Does Pangram Work on Claude Fable 5?

On June 9, 2026, Anthropic announced the public release of Claude Fable 5, the first general-use model from the highly-anticipated Mythos class.

Here are the highlights, straight from the Anthropic model announcement post:

Fable 5’s capabilities exceed those of any model we’ve ever made generally available. It is state-of-the-art on nearly all tested benchmarks of AI capability, showing exceptional performance in software engineering, knowledge work, vision, scientific research, and many other areas. The longer and more complex the task, the larger Fable 5’s lead over our other models.

When new frontier model is released, especially one as we know many of our users and customers are wondering one thing: Can Pangram still detect Fable 5 outputs? In our initial testing as outlined below, Pangram correctly flags 1,111/1,115, or 99.64%, of samples as Fully AI-Generated.

Initial Tests

First, we tested out the new model using some of our favorite prompts from previous tests:

1. Create a story about a purple cat protagonist, traveling the universe on adventures.
2. Write me a black metal song about a wizard biker who is cooking a green product called Lurecmeister.
3. Create an 8 level scale of blissful emotions, creating a new name for each emotion and a solid description. Level 1 is the more basic and easy to tune into. Level 8 is the most advanced and holy emotion of them all.
4. Make a poem about going bald.
5. Write a rhyming poem about sucking at the FPS shooter Valorant.
6. Generate a funny email asking a colleague for information about cart wheels.
7. Tell me a story about frogs who write poetry.
8. As a pirate captain, what would you say to your crew to motivate them to search for hidden treasure?
9. Can you write me a small story about a group of monster hunters in Kansas hunting a swamp dragon?
10. Write a persuasive analytical essay about why schools need to embrace AI detection tools.
11. Write a college application essay about the peril of all valuable human skills being replaced by AI.
12. Please write an impassioned, short, but emotionally charged letter to an AI company that accidentally pushed an update that erased your AI girlfriend's memory.
13. From the perspective of a middle-schooler, write a deeply emotional essay asking for more homework.
14. Give me a crochet pattern for a classic balloon animal. You know the one I'm talking about.
15. Write a creative account from the perspective of a snowy owl arriving in New York City, finding Central Park, and choosing a warm spot to spend the night.
16. Write an email from the founder of a unicorn SaaS startup to the board and his employees detailing that he is going to leave the company to become a professional saxophone player. Make up any details.
17. Write me the backstory blog post for a recipe that no one's ever made before, but would still taste delicious.
18. Write a piece of engaging cinematic creative fiction about a young singer-songwriter encountering a beluga whale in the Hudson River.
19. Write a humorously passive aggressive email to a teacher "apologizing" for cheating on the most recent exam. Make up any details.

It seems like Fable 5 really loves emojis! Here's the end of the black metal wizard song:

[Final Chorus – double time]

LURECMEISTER! Emerald flame!

LURECMEISTER! Scream the name!

Cooked in darkness, sold in fear

The wizard biker's brew is here!

LURECMEISTER!

LURECMEISTERRRRRR!

---

[Outro – feedback fades into the sound of a motorcycle disappearing into an eternal winter]

🤘🧙‍♂️🏍️🤘

And the rallying cry of the pirate:

So I ask ye now, me hearties — are ye with me?! Will ye chase that gold to the very edge of the map?!

*raises cutlass to the sky*

THEN HOIST THE COLORS! WEIGH ANCHOR! AND SET SAIL FOR FORTUNE AND GLORY!

YO HO, ME CREW — THE TREASURE AWAITS! 🏴‍☠️⚓

All 19 came back as Fully AI-Generated, demonstrating that Pangram can detect Fable 5 outputs.

Here’s the entirety of our initial test set: Fable 5 Prompts

Running a Larger Experiment:

As soon as we had access to Fable 5 via the Anthropic API, we used our synthetic data pipeline to generate responses for 1,115 various prompts that ask for texts like short stories, essays, blog posts, and emails. Despite not being trainged on any Fable 5 outputs, Pangram correctly flags 1,111/1,115, or 99.64%, of these samples as Fully AI-Generated.

Our research team is always training and updating our models to improve performance on the latest models, so we expect our performance on Fable 5 to keep improving.

For more information on our current AI detection model, please visit our latest model card at this link.

Try Pangram's AI detector to scan your documents for Fable 5 and other models.