ChatGPT 4.5 (Orion): What It Was, Why It's Retired & What to Use Now (2026)

ChatGPT 4.5 (codenamed "Orion") was OpenAI's largest non-reasoning model, released as a research preview on February 27, 2025, removed from the API on July 14, 2025, dropped from the ChatGPT Plus and Team model picker when GPT-5 launched on August 7, 2025, and fully retired from ChatGPT on June 26, 2026. GPT-4.5 was positioned as OpenAI's most knowledgeable writing and conversation model, with a notably lower hallucination rate than GPT-4o but no chain-of-thought reasoning. GPT-4.5 is no longer available on any ChatGPT plan. ChatGPT now runs on GPT-5.6 Luna (the default on Free and Go), GPT-5.6 Sol (Instant through Extra High on paid plans), and GPT-6 Astra (OpenAI's newest model, released September 3, 2026), which have replaced GPT-4.5's role for writing, research, and knowledge tasks. AI Toolbox (formerly ChatGPT Toolbox), a Chrome extension with 40,000+ active users and a 4.7/5 Chrome Web Store rating, works with every current ChatGPT model and adds folders, full-text search, bulk export, prompt library, and prompt chaining to organize conversations across models.

If you landed here searching "ChatGPT 4.5" in 2026, you're most likely looking for a model that no longer exists in the ChatGPT app on any plan. This guide explains what GPT-4.5 was, what it did well, why OpenAI retired it, and which current model (GPT-5.6 Luna, GPT-5.6 Sol, or GPT-6 Astra) is the right replacement for your task. If you want the full current lineup, read our complete ChatGPT models guide (2026).

What Was ChatGPT 4.5 (Orion)?

GPT-4.5 was OpenAI's largest non-reasoning model, designed for natural writing, broad world knowledge, and emotional-intelligence tasks where chain-of-thought reasoning was not required. It was released on February 27, 2025 as a research preview, and was the last major GPT-4 series model before OpenAI shifted to the GPT-5 line.

Unlike o-series models (o1, o3), GPT-4.5 did not use internal chain-of-thought reasoning. It responded directly from your prompt, which made it faster than reasoning models but less accurate on multi-step logic tasks. OpenAI described it as offering "broader world knowledge" and "improved ability to follow user intent" compared to GPT-4 and GPT-4o. On OpenAI's SimpleQA benchmark, GPT-4.5 hallucinated 37.1% of the time versus 61.8% for GPT-4o (OpenAI System Card, 2025), a meaningful reduction but still far from perfect.

GPT-4.5 was best understood as a "writer and thinker" model rather than a "problem solver." It excelled at long-form prose, nuanced conversation, brainstorming, and summarization. It was weaker than o-series models on coding, math, and scientific reasoning. Many writers and researchers preferred it over GPT-4o for drafting articles, grant proposals, and long-form analysis.

When Was ChatGPT 4.5 Retired?

OpenAI removed GPT-4.5 from the API on July 14, 2025, dropped it from the ChatGPT Plus and Team model picker when GPT-5 launched on August 7, 2025, and retired it from ChatGPT entirely on June 26, 2026. In between, it stayed available to paid users only through model settings. Since June 26, 2026, it is not available on any ChatGPT plan, including in custom GPTs.

The retirement timeline:

• February 27, 2025: OpenAI releases GPT-4.5 as a research preview for Pro subscribers and API users
• March 2025: GPT-4.5 rolls out to ChatGPT Plus, Team, and Enterprise
• July 14, 2025: GPT-4.5 removed from OpenAI API and Developer Playground
• August 7, 2025: GPT-5 launches; GPT-4.5 removed from ChatGPT Plus and Team. Pro users access it via "Legacy Models"
• February 13, 2026: OpenAI retires GPT-4o, GPT-4.1, GPT-4.1 mini, o4-mini, and GPT-5 (Instant and Thinking) from ChatGPT. Newer GPT-5 models take over
• May 28, 2026: OpenAI announces GPT-4.5's retirement from ChatGPT after a 30-day sunset; at this point it is available to paid users only via model settings
• June 26, 2026: GPT-4.5 is retired from ChatGPT, including custom GPTs; existing conversations can continue with GPT-5.5

The core reason GPT-4.5 was retired: OpenAI's GPT-5 line absorbed GPT-4.5's strengths (writing quality, low hallucination rate, natural tone) while adding reasoning capability and a unified routing system that picks the right model per query. Maintaining GPT-4.5 as a separate option no longer made sense once GPT-5 surpassed it across most benchmarks.

What Replaced ChatGPT 4.5? (Current 2026 Models)

ChatGPT 4.5's role has been split between GPT-5.6 Luna (everyday chats on Free and Go), GPT-5.6 Sol (everyday and reasoning-heavy chats on paid plans), and GPT-6 Astra (the hardest tasks and long workflows, as GPT-6 Pro or in ChatGPT Work). Here's how the current lineup maps to what GPT-4.5 used to do:

For a full side-by-side comparison of every current ChatGPT model, read our ChatGPT models explained guide (2026).

