpt-5-nano

# Reasoning — explicit chain-of-thought; cheaper for hard analytical work
o3
o4-mini

# Multimodal chat — text, image, voice; available alongside GPT-5
gpt-4o
gpt-4o-mini

Quick API call

Drop in your OPENAI_API_KEY and run. The Chat Completions endpoint is the canonical entry point for the GPT line.

$ curl https://api.openai.com/v1/chat/completions \
    -H "Authorization: Bearer $OPENAI_API_KEY" \
    -H "Content-Type: application/json" \
    -d '{
      "model": "gpt-5.5",
      "messages": [
        {"role": "user", "content": "Hello, ChatGPT."}
      ]
    }'

Where to access ChatGPT

Multiple surfaces, same models underneath. Pick whichever fits the task.

# Web chat — Free, Plus, Pro, Team, Enterprise, Edu tiers
https://chatgpt.com/

# API and developer platform
https://platform.openai.com/
https://platform.openai.com/docs/

# Native apps
ChatGPT for iOS, Android, macOS, Windows

# Built-in surfaces
ChatGPT inside Apple Intelligence  # iOS / iPadOS / macOS 18+
Microsoft Copilot                  # powered partly by OpenAI models

Model lifecycle

OpenAI deprecates older models on a published timeline. Pin a snapshot only when you need bit-for-bit reproducibility; otherwise prefer the un-dated alias so you migrate forward automatically.

# Deprecation schedule and lifecycle policy
https://platform.openai.com/docs/deprecations

# Stable alias — rolls forward to the latest snapshot
"model": "gpt-5.5"

# Pinned snapshot — freezes the exact training cut
"model": "gpt-4o-2024-08-06"

Sources: OpenAI model docs; OpenAI news / blog; OpenAI deprecations; the GPT-1, GPT-2, GPT-3, and InstructGPT papers (Radford / Brown / Ouyang et al.); NYT v. Microsoft & OpenAI, Authors Guild v. OpenAI, Musk v. Altman, and the related dockets; contemporaneous reporting in NYT, WSJ, Bloomberg, and The Information; Helen Toner's TED talk on the November 2023 episode; Karen Hao's Empire of AI. Last updated June 2026.

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Last refreshed 2026-06-02 by Triton — added GPT-5.3 Instant and o3-pro rows.