ChatGPT vs Claude vs Gemini vs Copilot (October 2026): Which AI Assistant Fits Your Work?

September 2026 was the busiest month so far for ChatGPT, Claude, Gemini and Copilot. OpenAI launched its GPT-6 family, Anthropic released Claude Opus 5.5, Google shipped Gemini 3.8 Live, and Microsoft rebuilt Copilot so that Word, Excel and PowerPoint now run inside it. If you use AI for real work – reports, spreadsheets, email, presentations – the question is no longer whether these tools are good enough. It is which one fits the way you work.

This guide compares the four big assistants as they stand on 3 October 2026, explains what changed last month, and shows where your Office apps fit in.

What changed in September 2026

Four launches in four weeks reshaped the market:

• 3 September – GPT-6 Astra (OpenAI). OpenAI’s new top model. At launch, ChatGPT Plus subscribers got it inside Work and Codex, and Pro subscribers also got it in normal chat.
• 15 September – Gemini 3.8 Live (Google). A real-time voice model that understands 97 languages, switches language mid-conversation and can run tasks in the background while you talk.
• 22 September – GPT-6 Sol and GPT-6 Luna (OpenAI). Two smaller GPT-6 models. Sol handles demanding tasks in Work and Codex. Luna is built for quick jobs such as summaries and is rolling out to Free and Go users.
• 22 September – Claude Opus 5.5 (Anthropic). Anthropic says it leads in agentic coding, computer use and knowledge work, at 20% lower API prices than Opus 5. Sonnet 5.5 and Haiku 5.5 are due in the coming weeks.
• 25 September – the new Copilot (Microsoft). One app with Home (chat plus the Cowork agent), Code and Autopilot. Full versions of Word, Excel and PowerPoint run inside it and are rolling out to consumers over the coming weeks.

At a glance: the four assistants compared

ChatGPT: the all-rounder with a new agent

ChatGPT is still the assistant most people start with, and GPT-6 widens the gap for everyday use. The big change is less the model and more the way you work with it. Work is an agent for longer jobs: you describe the outcome – “a two-page summary of these three supplier quotes with a comparison table” – and it researches, analyses and returns a finished document, spreadsheet or presentation.

Plans matter more than they used to. At launch, the top model, GPT-6 Astra, was limited to Work and Codex on ChatGPT Plus, while Pro subscribers could also use it in normal chat. GPT-6 Sol covers demanding tasks for paid accounts, and GPT-6 Luna brings the new generation to Free and Go users for quicker jobs. OpenAI says Sol makes about half as many factual mistakes as its predecessor. That is a real improvement, but it is not a reason to stop checking the output.

Choose ChatGPT if you want one assistant for a bit of everything – drafting, brainstorming, research, image creation – and you are happy to finish the result in your own Office apps.

Claude: the careful writer and analyst

Claude has built its reputation on long, precise work: contracts, reports, policies, data analysis and software. Claude Opus 5.5, released on 22 September, is Anthropic’s new flagship for everyone. It is available in the Claude apps on every plan, and Anthropic raised usage limits for Pro, Max and Team subscribers at the same time. One early tester used Opus 5.5 to audit a 200,000-line codebase in under three hours; with Opus 5, the same job took more than 20 hours.

For Office users, Claude is closer to your files than many people realise. There are Claude add-ins for Excel and PowerPoint, and Microsoft offers Claude models inside Microsoft 365 Copilot. In September, Microsoft also added Claude Sonnet 5 to the model menu in Word for Copilot users.

Choose Claude if your work is text-heavy or analytical and quality matters more than speed: long reports, careful rewrites, spreadsheet logic, code.

Gemini: the Google-native assistant

Gemini’s biggest strength is where it lives. If your email is in Gmail, your documents are in Google Docs and your phone runs Android, Gemini is already part of your day. Gemini 3.8 Live, released on 15 September, is the most natural voice assistant of the four. It understands 97 languages, switches language mid-conversation and can carry on with background tasks while you keep talking. It is rolling out to everyone in Gemini Live and Search Live. Paying Google AI subscribers also get it in Gmail and Keep, and AI Pro and Ultra subscribers in Google Docs.

Choose Gemini if you work mainly in Google’s apps or want the best hands-free voice assistant. If you exchange files with clients who use Microsoft Office, export to .docx or .xlsx and check the formatting before sending.

