Claude Fable vs Opus is the choice most Claude users face now, and Anthropic's own advice is simple: start with Claude Opus 5.5 for most work, and move up to Claude Fable 5.1 only for the most demanding reasoning and long-running agentic tasks. Claude Mythos 5.1 is not a third option for most people. It is the same model as Fable 5.1 with looser safeguards, available only to vetted cybersecurity and life-science organizations.
This guide explains the whole current lineup, including Sonnet 5.5, with prices and plan access as of October 5, 2026.
The current Claude lineup
Anthropic now sells four model lines through the Anthropic API and the Claude apps: Fable at the top, then Opus, Sonnet and Haiku. The 5.5 generation started in September and is still rolling out.
| Model | Released | API price per million tokens (input / output) | Cache reads | Speed | Context |
|---|---|---|---|---|---|
| Claude Fable 5.1 | Sep 1, 2026 | $10 / $50 | $0.25 | Slower | 1M tokens |
| Claude Opus 5.5 | Sep 22, 2026 | $4 / $20 | $0.20 | Moderate | 1M tokens |
| Claude Sonnet 5.5 | Sep 28, 2026 | $2 / $10 | $0.20 | Fast | 1M tokens |
| Claude Haiku 4.5 | Oct 2025 | $1 / $5 | $0.10 | Fastest | 200K tokens |
In plain terms: Fable costs ten dollars per million input tokens and fifty per million output tokens. Opus 5.5 costs four and twenty, Sonnet 5.5 two and ten, and Haiku 4.5 one and five. All three 5-series models handle up to a million tokens of context and up to 128,000 output tokens. Anthropic says Claude Haiku 5.5 is coming "in the coming weeks." These figures come from Anthropic's models overview and pricing page.
Claude Fable vs Opus: what is the real difference?
Fable 5.1 is Anthropic's most capable generally available model. It defaults to high effort on the API, always uses adaptive thinking, and is aimed at research, greenfield projects and work that runs for hours unattended. Anthropic's Fable 5.1 announcement highlights scientific work, such as an improved elevation map of Venus built from old NASA radar data, and quotes early customers describing multi-hour, unattended runs.
Opus 5.5 is the newer, cheaper workhorse. Anthropic says it "performs at the level of Claude Fable 5.1 on most work and costs 40% less to run than Opus 5," and it generates output more than 30 percent faster than Opus 5, per the Opus 5.5 launch post. TechCrunch reported that it beats the larger Fable model on many benchmarks. Opus 5.5 also offers a fast mode with up to 2.5 times the speed, at $8 per million input tokens and $40 per million output.
So why would anyone still pay for Fable? Because "most work" is not all work. Anthropic's docs recommend Fable when your own tests on Opus 5.5, even at higher effort, still fall short. Long-horizon research and the hardest debugging are where Fable earns its price.
Pros of Fable 5.1: strongest Claude for open-ended, multi-hour work; cheap cache reads relative to its token price; best writing according to several early testers Anthropic quoted. Cons of Fable 5.1: two and a half times Opus 5.5's token price, slower, and limited access on consumer plans.
Pros of Opus 5.5: near-Fable quality at much lower cost, faster, fast mode available, Anthropic's recommended default. Cons of Opus 5.5: a few breaking API changes for teams upgrading from Opus 5, such as thinking that can no longer be turned off.
Where Sonnet 5.5 fits
Claude Sonnet 5.5, released September 28, is the speed-and-cost option. Anthropic says it is at least 30 percent faster than Sonnet 5 and costs up to 30 percent less per task. On some of Anthropic's own benchmarks it comes close to or even beats Opus 5.5, but the company is explicit that Opus 5.5 "remains clearly stronger at complex, open-ended work requiring sustained judgment." Use Sonnet 5.5 for well-scoped tasks, bug fixes, documents and slides, and high-volume workloads.
