Claude Fable vs Opus: Which One to Use Now That Opus Caught Up

Claude Opus 5.5 beats Claude Fable 5.1 on every benchmark in Anthropic's own launch table and costs 60% less per token. That flips the usual answer to Claude Fable vs Opus. Until September 22, 2026, Fable was the model you reached for when the work got hard, and Opus was the cheaper one that came close. Now Opus is the default, and Fable is what you escalate to when Opus falls short.

The independent numbers say the same thing. On the Artificial Analysis Intelligence Index, Opus 5.5 at High effort scores 53.6 for about $1.82 per task. Fable 5.1 at its Max setting scores 53.4 for about $7.63. This guide compares the two on benchmarks, price and plan access. It also shows how the gap moved since June, explains where Mythos fits, and ends with a simple rule for when Fable is still worth paying for.

The Key Takeaways

• Default to Opus: Anthropic's own model guide says "Most workloads start with Claude Opus 5.5" and moves you to Fable 5.1 only when Opus at xhigh or max effort still falls short.
• Price: Opus 5.5 costs $4 / $20 per million input and output tokens. Fable 5.1 costs $10 / $50.
• Plans: Opus is included on Claude Pro. Fable runs on paid usage credits on Pro and is capped at 50% of weekly limits on Max.
• Independent score: on Artificial Analysis Intelligence Index v4.3.2, Opus 5.5 leads Fable 5.1 at every effort level except Low, and costs less per task at every level.
• Mythos: Claude Mythos 5.1 is the same model as Fable 5.1 with different safeguards, open only to organizations Anthropic verifies.

Claude Fable vs Opus at a Glance

Claude Fable 5.1 and Claude Opus 5.5 share the same context window, output limit and knowledge cutoff. They differ on price, speed and default effort. The table compares the current versions, as listed in Anthropic's model documentation and pricing page.

Fable's premium does not buy a bigger context window or a longer answer. It buys a different model that Anthropic still calls its most capable one open to all customers. Whether that capability shows up in your work is the rest of this guide.

Claude Fable vs Opus Benchmarks: Opus Leads at Every Effort but Low

Claude Opus 5.5 scores higher than Claude Fable 5.1 on every benchmark Anthropic published at launch, and on the independent Artificial Analysis index at every effort level except Low. Anthropic adds its own caveat: "In our own use, the gap between Opus 5.5 and Claude Fable 5.1 is narrower than these scores suggest."

Anthropic's own benchmark table

Anthropic's Claude Opus 5.5 launch page puts Opus 5.5 ahead of Fable 5.1 on all nine benchmarks it lists for both. The table shows the seven that map most directly to everyday work. Opus 5.5 ran at Max effort, except Terminal-Bench 4.0, which ran at Xhigh.

The biggest gap is agentic coding, where Opus 5.5 leads by more than ten points on Terminal-Bench 4.0. The smallest is computer use, where the two models are about one point apart on OSWorld.

The independent read, effort by effort

The Artificial Analysis Intelligence Index v4.3.2 shows Opus 5.5 ahead of Fable 5.1 at Medium, High, Xhigh and Max effort, and cheaper per task at all five settings. The Artificial Analysis leaderboard scores each effort level as a separate entry, so each effort level compares like for like. Figures were read on October 16, 2026.

Three readings matter.

At Low effort, Fable 5.1 is the stronger model, but it costs more than four times as much per task. At Medium, the default for Opus 5.5, Opus scores higher than Fable at less than half the cost. And at the same spend of about $6 per task, Opus 5.5 at Max scores 57.6 while Fable 5.1 at Xhigh scores 53.2. For how the index is built and why versions matter, see our guide to AI benchmarks.

Two head-to-head tests Anthropic ran

Anthropic ran two direct Opus 5.5 vs Fable 5.1 tests at launch, and Opus came out ahead in both. In the first, both models translated HAProxy, a widely used load balancer, from C into Rust. Both rewrites passed nearly all of HAProxy's own regression tests. Opus 5.5 finished in 9.5 hours against 12 for Fable 5.1, and cost 51% less.

In the second, each model wrote a report on a company's quarterly results from a copy of the web where the earnings release was hard to find. An automated grader checked every figure and quote, and any invented number failed the report. Across effort settings, 16 of 18 Opus 5.5 reports passed. Neither Fable 5.1 nor Opus 5 passed in any attempt. Both tests are Anthropic's own, so treat them as evidence, not proof.

Claude Fable vs Opus Price: 2.5 Times the Rate, With One Exception

Claude Fable 5.1 costs 2.5 times as much as Claude Opus 5.5 for input and output tokens, but only 25% more for cache reads. The cache-read price matters because cached context makes up most of the bill in long agentic and coding sessions.

The token price is only half of the cost story. The other half is how many tokens each model spends to finish. On the Artificial Analysis index, Fable 5.1 costs between 1.3 and 4.3 times as much per task as Opus 5.5 at the same effort level. On subscriptions, the bill shows up differently. Anthropic's help article on Fable does not say how much of a Pro or Max limit one Fable message uses compared with one Opus message. It says only that Fable models use your limits "faster than other Claude models." For Opus 5.5 alone, our Claude Opus 5.5 launch guide covers the price cut against Opus 5 and fast mode.

Which Claude Plans Include Fable and Opus

Claude Opus is included on every paid plan, while Claude Fable is a paid add-on on Pro and a capped share of your usage on Max. Neither model is on the Free plan. These rows come from Claude's pricing page and Anthropic's help article on Fable models.