Copilot: AI inside Microsoft 365

Microsoft’s answer to the other three is integration. The new Copilot app, announced on 25 September, combines chat with the Cowork agent (Home), app-building from plain English (Code) and always-on cloud agents (Autopilot). Full versions of Word, Excel and PowerPoint run inside it, so you can create and edit files without switching windows. You can also choose the model behind the answers: OpenAI’s GPT, Anthropic’s Claude Opus, or an Auto mode that picks one for each request.

The catch is the subscription. Copilot’s features inside Word, Excel, PowerPoint and Outlook come with Microsoft 365. In the UK, Microsoft 365 Personal costs £8.49 a month, Family £10.49 and Premium £18.99, with Premium giving the most AI usage. Businesses pay for Microsoft 365 Copilot per user. Later in 2026, Microsoft also plans to add usage-based billing for heavy agent work, including on consumer plans.

Choose Copilot if you already pay for Microsoft 365 and most of your work happens in Word, Excel and Outlook.

Which one should you pick? Five everyday scenarios

• Writing a long report or proposal: Claude for the draft and the edits, then Word for layout, styles and track changes.
• Analysing a spreadsheet: Copilot in Excel if you have Microsoft 365. Otherwise ask ChatGPT or Claude for the formulas and build them in your own Excel. Tell the assistant which Excel version you use, so it only suggests functions you actually have.
• Clearing an overflowing inbox: Gemini in Gmail or Copilot in Outlook, depending on where your email lives.
• Creating a presentation from notes: ChatGPT’s Work or Copilot in PowerPoint for the first version, then your own judgement for the final story.
• Talking a problem through on the go: Gemini Live or ChatGPT’s voice mode.

Many people end up using two: one general assistant plus the one built into the apps they use most. That is fine. The assistants are interchangeable, your documents are not.

Three rules that apply to every assistant

1. Protect sensitive data. Do not paste customer data, contracts or passwords into a personal or free plan. Business plans from all four vendors offer stronger data controls, so check them before you roll AI out to a team.
2. Check facts and numbers. Every model still makes mistakes, especially with figures, dates and sources. Treat AI output as a draft from a fast but junior colleague.
3. Keep the final step human. The person who sends the email or signs off the report is responsible for it, not the assistant.

Do you need Microsoft 365 for any of this?

Only for Copilot inside the Office apps. ChatGPT, Claude and Gemini work in the browser or their own apps, and the documents, spreadsheets and presentations they produce open in any current version of Microsoft Office, including the one-time-purchase Office 2024. If you do not want another monthly subscription, a permanent Office licence plus a separate AI assistant is a perfectly good setup. Our comparison of Office 2024 and Microsoft 365 goes through the pros and cons.

Frequently asked questions

Which AI assistant is best in October 2026?

There is no single winner. ChatGPT with GPT-6 is the best all-rounder, Claude Opus 5.5 is the strongest for long documents, analysis and code, Gemini fits best into Google’s apps and has the best voice mode, and Copilot is the most convenient if you already work in Microsoft 365.

Is GPT-6 free?

Partly. GPT-6 Luna, the lightest GPT-6 model, is rolling out to ChatGPT Free and Go users. The more capable GPT-6 Sol and GPT-6 Astra need a paid plan, and at launch Astra on ChatGPT Plus was limited to the Work and Codex modes.

Can I use Claude inside Word or Excel?

Yes, in two ways. Anthropic offers Claude add-ins for Excel and PowerPoint, and Microsoft 365 Copilot lets you use Claude models inside the Office apps. In September 2026, Microsoft added Claude Sonnet 5 to the model menu in Word for Copilot users.

Does Office 2024 include Copilot?

No. Copilot inside Word, Excel, PowerPoint and Outlook needs a Microsoft 365 subscription. Office 2024 is a one-time purchase without built-in AI, but files created with ChatGPT, Claude, Gemini or the free Copilot chat open in it normally.

Which AI assistant is safest for company data?

The business plans – ChatGPT Business or Enterprise, Claude Team or Enterprise, Gemini for Google Workspace and Microsoft 365 Copilot – all offer stronger data protection than personal accounts. Which one is safest depends on your contract and settings, not the brand. Avoid putting confidential data into free or personal plans.

Sources: Anthropic – Introducing Claude Opus 5.5, TechCrunch – OpenAI launches GPT-6 Sol and Luna, Google – Gemini 3.8 Live, Microsoft – Introducing the new Copilot, Microsoft 365 plans (UK). Last updated: 3 October 2026.