Claude Opus 5.5 vs Fable 5.1: Is Fable Still Worth 2.5x the Price?

In the Claude Opus 5.5 vs Fable 5.1 matchup, Opus 5.5 is the better buy for most people and teams. It beats Fable 5.1 on every row of Anthropic’s own comparison table and scores 58 to Fable’s 53 on the Artificial Analysis Intelligence Index, at 40% of the per-token price.

Fable 5.1 costs 2.5 times as much per token as Opus 5.5, not double. “Double” was true against Opus 5. Fable keeps a narrow case: the hardest coding problems, a few long-context tests and lower token use per task. Prices and scores are as of 24 September 2026.

Is Claude Opus 5.5 better than Claude Fable 5.1?

Yes, on nearly every published measure. Anthropic says Opus 5.5 “performs at the level of Claude Fable 5.1 on most work,” and its own launch table shows Opus ahead on all nine shared benchmarks. Artificial Analysis puts Opus 5.5 at 58 and Fable 5.1 at 53, and Opus costs $4/$20 per million tokens against $10/$50.

Anthropic admits the scores overstate the gap. Its Claude Opus 5.5 announcement says: “In our own use, the gap between Opus 5.5 and Claude Fable 5.1 is narrower than these scores suggest.” In its HAProxy rewrite, both passed nearly all regression tests, but Opus finished in 9.5 hours against 12 and cost 51% less (Anthropic-reported).

Read more: What Is Claude? What It Does, What It Costs, What It Cannot Do

For full profiles, see our Claude Opus 5.5 explainer and our Claude Fable guide.

How do Claude Opus 5.5 vs Fable 5.1 compare on price and specs?

Opus 5.5 is cheaper on every price line: $4 input and $20 output per million tokens, against $10 and $50 for Fable 5.1. Both have a 1M-token context window, 128K maximum output and adaptive thinking that cannot be switched off. The real differences are default effort, speed, cache-write pricing and plan access.

Fable figures come from the Claude Fable 5.1 model documentation. Both run on the Claude API, Bedrock, Vertex AI and Microsoft Foundry.

How much cheaper is Claude Opus 5.5 than Fable 5.1?

Per token, Opus 5.5 is 60% cheaper, so Fable 5.1 costs 2.5x as much on both input and output. Anthropic’s widely quoted “40% less to run” is a different claim: it compares Opus 5.5 with the older Opus 5 on typical workloads, not with Fable.

Cache-heavy work narrows the gap: Opus cache reads cost 80% of Fable’s, so most of an agent’s saving comes from output tokens.

Does Fable 5.1 use more of my Claude plan?

On Pro, Fable 5.1 sits outside your plan entirely. Anthropic’s help article on Claude Fable models on your plan says Pro, Team Standard and Enterprise Standard seats need pay-as-you-go usage credits. Max, Team Premium and Enterprise Premium seats can spend up to 50% of weekly limits on Fable.

The summer promotion ended on 19 July 2026 and never covered Fable 5.1. Opus 5.5 is included on Pro, Max, Team and Enterprise, though not on Free.

How do Opus 5.5 and Fable 5.1 score on Anthropic’s benchmarks?

Read more: GPT-6 Sol and Claude Opus 5.5 for L&D

On Anthropic’s Opus 5.5 launch table, Opus 5.5 leads Fable 5.1 on all nine rows, from Terminal-Bench 4.0 (66.4% vs 55.8%) to Chartography (89.0% vs 88.4%). Several gaps are within a point or two. These are Anthropic-reported results at max effort, so treat them as the vendor’s best case.

Independent re-runs of Terminal-Bench 4.0 came in lower for Opus: 59.6% from Artificial Analysis and 61.6% from Vals. The OSWorld and Chartography leads are within error margins.

Fable 5.1’s own launch table used older GDPval-AA and CursorBench versions, so never mix the two. GPT-6 Astra beats both on two rows; our GPT-6 Sol vs Claude Opus 5.5 comparison covers the OpenAI side.

What do independent tests say about Opus 5.5 vs Fable?

Artificial Analysis scores Opus 5.5 at 58 and Fable 5.1 at 53 on its Intelligence Index v4.3.2, both at max effort. Opus wins eight component evaluations and ties two, GDP.pdf and the long-context AA-LCR test. It also costs less per task, though by far less than the 60% sticker difference suggests.