On Pro, the choice is between a model your plan includes and one you pay for by the token, and that settles it for most people.

On Max, Fable draws from the same weekly pool as every other model, so a Fable-heavy week leaves less room for Opus. When you reach the 50% Fable cap, you can keep going on usage credits or switch models. Anthropic gave eligible Pro subscribers a one-time credit when Fable 5 moved to usage credits in July 2026. Its help article says there is no equivalent credit for Fable 5.1. For how the five-hour and weekly windows work, read our Claude usage limits guide.

How the Gap Between Claude Fable and Opus Changed Since June

On today's Artificial Analysis scores, Claude Fable led Claude Opus by almost eight points in June 2026, and Opus has led since September 22. The lead changed hands three times in four months, across five Fable and Opus releases between May 28 and September 22. The table uses today's Artificial Analysis Intelligence Index v4.3.2 scores at Max effort for every pair. That makes the numbers comparable with each other, but they are not the scores the index showed at the time.

Artificial Analysis ran Fable 5 with Claude Opus 4.8 as the fallback model, the one that completes a task when Fable's safeguards step in. The price gap moved too. Fable has cost $10 / $50 since Claude Fable 5 launched, while Opus stayed at $5 / $25 through Opus 4.8 and Opus 5. Opus 5.5 cut that to $4 / $20, which widened the price ratio from 2x to 2.5x at the same moment Opus took the lead. If you are reading an older Fable 5 vs Opus 4.8 comparison, its verdict was right in June and is wrong now. Every version is covered in our full Claude model comparison.

Claude Fable vs Mythos: Same Model, Different Safeguards

Claude Fable 5.1 and Claude Mythos 5.1 are the same model with different safeguards. In Anthropic's words, "Fable 5.1 is generally available, while Mythos 5.1 is available only through our trusted access programs; its safeguards are specifically designed to support work in cybersecurity and the life sciences."

Mythos 5.1 is not a stronger tier you can buy. It is Fable 5.1 with fewer restrictions on cyber and biology work, offered to organizations verified through programs such as Anthropic's Cyber Verification Program. On Terminal-Bench 4.0, Anthropic's Fable 5.1 launch table lists Mythos 5.1 at 60.9% against Fable 5.1's 55.8%. Anthropic tested Fable 5.1 with its production safeguards switched on and says that likely lowered its scores. Opus 5.5 now ships with similar safeguards to Fable 5.1, so most cybersecurity tasks on Opus 5.5 are also re-routed, to Claude Opus 4.8. Our Fable 5.1 and Mythos 5.1 explainer covers the system card and access programs in full.

When to Use Claude Fable Instead of Opus

Use Claude Fable 5.1 only after Claude Opus 5.5 at Xhigh or Max effort has failed on a task you can check. That is Anthropic's own rule. Its model selection guide says to move to Fable 5.1 if your tests at Xhigh or Max effort "still fall short on demanding reasoning or long-horizon agentic work."

The same guide names Fable's jobs: "Agent sessions that run for hours, multistep deep research, analysis carried through to a finished document, spreadsheet, or deck." For coding, migrations and enterprise work, the guide points to Opus 5.5. In practice, raising Opus 5.5's effort is the first move, because the index table shows Opus at Xhigh beating Fable at Max for less money.

Fable 5.1 still makes sense in three situations. You run long autonomous agent sessions where Opus loses track of constraints partway through. You have a working Fable pipeline whose results you have already checked, and switching would mean re-validating it. Or you are on Max, Opus has already failed at Max effort, and you have Fable allowance left that week. On Pro, each of those cases costs usage credits, so test Opus at higher effort first.

A second opinion before you pay for Fable

When an Opus answer looks off, the cheapest check is often a different model, not a pricier Claude. Fello AI puts Claude in one picker next to GPT, Gemini, Grok and DeepSeek on Mac, iPhone and iPad. Ask the same question in the same window. You compare two answers without opening another tab or spending Fable credits. It has a free tier to start.

How to Switch Between Claude Fable and Opus on Mac

In the Claude desktop app on Mac, pick "Fable 5.1" or the Opus model from the model picker. In Claude Code, Opus 5.5 is already the default on Pro, Max, Team and Enterprise, and Anthropic's docs say neither Fable model is the default on any plan. You switch to Fable explicitly:

1. Update Claude Code with claude update. Opus 5.5 needs version 2.1.280 or later.
2. Inside a session, type /model fable to switch to Fable 5.1, or /model claude-opus-5-5 to go back to Opus.
3. To start a session on Fable, launch it with claude --model fable.
4. On Pro, the picker shows "Requires usage credits" on the Fable row, and Claude Code asks for consent before a Fable request bills credits.

Typing /model with a name also saves it as your default for new sessions. To try Fable for one session only, open the picker with /model and press s on the Fable row. If you compare the two, keep the effort level fixed, because Fable 5.1 defaults to High and Opus 5.5 to Medium on the API. To see how Opus compares with the cheaper Claude class, read Claude Opus vs Sonnet.

The Verdict on Claude Fable vs Opus

Make Claude Opus 5.5 your default and treat Claude Fable 5.1 as an escalation, not an upgrade. Opus 5.5 scores higher on Anthropic's benchmarks, higher on the independent index at every effort level above Low, and costs less per task at every effort level. On Pro it is the strongest Claude model inside your plan.

Keep Fable 5.1 for the long agent run or the deep-research job where Opus at Max has already failed your checks. That answer will flip again when Anthropic ships the next Fable, as it has flipped three times since June. Until then, start every hard task on Opus and raise the effort before you change the model.

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