Claude Mythos vs Fable: same model, different guardrails
Mythos is the name for Anthropic's frontier model with fewer safeguards. Earlier in 2026, Anthropic held back a Mythos model from public release because it was so good at finding hidden software bugs, then released a safeguarded version months later, the BBC noted. That pattern continues: Fable 5.1 and Mythos 5.1 are "the same model, but with different levels of safeguards," in Anthropic's words.
- Fable 5.1 routes several dual-use cyber tasks, such as penetration testing, exploit generation and binary vulnerability scanning, to Opus models, and sends life-science research and development questions to Opus as well. It can be used to find software vulnerabilities, but not to develop exploits.
- Mythos 5.1 relaxes those limits for vetted users through two programs: the Cyber Verification Program for defensive security work, and the Life Sciences Verification Program, built with the US government, for professional biology research. Anthropic's security scanning product, Claude Security, also runs on Mythos 5.1.
Anthropic says Mythos 5.1 is currently available only to a set of US organizations, with wider access being coordinated with the US government. Its evaluations put Mythos 5.1's chemical and biological capabilities above Mythos 5 but below the next risk tier in its Responsible Scaling Policy.
Safety testing behind Opus 5.5
Opus 5.5 is Anthropic's first release since CEO Dario Amodei called for "pacing the frontier." It was tested before release by outside evaluators including METR and Frontier Design, and Anthropic says it is the strongest-performing model it has tested on its automated behavioral audit. Because its biology and cybersecurity capabilities are comparable to Mythos, TechCrunch reports, it ships with the same safeguards as Fable.
Which Claude model is on your plan?
According to Claude's pricing page:
- Free: Sonnet and Haiku.
- Pro ($20 a month, or $17 a month billed annually): adds Opus; Fable is available through usage credits.
- Max (from $100 a month, with five or twenty times Pro usage): Opus included; Fable can use up to half of your weekly limits.
- Team premium seats and Enterprise: Fable available, with limits set by the plan.
How to choose
- Default to Opus 5.5 for coding, analysis and writing.
- Use Sonnet 5.5 when speed or cost matters more than the last few points of quality.
- Escalate to Fable 5.1 for long, unattended or research-grade work where Opus 5.5 falls short in your tests.
- Apply for Mythos only if you are a vetted security team or life-science organization hitting Fable's safeguards.
To see how Claude's top model stacks up against OpenAI's, read GPT-6 Astra vs Claude Fable 5.1. For the safety policy behind the Fable and Mythos split, see Preparedness Framework vs Responsible Scaling Policy, and for the plan prices, ChatGPT Plus vs Claude Pro vs Google AI Pro. For OpenAI's equivalent tiers, see GPT-6 Astra vs Sol vs Luna, and for consumer plans across all four big assistants, see ChatGPT vs Claude vs Gemini vs Grok.
FAQ
Is Claude Fable better than Opus?
Fable 5.1 is the more capable model, but Anthropic says Opus 5.5 performs at Fable 5.1's level on most work for well under half the price. Anthropic recommends Opus 5.5 first and Fable for the hardest tasks.
Is Claude Mythos available to the public?
No. Claude Mythos 5.1 is available only to vetted organizations through Anthropic's Cyber Verification and Life Sciences Verification programs, currently US organizations. The public version of the same model is Claude Fable 5.1.
How much does Claude Fable cost?
Fable 5.1 costs $10 per million input tokens and $50 per million output tokens on the API, with cache reads at $0.25 per million. On Claude Pro it is accessed through usage credits, and on Max it can use up to half of the weekly limits.
Should I use Claude Opus 5.5 or Sonnet 5.5?
Use Opus 5.5 for complex, open-ended work that needs sustained judgment. Use Sonnet 5.5 for faster, well-scoped tasks and high-volume use; it costs half as much per token.
Is Claude Opus 5.5 free?
No. The free Claude plan includes Sonnet and Haiku. Opus 5.5 requires Pro, Max, Team or Enterprise, or API usage.