When does GPT-4.5 retire and what happens to my chats?

GPT-4.5 retires from ChatGPT on June 27, 2026, following a 30-day sunset period that started in late May. ChatGPT users on plans that defaulted to GPT-4.5 will be automatically migrated to GPT-5 (and in practice GPT-5.5, which became the default on June 12, 2026). Existing chats remain accessible — they just won't run on GPT-4.5 after June 27. Note: GPT-4.5 was already removed from the OpenAI API last year, so this June 2026 retirement is the consumer-side completion of that earlier deprecation. There is no API migration required at this point — if you're still calling GPT-4.5 via the API, your calls have been failing for months.

What model should I migrate to from GPT-4.5?

For ChatGPT users, the automatic migration target is GPT-5 — and in practice GPT-5.5, which has been the ChatGPT default since June 12, 2026 after OpenAI retired older GPT-5.2 models. For API users (if you somehow still have GPT-4.5 API integrations, which is unlikely since it was deprecated last year), migrate to gpt-5 or gpt-5.5 depending on use case. GPT-5.5 Instant is faster but produces shorter, less-structured outputs as of OpenAI's June 3, 2026 behavior change. For longer-form reasoning, use gpt-5 standard or wait for GPT-5.6 (Polymarket window suggests Q3 2026). The OpenAI o3 model is also retiring on August 26, 2026 after a 90-day sunset period.

Will my custom GPTs or saved prompts break?

Custom GPTs and saved prompts will continue to work — they're configuration, not model bindings. They will run on whatever your default model is at query time, which is now GPT-5.5. However, prompts that were carefully tuned for GPT-4.5's specific verbosity, structure, or tone may need light touch-up. Specifically: (1) GPT-5.5 Instant produces shorter, less-structured outputs than GPT-4.5 did. If your custom GPT expects long structured Markdown answers, consider switching to gpt-5 standard or adding explicit format instructions. (2) Tool-use behavior has changed — GPT-5.5 is more conservative about tool calls. If your custom GPT uses actions/tools, test before the cutover.

What's the timeline for other OpenAI model retirements in 2026?

Two more retirements on the calendar as of June 2026: (1) GPT-4.5 from ChatGPT — June 27, 2026, with the 30-day sunset already underway. (2) OpenAI o3 from ChatGPT — August 26, 2026, with a 90-day sunset period. The o3 retirement is particularly notable because o3 was a popular reasoning model; ChatGPT users who default to o3 should plan migration to GPT-5.5 standard or wait for GPT-5.6. On the API side, OpenAI also retired Realtime API v1 (Beta) on May 12, 2026 and is migrating the Assistants API to the Responses API and Conversations API before its 2026 shutdown. If you have hardcoded API integrations on legacy endpoints, audit them this quarter.

Quick Answer

How to Migrate from GPT-4.5 Before June 27 2026 Retirement

Published: June 20, 2026

How to Migrate from GPT-4.5 Before June 27 2026 Retirement

OpenAI retires GPT-4.5 from ChatGPT on June 27, 2026. The 30-day sunset period is already underway. ChatGPT users auto-migrate to GPT-5 (in practice GPT-5.5, the default since June 12). API users already migrated last year. Here is the full migration checklist.

Last verified: June 20, 2026. Retirement date: June 27, 2026. OpenAI release notes confirm 30-day sunset.

TL;DR

What’s retiring: GPT-4.5 from ChatGPT.
When: June 27, 2026.
What replaces it: GPT-5.5 (the ChatGPT default since June 12, 2026 when older GPT-5.2 models were retired).
ChatGPT users: Auto-migration. No action required.
API users: GPT-4.5 was already deprecated from the API last year. If you have it hardcoded, calls have been failing for months.
Custom GPTs: Continue to work. Test for behavior changes — GPT-5.5 Instant is shorter and less structured.
Also retiring: OpenAI o3 from ChatGPT on August 26, 2026 (90-day sunset).

The retirement timeline

Date	Event
2025	GPT-4.5 deprecated from OpenAI API
May 12, 2026	OpenAI-Beta: realtime=v1 (Realtime API) retired
May 28, 2026 (~30-day sunset start)	GPT-4.5 sunset announced for ChatGPT
June 3, 2026	GPT-5.5 Instant behavior changed: shorter, less-structured outputs
June 12, 2026	OpenAI retired older GPT-5.2 models. GPT-5.5 becomes the new default
June 27, 2026	GPT-4.5 retired from ChatGPT
August 26, 2026	OpenAI o3 retired from ChatGPT (90-day sunset)
2026 (TBD)	Assistants API shutdown — migrate to Responses API + Conversations API

Step 1: Confirm what you’re actually using

Check your ChatGPT model picker. If GPT-4.5 appears as a selectable option, you’re still in the affected cohort. ChatGPT Plus, Team, Pro, and Enterprise plans may have had different default model exposures during the GPT-5 rollout — verify in your account settings.

