OpenAI Sets ChatGPT Retirement Dates for o3 and GPT-4.5

OpenAI added a Retiring OpenAI o3 and GPT-4.5 entry to its ChatGPT release notes on May 28, 2026. The dates are short and specific. GPT-4.5 gets a 30-day sunset and retires from ChatGPT on June 27, 2026. OpenAI o3 gets a 90-day sunset and retires from ChatGPT on August 26, 2026. OpenAI says both models are currently available only to paid users through model settings.

The line developers should read first is the scope note. OpenAI states that these changes apply only to ChatGPT and that there are no API changes. Even when the same model name appears in both places, the ChatGPT product model picker and OpenAI API model endpoints do not necessarily share the same lifecycle. This is not a notice that the o3 API disappears immediately. It is a notice that legacy choices people select manually inside ChatGPT are being removed.

The schedule fits a broader May product cleanup in ChatGPT. OpenAI says it shipped GPT-5.5 Instant as the ChatGPT default model on May 5, 2026, then posted response-style and quality updates for GPT-5.5 Instant and the API on May 28. The same release-note cluster says canvas is no longer available in GPT-5.5 Instant and GPT-5.5 Thinking, while paid users can keep using canvas with legacy models until those models are sunset.

At the product surface, OpenAI is signaling that it does not want to keep old and new default experiences side by side for long. The May 5 note says paid users can access GPT-5.3 Instant in model configuration settings for three more months. The May 28 GPT-4.5 30-day and o3 90-day windows follow the same pattern. ChatGPT pushes the newest default model forward, moves older models deeper into settings, then removes them on a dated sunset schedule.

The API documentation tells a different story. OpenAI Developers already labels GPT-4.5 Preview as Deprecated. That page describes it as a deprecated large model and recommends gpt-4.1 or o3 for most use cases. Pricing is another signal: the page lists GPT-4.5 Preview at $75 per million input tokens and $150 per million output tokens.

The o3 API page still reads like an active model document. OpenAI describes o3 as a reasoning model for complex tasks, with strengths in math, science, coding, visual reasoning, technical writing, and instruction following. The same page also says GPT-5 is its successor. According to the model card cited in the Korean research note, o3 provides a 200,000-token context window and up to 100,000 output tokens.

That split is the operational point. ChatGPT users will no longer be able to choose these models from the product UI after June 27 and August 26. API users do not see an endpoint shutoff from this specific notice. But once GPT-4.5 Preview is already deprecated and o3 has a named successor, production systems should not treat model aliases or snapshots as permanent infrastructure.

GPT-4.5 always had an ambiguous position in OpenAI's model lineup. In OpenAI's February 27, 2025 Introducing GPT-4.5 post, the benchmark table listed GPT-4.5 at 71.4% on GPQA, 85.1% on MMMLU, and 74.4% on MMMU. In the same table, o3-mini high posted 87.3% on AIME 2024 and 61.0% on SWE-Bench Verified, showing a different profile around reasoning and coding. OpenAI also cautioned at the time that academic benchmarks do not fully capture real usefulness.

For development teams, that difference in behavior is more practical than the leaderboard framing. Many teams use ChatGPT by switching models for document drafts, code-review comments, evaluation prompts, and long analysis. They send the same prompt to GPT-4.5, o3, and newer GPT-5.5 variants to compare tone, reasoning depth, hallucination patterns, and cost expectations. When the UI choices disappear, that informal evaluation workflow changes too.

The ChatGPT retirement schedule is also worth comparing with OpenAI's longer API deprecation rhythm. The API deprecations page described legacy GPT model snapshot retirement in September 2025 and cited lower usage and model-choice simplification as reasons for ending older models after a six-to-twelve-month transition period. Examples in that page included gpt-4-0314, gpt-4-1106-preview, and gpt-4-0125-preview, with shutdown dates set for March 26, 2026.

The ChatGPT model picker is more visible to users than API snapshots. In an API integration, teams can inspect logs and evals to see when behavior changes. In ChatGPT, individuals and teams mix conversation history, custom instructions, uploaded files, connected apps, and model-choice habits. A 30-day sunset can feel less like a menu cleanup and more like an expiration date for an accumulated way of working.

TechRadar framed the May 29, 2026 news as the quiet disappearance of the last GPT-4-family model from ChatGPT. Reddit posts in r/ChatGPTcomplaints included users calling o3 and GPT-4.5 the last models they genuinely preferred. That reaction is emotional and not a product metric, but it exposes a product-management issue. Users treat model names not just as capability labels, but as anchors for memory, workflow, and expected output style.

OpenAI also has reasons to retire legacy model choices. A crowded model picker makes it harder for users to know what to choose. Each model adds safety, latency, cost, feature-compatibility, and support burden. The May 28 note's canvas change belongs in that same category. Newer model families are absorbing writing and coding blocks inside the chat response, while legacy models remain on an exception path until their sunset dates.

AI product teams can turn this notice into three concrete tasks. First, if GPT-4.5 defines an output bar for a workflow, save representative prompts and outputs before June 27, 2026. Second, if o3 is the team's reasoning baseline, run comparisons before August 26 against GPT-5.5 Thinking, API o3, or the relevant GPT-5 family models. Third, track ChatGPT product notices and API deprecation calendars as separate systems rather than assuming one implies the other.

The phrase "no changes to the API" is not a permanent waiver. It means endpoints are not closing because of this ChatGPT notice. It does not mean the model-selection policy is fixed indefinitely. GPT-4.5 Preview is already marked deprecated in API docs, and OpenAI has previously used declining usage as part of its deprecation rationale. Any production system with hardcoded model names should have fallback routing, eval thresholds, and a documented replacement path.

Internal team documentation deserves the same treatment. If a process says "review this in ChatGPT with o3" or "match the tone with GPT-4.5," that procedure now has a dated dependency. After late June, one instruction stops being reproducible. After late August, the other does too. AI operating docs should specify the product surface, the model, the replacement candidate, the applicable date, and the last time the team validated the workflow.

This is less a model leaderboard story than a model lifecycle story. OpenAI is simplifying ChatGPT around newer defaults while using separate developer documentation for API deprecations and snapshots. The practical question for AI builders is whether their prompts, review standards, and eval habits are tied to a product UI that can change on a 30-day schedule. June 27 and August 26 are not just two retirement dates in ChatGPT; they are deadlines for checking whether informal model-dependent workflows have been captured in a form the team can reproduce.