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. On Mythos vs Opus 5.5: Opus 5.5 is the model you can actually buy, and Anthropic says it matches Fable 5.1, and so the model under Mythos, on most work at a lower price.
This guide covers the whole lineup, plus Sonnet and Haiku 5.5, with prices, plan access and fast mode details as of October 23, 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 Claude Haiku 5.5 joined it on October 7.
| 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 | $0.10 | Fast | 1M tokens |
| Claude Haiku 5.5 | Oct 7, 2026 | From $0.10 / $0.50 | From $0.01 | Fastest | 1M 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 5.5 ten cents and fifty cents for prompts up to 100,000 tokens (fifty cents and two fifty above that). On October 7 Anthropic also halved Sonnet 5.5's cache read price to ten cents per million tokens. All four current models handle up to a million tokens of context and up to 128,000 output tokens. 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 multihour, 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, multihour 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.
Claude fast mode: what it is and what it costs
Claude fast mode is a faster way to run Opus, not a separate model. Anthropic's fast mode documentation says it runs the same model with a faster inference configuration, with "no change to intelligence or capabilities", and delivers up to 2.5 times more output tokens per second. The gain is in output speed, not in time to the first token, so it shows most when you stream long answers.
| Model | Fast mode input / output per million tokens | Standard price | Access |
|---|---|---|---|
| Claude Opus 5.5 | $8 / $40 | $4 / $20 | Generally available, no beta header |
| Claude Opus 5 and Opus 4.8 | $10 / $50 | $5 / $25 | Research preview, beta header and waitlist |
Prices are from Anthropic's pricing page. On the API you turn it on by setting speed: "fast" on a request. A few limits matter:
- It works on the Claude API (including Claude Managed Agents) and, for Opus 5.5, on Claude in Microsoft Foundry for Azure hosted deployments. Since October 22 it also works for Opus 5.5 on Claude Models on Google Cloud (Anthropic managed), but Anthropic's fast mode page still lists neither Amazon Bedrock nor Claude Platform on AWS.
- It is not available with the Batch API, and prompt caching and data residency multipliers stack on top of the fast price.
- It has its own rate limit, separate from standard Opus limits. Opus 5.5 gets a default fast mode limit in the Start, Build and Scale usage tiers.
- Sonnet, Haiku and Fable do not offer it.
In Claude Code you toggle it with /fast. The Claude Code fast mode page says subscribers on Pro, Max, Team and Enterprise pay for it from usage credits, not from their plan's included limits, and Team and Enterprise owners must enable it first. Turning it on partway through a conversation charges the fast uncached input price for the whole context once, so switch it on at the start of a session. Claude Code still labels the feature a research preview.
Our take: use fast mode for live debugging and quick back and forth where waiting costs you more than tokens. Leave it off for batch jobs and long autonomous runs, where it doubles the bill for time you are not watching.
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.
Where Haiku 5.5 fits
Claude Haiku 5.5, released October 7, is Anthropic's fastest model at standard speed and its cheapest current model. It is aimed at high volume, narrowly scoped work such as classification, summaries, compaction and subagent tasks under Opus or Sonnet, and Anthropic says Sonnet 5.5 and Opus 5.5 remain better for complex agentic coding. It is also the first Haiku with an adjustable effort setting. For how it compares with OpenAI's equally priced small model, see Claude Haiku 5.5 vs GPT-6 Luna.
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.
Mythos vs Opus 5.5: which one can you use?
Mythos 5.1 and Opus 5.5 are not really rivals. Mythos 5.1 is Fable 5.1 with relaxed safeguards for vetted defensive security and life science users, while Opus 5.5 is the general model Anthropic recommends as the default for everyone else.
- Capability. Anthropic says Opus 5.5 "performs at the level of Claude Fable 5.1 on most work." Since Mythos 5.1 is the same model as Fable 5.1, the gap shows up mainly on the hardest, longest tasks.
- Access. Opus 5.5 is on Pro, Max, Team and Enterprise plans and the Anthropic API. Mythos 5.1 needs approval through the Cyber Verification Program or the Life Sciences Verification Program.
- Safeguards. Fable 5.1 routes dual use cyber and life science requests to Opus models. Mythos 5.1 lets approved users run those tasks directly.
Outside those programs, pick Opus 5.5 or Fable 5.1. For how Claude compares with rival flagships, see GPT 6 Astra vs Claude Fable 5.1 and our Muse Wonder explainer.
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.
Safety testing happens before release. For what Anthropic does with flagged conversations once a model is in use, see our guide to whether Claude reports you to the police.
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.
- Use Haiku 5.5 for bulk, simple or real time tasks, and as a cheap subagent.
- 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.
From Ahzy Capital (our own products, labeled as such): Get the free AI Agent Cheat Sheet: 24 copy and paste AI agent setups for 8 types of small business, with prompts and workflows. We make and sell these, so they aren't independent picks.
Spec sheets: Fable 5.1, Opus 5.5, Sonnet 5.5, Haiku 5.5 and the release timeline.
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.
Mythos vs Opus 5.5: which is better?
Mythos 5.1 is the same model as Fable 5.1, which is Anthropic's most capable model, but only vetted organizations can use it. Anthropic says Opus 5.5 performs at Fable 5.1's level on most work, costs $4 per million input tokens and $20 per million output, and is available to anyone on a paid plan or the API.
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.
What is Claude fast mode?
It is a faster configuration of Claude Opus with the same model quality. On Opus 5.5 it gives up to 2.5 times the output speed at $8 per million input tokens and $40 per million output tokens, double the standard price. In Claude Code you switch it on with /fast, and subscribers pay for it from usage credits.
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.