For API users:

# Check whether any of your code still references GPT-4.5
grep -r "gpt-4.5" --include="*.py" --include="*.js" --include="*.ts" .

If this returns matches, your code has been failing since the API deprecation last year. Fix it before any new deployment.

Step 2: Choose your migration target

For most use cases:

Use case	Migrate to
General ChatGPT use	GPT-5.5 (automatic)
Long reasoning / structured outputs	gpt-5 standard (not Instant)
Coding	gpt-5 or wait for GPT-5.6
Fast cheap calls	gpt-5.5 Instant — but expect shorter outputs
Tool use / agent workflows	gpt-5 — more conservative tool calls than GPT-4.5
Reasoning-heavy (former o3 use)	gpt-5 standard now; plan for o3 retirement Aug 26

Step 3: Test for behavior changes

Three behavior changes to watch for during migration:

GPT-5.5 Instant is shorter and less structured. This is intentional (OpenAI’s June 3, 2026 change). If your prompts expected long Markdown, add explicit format instructions or switch to gpt-5 standard.
Tool use is more conservative. GPT-5.5 doesn’t fire tools as eagerly as GPT-4.5 did. Custom GPTs with actions/tools should be tested for missed calls.
Tone shifts. GPT-5.5 is slightly more direct and less verbose than GPT-4.5. Brand voice prompts may need tuning.

Test checklist

Run your 10 most common prompts on GPT-5.5 and compare to GPT-4.5 baseline outputs.
Test custom GPTs end-to-end including any actions/tools.
Verify saved prompts produce acceptable outputs.
Check word-count expectations — GPT-5.5 Instant is shorter.
Check JSON/structured-output prompts — GPT-5.5 still emits them but with different formatting tendencies.

Step 4: Update documentation and team guidance

If your team has internal docs, README files, or AI usage policies that reference GPT-4.5:

Update model references from gpt-4.5 to gpt-5.5 (or gpt-5 for reasoning use).
Update screenshots and tutorials.
Update API code samples to current model names.
Add a note about the June 27 retirement so team members understand why prompts may behave differently.

Step 5: Plan for the August 26 o3 retirement

This is the next shoe to drop. OpenAI o3 retires August 26, 2026 with a 90-day sunset. If your team uses o3 for reasoning-heavy work, the migration target is:

gpt-5 standard for general reasoning.
gpt-5.6 if available before August 26 (Polymarket window suggests Q3 2026 release).

The o3 retirement is more consequential than GPT-4.5 because o3 is a reasoning model with specific strengths (long-chain reasoning, math, agentic planning) that gpt-5 standard partially replaces but not 1:1.

Step 6: Audit your API surface for other deprecations

Beyond GPT-4.5, OpenAI is consolidating its API:

Realtime API v1 (Beta): retired May 12, 2026. Migrate to current Realtime API.
Assistants API: scheduled shutdown in 2026. Migrate to Responses API + Conversations API.
Older embedding models: check OpenAI’s API deprecation page for current status.

This is a good moment to do a full API surface audit. If you have any hardcoded model names, migrate them to version-pinned current models or use the OpenAI “alias” endpoints for future-proofing.

Step 7: Don’t panic about price changes

GPT-5.5 pricing for API users is in line with GPT-4o tier and lower than GPT-5 standard. For ChatGPT plan users, the migration is automatic at no additional cost. The economic story is “more capability for the same money.”

What this means for the broader AI tooling stack

Tools that wrap OpenAI’s API — Cursor, Windsurf, Claude Code, Lovable, Bolt, Replit Agent — handle model migration on their own release cadence. You generally don’t need to do anything here; the wrappers track model versions and update defaults. Watch for tool-specific release notes in late June 2026 confirming their GPT-4.5 cutover.

If you build your own OpenAI integration: this is a periodic reminder that model names are not stable infrastructure. Build for migration: pin versions, abstract behind a model-router, and budget time each quarter for model audits.

Sources

OpenAI Help Center: “ChatGPT — Release Notes” (June 2026)
OpenAI Releasebot: “OpenAI Release Notes — June 2026 Latest Updates”
ChatForest: “OpenAI’s June 3 Update: GPT-5.5 Instant Behavior Changed and Two Models Get Retirement Dates”
TheGPUTrade: “OpenAI retires GPT-4.5 and o3 as IPO talk heats up”
Witho2: “OpenAI Kills GPT-4.5 on June 27 — Migration Guide for API Users”

Published June 20, 2026 by andrew.ooo. See related coverage: GPT-5.6 release window and Claude Fable 5 paywall.