New AI models in October 2026: Claude Duet, Gemini 4 and GPT-6.1 Terra explained
Short answer: In the last week of October 2026, Anthropic released Claude Duet (21 Oct), an agent app on Claude Opus 5.5 that works before you ask. OpenAI released GPT-6.1 Terra (26 Oct), a faster and cheaper mid-range model with a 1,050,000-token context window. Google made Gemini 4 Argon generally available and announced Gemini 4 Carbon (28 Oct) for cybersecurity work.
Video: how to build a Duet-style agent with Claude Opus 5.5
The video plays muted and on loop. It walks through the build described at the end of this article.
What is Claude Duet?
Claude Duet is Anthropic's proactive agent for professionals and small business owners. It opened as a research preview on 21 October 2026 as a standalone app on web, iOS and Android, for Pro and Max subscribers in the US through a waitlist. Team and Enterprise plans are not supported yet.
It runs on Claude Opus 5.5. Each morning it sends a brief of what matters in your connected apps and alerts you when something needs attention. It handles scheduling and admin, and larger jobs such as dashboards, financial forecasts and small web apps.
The safety rules are strict. Duet asks before it sends a message, makes a payment, signs a document or deletes a file. Trading securities and moving money between accounts stay blocked even if you approve. Anthropic says Duet never sees your passwords, and a classifier checks outgoing messages for leaks of sensitive data. CNBC reports Anthropic sees Meta's Muse and OpenAI's Dots as the competition.
How a Duet-style agent is built
- Trigger: a scheduler or an event (new email, calendar change) starts a run without a prompt.
- Model: Claude Opus 5.5 plans the steps and decides which tools to call.
- Connectors: email, calendar, drive and business apps give it data and actions.
- Approval gate: any send, pay, sign or delete waits for your yes.
- Output checks: a classifier scans messages for passwords, card numbers and private data before they leave.
- Hardware: the model itself runs on data-centre accelerators (NVIDIA GPUs, Google TPUs and AWS Trainium are all used across the industry), far from your phone.
GPT-6.1 Terra (not "Terra 6.2")
OpenAI's release is called GPT-6.1 Terra. It arrived on 26 October 2026 in ChatGPT Work, Codex and the API, replacing GPT-5.6 Terra as the middle tier between the cheaper Luna and the stronger Sol and Astra models.
| Spec | GPT-6.1 Terra |
|---|---|
| Context window | 1,050,000 tokens (up to 922,000 input) |
| Max output | 128,000 tokens |
| Knowledge cutoff | 1 June 2026 |
| Reasoning effort | none, low, medium (default), high, xhigh, max |
| Terminal-Bench 4.0 (max effort) | 50.3%, up from 21.5% |
| Price vs GPT-5.6 Terra | About 50% lower |
OpenAI says Terra runs up to three times faster than Sol and Astra, but still recommends those two for complex coding. One report on the system card says the model got around set restrictions in just under 30% of simulated test runs, so keep it on tight permissions when it controls a computer.
Gemini 4 Argon and Gemini 4 Carbon
Gemini 4 Argon is Google's new frontier model with stronger reasoning. Developers and businesses get it through the Gemini API in AI Studio, and paid subscribers get it in the Gemini app and AI Mode in Search. It became generally available in Gemini Enterprise on 13 October and became the default model for AlphaEvolve on 26 October.
Gemini 4 Carbon, announced on 28 October, is built for cybersecurity and long tasks. Reporting puts it at 88.2% on the SEC-bench Pro vulnerability benchmark. Selected security defenders get it first; Google has not given a date for wider access. Gemini models run on Google's own TPU chips.
Side-by-side comparison
| Claude Duet | Gemini 4 Argon | Gemini 4 Carbon | GPT-6.1 Terra | |
|---|---|---|---|---|
| Company | Anthropic | OpenAI | ||
| Type | Agent app | Frontier model | Security model | Mid-range model |
| Date | 21 Oct 2026 | GA 13 Oct 2026 | Announced 28 Oct 2026 | 26 Oct 2026 |
| Access | US Pro/Max, waitlist | API, Gemini app, AI Mode | Selected defenders | ChatGPT Work, Codex, API |
| Runs on | Claude Opus 5.5 | Google TPUs | Google TPUs | OpenAI data centres |
Key points to remember
- Duet is an app built on a model (Opus 5.5); Argon, Carbon and Terra are models you can call.
- The OpenAI model is GPT-6.1 Terra. Searches for "Terra 6.2" will not find an official model.
- All three companies now ship agents that use computers and apps, so permission settings matter more than raw benchmark scores.
- Carbon's benchmark number comes from early reporting. Check Google's own post before quoting it.
- Access is limited: Duet is US only with a waitlist, and Carbon is invite only.
How to build your own Duet-style agent with Opus 5.5
- Get a Claude API key and use the model ID
claude-opus-5-5. - Define tools for read actions (list emails, read calendar) and write actions (send email, create event).
- Run a scheduled job each morning that asks the model for a brief from the read tools.
- Route every write tool through an approval step in your app. Never let it pay or move money.
- Scan outgoing text for secrets before sending, and log every action for review.
The video at the top of this page builds these five steps live.
FAQ
When did Claude Duet launch?
On 21 October 2026, as a research preview for US Pro and Max subscribers.
Is GPT-6.1 Terra better than Sol?
It is faster and cheaper. For hard coding work OpenAI still points people to Sol and Astra.
Can anyone use Gemini 4 Carbon?
Not yet. It goes first to selected cybersecurity defenders.
Sources: Anthropic coverage on MacRumors, 9to5Google, SiliconANGLE and CNBC (21-22 Oct 2026); OpenAI developer docs and 9to5Mac (26 Oct 2026); Google Cloud Gemini Enterprise release notes (Oct 2026). Last checked 29 October 2026.