Claude Fable 5 vs Opus 4.8 — Which Frontier Model, and When

Overview

This video compares Claude Fable 5 and Claude Opus 4.8, two frontier models from the same lab, to help users determine which model to employ and when. It outlines their differences in pricing, reasoning capabilities, unique features, and ideal use cases. The key takeaway is to choose based on the specific task's difficulty, cost tolerance, and compliance needs.

In this video

• Claude Fable 5 costs $10 per million input tokens and $50 per million output tokens, exactly double the price of Opus 4.8.
• Opus 4.8 costs $5 per million input tokens and $25 per million output tokens, providing near-frontier quality at half the price.
• Both models share a one-million-token context window and support up to one-hundred-twenty-eight-thousand output tokens.
• Claude Fable 5's reasoning is always active on every call, delivering only a summarized chain of thought.
• Opus 4.8 features adaptive thinking, which can be switched on or off depending on the task's requirements.
• Fable 5 excels at the longest, hardest tasks, performing first-shot builds of well-specified systems and overnight coding runs due to its delegation capabilities and file-based memory.
• Opus 4.8 offers a fast mode that accelerates output up to about 2.5 times quicker and supports mid-conversation system prompts for steering live sessions.
• Claude Fable 5 requires a thirty-day data retention period, making it unavailable for organizations needing zero-data-retention.
• Fable 5's safety classifiers may decline requests related to cybersecurity or biology, sometimes even benign ones, necessitating specific code handling.
• The recommended approach is to use Opus 4.8 as the default workhorse for most production tasks and reserve Fable 5 for the most challenging, high-stakes jobs.

Frequently asked questions

What is the price difference between Claude Fable 5 and Opus 4.8?

Claude Fable 5 costs $10 per million input tokens and $50 per million output tokens. Opus 4.8 is half the price, at $5 per million input and $25 per million output tokens.

When should I choose Claude Fable 5 over Opus 4.8?

Choose Fable 5 for the hardest, longest tasks where a first-shot, long-horizon result is paramount, and getting it right in one pass justifies the double cost and data retention rule.

What are the unique advantages of Claude Opus 4.8?

Opus 4.8 offers half the price for near-frontier quality, a fast mode that is 2.5 times quicker, and the ability to use mid-conversation system prompts. Its writing style is also described as warmer and clearer by default.

Are there any data retention requirements for Claude Fable 5?

Yes, Fable 5 requires thirty-day data retention and is not available under zero-data-retention, which could be a significant factor for highly regulated organizations.

Does Claude Fable 5 have any limitations regarding certain content types?

Yes, Fable 5's safety classifiers can decline requests that touch upon cybersecurity or biology, sometimes even benign ones, necessitating code handling for such refusals.