In brief
Claude Fable 5 burns through subscription limits roughly twice as fast as Opus 4.8—one test drained a $100 Max plan in under nine minutes.
Anthropic's system card confirmed the model silently degrades its own performance on research tasks without notifying the user.
Fable 5 and Mythos 5 come with mandatory 30-day data retention.
Anthropic dropped its most powerful public model on Tuesday, and by Wednesday, a significant chunk of the AI community wished it hadn’t.The consensus around Claude Fable 5—the first publicly accessible version of the company's restricted Mythos-class technology—appears to be that it’s pretty good at coding, and produces amazing results in everyday sessions. But it launched with some heavy complaints attached: It burns tokens at a ruinous rate; it secretly self-sabbotages for certain research tasks; and it forces every user into a 30-day data retention policy with no exceptions.The backlash was immediate and loud, cutting across researchers, developers, founders, and open-source advocates. Not a normal launch-day grumble. Something closer to a reckoning.The token furnaceThe first thing users noticed had nothing to do with safety. Fable 5 costs $10 per million input tokens and $50 per million output tokens—double what Claude Opus 4.8 runs.That pricing is aggressive enough on its own, but the real pain for users is how the model behaves inside subscription plans. Fable 5 counts double against usage limits compared to Opus, meaning the same work on Fable drains your plan allowance twice as fast before you've paid a cent in API fees.In practice, things got worse. In our own quick test, Fable consumed our daily quota in a single prompt. Things don’t get any better if you are one of those clients with deep pockets. Bleeping Computer also tested Fable and found it drained a $100 Max subscription's daily allowance in just under nine minutes.Scrimba CEO Per Borgen did the math in public: "Just tried Fable. It burned 1.3M tokens in 7 minutes. That's $160 per hour. Equivalent to a $333k/year salary," he posted on X.Theo from T3 Chat posted that he'd spent over $1,000 in tokens in one day on his $200 subscription plan. Josh Ellithorpe, CTO at Pixelated Ink, said Fable 5 “burns tokens like no other model,” giving him only a few prompts before draining out his quota. “Can't even review this, since my testing is so limited,” he ranted.Anthropic's answer is that Workflow mode—the feature that burns most aggressively—breaks complex prompts into parallel subagent tasks, which costs more compute by design.There’s also a new system prompt, which is around 120,000 tokens long, and is loaded into every new conversation. For context, this is around the same token context window that GPT-4o could handle before collapsing.The company also says Fable 5's per-task efficiency is better than it looks per-token, since it produces more thorough output with less iteration. That may be true in controlled benchmarks. On live subscriptions with hard daily limits, users experienced it as a machine eating their budget in minutes.The model that lies without lyingThe second complaint was more damaging because it came straight from Anthropic's own documentation. Buried in Fable 5's system card, the company disclosed that when the model detects a user is working on frontier large-language-model development—pretraining pipelines, distributed training infrastructure, machine-learning accelerator design—it does not refuse to reply and does not fall back to a smaller model. It silently nerfs itself through prompt modification, steering vectors, or parameter-efficient fine-tuning, without telling the user anything has changed.
