How to Use Claude Fable 5.1 and GPT-6 Astra for Free via GitLab Duo

GitLab's Duo Agent Platform ships a 30-day Ultimate trial that unlocks agentic AI chat inside your own repo — no credit card required. While the trial runs, it gives you free access to frontier models like Claude Fable 5.1 and GPT-6 Astra. Here is the exact path to get it running.

What you get

Once the trial is active, the model dropdown inside GitLab Duo Chat includes:

• Claude Fable 5.1 — Anthropic

• GPT-6 Astra — OpenAI

• Claude Haiku 4.5 — Anthropic, faster and cheaper on credits

Step-by-step setup

1. Open GitLab and create an account

Go to gitlab.com and click Sign in / Register. Sign up with email, Google or GitHub, then verify with the code sent to your inbox.

2. Create a project

Choose Create blank project. Name it anything (e.g. ai-playground), tick Initialize repository with a README, then click Create project.

3. Activate the free trial

Inside your project or group, click the Start a free trial / Try Ultimate banner (top-right, or under Settings → Billing). Enter any company name and your country, then hit Activate My Free Trial. GitLab Ultimate and the Duo Agent Platform turn on instantly.

4. Open Duo Agentic Chat

Click the

GitLab Duo Chat icon (the chat bubble) in the right toolbar of your project, and make sure Agentic mode is selected in the panel that opens.

5. Select your model

At the bottom of the chat panel, open the model dropdown and search for Claude Fable 5.1 – Anthropic or GPT-6 Astra – OpenAI, then select it. Send a quick "hello" to confirm it is working — you can switch models any time.

6. Start prompting

Ask Duo anything about your code or project — "Refactor this module," "Write unit tests for X," "Draft a merge request description," "Summarise my open issues." Duo reads your repo for context automatically.

Tip: save credits by using Claude Haiku 4.5 for quick questions, and reserve Fable 5.1 / Astra for the hard problems — one frontier message can burn multiple credits.

Good to know before you start

• The trial gives roughly 24 AI credits, and no API key is provided — this is chat access, not programmatic access.

• Trials are one per person. Creating multiple accounts to farm extra trials violates GitLab's Terms of Service.

• This is a time-boxed way to try frontier models risk-free for 30 days, not a permanent free tier — plan accordingly.

That's the whole setup: a

GitLab account, one project, and a trial activation away from frontier-model access inside your own repo.