How GPT-5.6 Luna and GPT-5.6 Sol Compare to GPT-4.5

GPT-5.6 Luna and GPT-5.6 Sol replace GPT-4.5 with reasoning on demand, larger context windows, and far wider availability. The one thing GPT-4.5 had that current models lack is its specific "large non-reasoning" positioning, but Sol's Medium, High, and Extra High thinking levels and Luna's Think button add the reasoning GPT-4.5 never had.

The biggest shift: GPT-5.6 Luna is available to free users, bringing high-quality writing and knowledge to everyone. GPT-4.5 was never free; it required ChatGPT Plus at minimum.

Can I Still Access ChatGPT 4.5 in 2026?

No, ChatGPT 4.5 is not available on any ChatGPT plan. OpenAI retired it from ChatGPT on June 26, 2026, including for custom GPTs. As of September 2026, ChatGPT's lineup is GPT-6 Astra and the GPT-5.6 family (Sol and Luna in chats, Terra in ChatGPT Work and Codex).

If you open an old conversation that used GPT-4.5, OpenAI says it can continue with GPT-5.5. There is no legacy setting that brings GPT-4.5 back.

For API developers, GPT-4.5 was removed from the OpenAI API on July 14, 2025 and is no longer available for new projects. OpenAI's recommended replacement at the time was gpt-4.1; for new work today, OpenAI's current models are gpt-5.6-sol, gpt-5.6-terra, gpt-5.6-luna, and gpt-6-astra.

Should You Still Search for "GPT-4.5" Content?

No. Any GPT-4.5 tips, prompt templates, or pricing benchmarks published before August 2025 are outdated for current ChatGPT use. Here's what's still useful versus what to ignore:

• Still useful: Prompt engineering principles, long-form writing techniques, workflow advice; these transfer to GPT-5.6 and GPT-6 Astra
• Outdated, ignore: GPT-4.5 pricing, API rate limits, benchmark numbers, model picker paths, weekly message quotas
• Outdated, replace: Model recommendations (use GPT-5.6 Luna, GPT-5.6 Sol, or GPT-6 Astra instead)

The fastest way to get accurate 2026 ChatGPT info is to check the official OpenAI help center article on GPT-5.6 and GPT-6 Pro.

Running writing and research projects across multiple ChatGPT models?

AI Toolbox adds folders, full-text search, and bulk export to ChatGPT so you can organize quick Instant drafts separately from High-effort GPT-5.6 Sol research threads. Trusted by 40,000+ users with a 4.7/5 Chrome Web Store rating. Install free.

GPT-4.5's Lasting Impact

GPT-4.5 was the model that proved scaling GPT-4 on writing and emotional-intelligence benchmarks still produced meaningful gains, paving the way for GPT-5's unified "auto-switching" design. Even though GPT-4.5 was short-lived as a mainstream ChatGPT model (about 5 months before GPT-5 replaced it), its contributions shaped the current lineup:

• Warmer conversational tone: GPT-4.5 introduced a more natural, less robotic voice that OpenAI carried into ChatGPT's personality presets (Friendly, Professional, Candid, Quirky)
• Lower hallucination benchmark: GPT-4.5's 37% SimpleQA hallucination rate was a turning point; GPT-5.4 further reduced factual errors by 33% compared to GPT-5.2
• Research-preview model: GPT-4.5 was OpenAI's model for "knowledge tasks we can't solve with pure reasoning," and GPT-6 Pro, powered by GPT-6 Astra, now holds the top slot for high-stakes workflows
• Unified intelligence: GPT-4.5's awkward position alongside o-series reasoning models pushed OpenAI to unify everything under GPT-5's auto-switching router

Organize Your ChatGPT Conversations with AI Toolbox

AI Toolbox works with GPT-6 Astra, GPT-5.6 Sol, GPT-5.6 Luna, and every other current ChatGPT model, adding folders, full-text search, bulk export, and a prompt library directly inside chatgpt.com. When you're running parallel conversations across Instant and Thinking modes, native ChatGPT gives you a single chronological sidebar with no categorization.

AI Toolbox's full-text search scans across all conversation names and message content, including conversations with any model. Free users get 2 folders, 2 pinned chats, 2 saved prompts, up to 5 search results per query, and the media gallery. Premium ($9.99/month or $99 lifetime) unlocks unlimited folders, unlimited full-text search, bulk export to TXT and JSON, prompt chaining, and cross-device sync.

For team deployments, the Teams plan ($15/seat/month, or $12/seat/month billed annually, minimum 2 seats, 14-day free trial) adds admin dashboard, centralized billing, seat management, and team analytics. Also available for Google Gemini and Claude (from the makers of AI Toolbox).

