[TLDR] Introducing Claude Fable 5 [via r/Anthropic]

Introducing Claude Fable 5: a Mythos-class model that we've made safe for general use. Its capabilities exceed those of any model we've ever made generally available.

Fable 5 is state of the art on nearly all tested benchmarks, with exceptional performance in software engineering, knowledge work, scientific research, and vision. It can run for days, and the longer the task, the larger its lead over our other models.

Fable 5 launches today alongside Claude Mythos 5. The two share the same underlying model, but Mythos 5, so far deployed only through Project Glasswing, has the safeguards lifted in some areas. The safeguards are what distinguish the two, and why we've given them different names.

Releasing a model this capable comes with risks. Without safeguards, Fable 5's capabilities in areas like cybersecurity could be misused to cause serious damage. So when Fable's classifiers detect a request related to cybersecurity, biology and chemistry, or distillation, the response is handled by Claude Opus 4.8, our next-most-capable model. Users are informed whenever this occurs, more than 95% of sessions involve no fallback at all, and performance everywhere else is unaffected. We'll keep refining the safeguards to reduce false positives.

Claude Fable 5 is available today on paid plans, in Claude Code, on the Claude API, and all major cloud platforms. Through June 22, it's included in paid Claude plans at no additional cost.

Claude Mythos 5 is available to Glasswing partners, with a broader trusted access program to follow.

URL of original post : https://www.reddit.com/r/Anthropic/comments/1u1b1yj/introducing_claude_fable_5/ Original link/media URL : https://i.redd.it/iifkdxtf4a6h1.png

TL;DR of the discussion on r/Anthropic for this post generated automatically after 200 comments.

Current source-thread comment count seen by the bot: 253.

Alright, so the general vibe on Claude Fable 5 is a bit of a mixed bag, leaning towards "wow, this thing is powerful, but also... kinda annoying to use right now."

Here's the lowdown:

The Hype is Real (Mostly): People are genuinely impressed with Fable 5's capabilities, especially in coding and complex tasks. u/ai_hedge_fund noted the SWE-Bench Pro improvement is "substantial," and u/TravalonTom even said it picked up issues missed by Gemini, Opus, and ChatGPT for months. u/Subject_Barnacle_600 is looking forward to trying it out for deep insights, even if it's a token hog.
The "Safeguards" are a HUGE Pain Point: This is where the thread gets spicy. A ton of users are reporting Fable 5 immediately falling back to Opus 4.8 for seemingly innocuous prompts, especially anything even tangentially related to cybersecurity, biology, or chemistry.
- u/UnfairFortune9840 joked about auditing a project and instantly getting "cyber flagged."
- u/CarrionCall and u/Mollan8686 both reported code review prompts triggering the fallback.
- u/RepliesAsOtherPeople is astonished you can't even discuss cybersecurity with it.
- u/dyslexda and u/rgb_panda had issues with biology-related projects.
- u/Kareja1 is frustrated that just having a genetics project in memory flags it.
- u/Odd-Librarian4630 basically says "every, single prompt I try hits the safety block."
- u/Ibasicallyhateyouall summed it up as "Guard-railed to useless."
The Pricing/Token Model is a Dealbreaker for Many: The announcement that Fable 5 will move to usage credits after June 22nd is not going over well.
- u/L1onelMess1 is "Seriously not seeing the value anymore compared to my Codex subscription."
- u/RedrumRogue is a "huge opus 4.7 and 4.8 critic" but "will never pay for credits outside of a sub."
- u/Aquosmerlda is "Already paying 100$ a month and I’ll have to pay even more otherwise I won’t have access to the latest model? Unbelievable."
- u/Moist_Firefighter211 is complaining about burning through credits super fast.
- u/fanofbreasts is annoyed it's not unlimited with a paid subscription.
Questions about "Mythos-class": Some folks are curious what makes Fable 5 a different "class" of model, as u/KlyptoK asked.
The "Free Trial" is Short: The limited-time inclusion on paid plans is noted, with some users expressing disappointment it's ending so soon. u/AdApprehensive5643 was "so happy until I read that."
Some Skepticism/Humor: There are a few comments questioning the hype or making jokes, like u/Jolly_Wrangler8976 asking if Peter Molyneux is working there, and u/fx0g saying "Well, this didn’t age well…"

The consensus seems to be: Fable 5 is a beast, but the overzealous safety filters and the upcoming credit system are making it a tough sell for many users right now. People are hoping Anthropic can dial back the false positives and reconsider the pricing model.

Posted Jul 13, 2026, 10:34 AM UTC