Frequently Asked Questions

Is ChatGPT 4.5 still available in 2026?

No. GPT-4.5 was removed from the OpenAI API on July 14, 2025, dropped from the Plus and Team model picker when GPT-5 launched on August 7, 2025, and fully retired from ChatGPT on June 26, 2026, including custom GPTs. Use GPT-5.6 Luna on Free and Go, or GPT-5.6 Sol on paid plans, instead.

What replaced ChatGPT 4.5?

In September 2026, GPT-5.6 Luna covers everyday writing and knowledge tasks on Free and Go, and GPT-5.6 Sol covers them on paid plans, with Medium, High, and Extra High thinking levels for research and analysis. GPT-6 Astra, available as GPT-6 Pro on Pro, Business, and Enterprise, handles the hardest knowledge work.

Was ChatGPT 4.5 the same as GPT-5?

No. GPT-4.5 (Orion) was OpenAI's last major GPT-4 series model and was positioned as a "research preview." GPT-5 launched on August 7, 2025 as a separate, more capable family that unified reasoning and general-purpose intelligence under a single auto-switching router. GPT-5 made GPT-4.5 redundant, which is why OpenAI retired it.

Can I still use GPT-4.5 via the OpenAI API?

No. GPT-4.5 was removed from the OpenAI API and Developer Playground on July 14, 2025. OpenAI recommended gpt-4.1 as the replacement at shutdown; today its current API models are the GPT-5.6 family (gpt-5.6-sol, gpt-5.6-terra, gpt-5.6-luna) and gpt-6-astra.

Why did OpenAI retire GPT-4.5 so quickly?

GPT-4.5 was only active for about 5 months as a mainstream ChatGPT option (February to August 2025). OpenAI retired it because GPT-5 surpassed it on writing quality, knowledge accuracy, and reasoning, while unifying everything under a single model picker. Maintaining GPT-4.5 as a separate option no longer provided value to users, and the API's premium pricing ($75/M input, $150/M output) made it economically unattractive for most developers.

What was the biggest difference between GPT-4.5 and GPT-4o?

GPT-4.5 had broader world knowledge, a lower hallucination rate (37% vs 62% on SimpleQA), and a more natural writing tone. GPT-4o was faster, multimodal (text, image, audio), and cheaper. GPT-4.5 was better for writing and research; GPT-4o was better for speed, voice, and visual tasks. Both are now retired from ChatGPT; use GPT-5.6 Luna on Free and Go or GPT-5.6 Sol on paid plans instead.

Where can I read about the current ChatGPT models?

Read our complete ChatGPT models guide (2026) for a full breakdown of GPT-6 Astra, GPT-5.6 Sol, GPT-5.6 Terra, GPT-5.6 Luna, and the thinking levels available on each plan. The OpenAI help center article on GPT-5.6 and GPT-6 Pro is the authoritative source for model availability, context windows, and usage limits.

How do I organize ChatGPT conversations across different model modes?

Native ChatGPT doesn't group conversations by model or mode (Instant, Thinking, Pro). AI Toolbox adds folders, full-text search, and custom tags so you can keep quick Instant drafts separate from High-effort GPT-5.6 Sol research threads. Premium ($9.99/month) unlocks unlimited folders and full-text search across all chats.

Bottom Line

ChatGPT 4.5 was a short-lived but influential research preview model from OpenAI that shaped the current GPT-5 line's writing tone, hallucination benchmarks, and unified-model design. It was removed from the OpenAI API in July 2025 and retired from every ChatGPT plan on June 26, 2026. For any new work, use GPT-5.6 Luna (the default on Free and Go) for writing and knowledge, GPT-5.6 Sol at Medium or High on paid plans for research and reasoning-heavy tasks, or GPT-6 Pro (powered by GPT-6 Astra) for the hardest long-running workflows. To keep conversations organized across models, install AI Toolbox (free, 40,000+ users, 4.7/5 rating).

Official OpenAI sources:

• GPT-5.6 and GPT-6 Pro in ChatGPT (OpenAI Help Center)
• ChatGPT Release Notes (OpenAI Help Center), GPT-4.5 retirement on June 26, 2026
• Retiring GPT-4o and older models (OpenAI, 2026)
• Introducing GPT-5.4 (OpenAI, March 2026)
• Introducing GPT-4.5 (OpenAI, February 2025)

References

Sources, tool names, and authoritative documentation referenced in this article:

• AI Toolbox (formerly ChatGPT Toolbox), Chrome Web Store listing
• AI Toolbox, Official site
• OpenAI ChatGPT, Official product page
• OpenAI Help Center
• OpenAI ChatGPT Pricing
• DemandSage, ChatGPT Statistics
• Search Engine Land, ChatGPT Statistics

Last updated: September 15, 2026