The Artificial Analysis Opus 5.5 vs Fable 5.1 comparison shows Opus ahead on AA-Briefcase (1822 vs 1678 Elo), AutomationBench-AA (70% vs 59%) and SciCode (67% vs 63%). Fable scored 66 at its 1 September launch, but the index has since been re-based, so compare 53 with 58.

Does Opus 5.5 really cost less per task?

Yes, but the saving depends on effort. At max, Opus 5.5 uses about 119k output tokens per index task against 78k for Fable 5.1. That shrinks a 60% per-token saving to about 22% per task: $5.98 against $7.63 on the full index.

Lower effort brings the saving back. Artificial Analysis measures Opus 5.5 at 54 on high effort for $1.82 per task, and 51 on the default medium for $1.34. Opus on high already edges Fable at max for about a quarter of the cost.

Where is Fable 5.1 still better than Opus 5.5?

Fable 5.1’s remaining edges are narrow and come from independent testers and reviewers, not Anthropic’s table. It uses fewer tokens per task, scores slightly higher at low effort in one analysis, wins one coding metric by under a point, and some reviewers still prefer it for the hardest coding and strict template work.

• Token efficiency: 78k output tokens per task against 119k for Opus at max.
• Low effort and long context: Aivy’s analysis of Artificial Analysis data puts Fable ahead at low effort (46.8 vs 42.3) and fractionally ahead on long-context and knowledge accuracy.
• Snorkel Pass@1: Snorkel AI’s coding benchmark results give Fable a marginal Pass@1 lead, 61.5% vs 60.7%, though Opus wins the overall pass rate, 68% vs 49%.
• Hardest coding and templates: Reviewers at Every still reach for Fable on their biggest coding problems and for strict template and brand adherence in decks.

Which model is safer, Opus 5.5 or Fable 5.1?

Neither is looser. Anthropic says it deployed Opus 5.5 “with safeguards similar to those on Claude Fable 5.1,” because both are comparable to Mythos 5.1 in biology and cybersecurity. Both send flagged cyber requests to Opus 4.8 and flagged biology requests to Opus 5, so switching models will not avoid a refusal.

The differences are access and data. Vetted US organisations can reach Mythos 5.1, Fable with reduced safeguards, through Anthropic’s verification programmes; the cyber programme covers Opus 5.5 only “soon”. Fable keeps 30-day retention by default, with zero data retention for eligible customers as an interim option. Opus 5.5 offers zero data retention like previous Opus models.

Anthropic’s system card also admits a regression: Opus 5.5 is more likely to follow malicious instructions hidden in text a user pastes into a prompt.

What are reviewers saying about Opus 5.5 vs Fable?

Most reviewers have made Opus 5.5 their default and describe it as a smaller, cheaper Fable. Every’s Kieran Klaassen calls it “about 90 percent as capable as Fable at coding,” and Zvi Mowshowitz says you probably want it as your new default. The criticism centres on token use at max effort and a few tasks where Fable still wins.

In Every’s Opus 5.5 vibe check, Dan Shipper called it a “smaller Fable” that is “faster and cheaper and therefore more usable for day-to-day work.” Klaassen added: “Opus is replacing Fable 5.1 as my daily driver.” The review also found Opus ran out of time on two timed tasks and followed brand guidelines inconsistently.

Zvi Mowshowitz’s system card review says “Opus 5.5 looks like a smaller version of Fable 5.1,” allowing that some tasks still favour Fable. Simon Willison’s launch-day write-up made Opus 5.5 a default, but his max-effort pelican test failed twice at the 128K limit, costing $2.56 and nearly 20 minutes each. His best pelican still came from Fable 5.1.

Claude Opus 5.5 vs Fable 5.1: which should you choose?

Choose Opus 5.5 as your default unless you have a specific task it keeps failing. Pro subscribers get it included while Fable costs extra credits, and API teams pay 2.5x per token for Fable. Keep Fable 5.1 as an escalation model for the hardest coding.

For the wider picture, see our roundup of AI tools for developers.

How can you test Opus 5.5 and Fable 5.1 on your own workload?

Run the same real tasks through both models at matched effort levels, score them against your own pass or fail checks, and record cost per completed task rather than cost per token. Set effort explicitly, because the defaults differ: Opus 5.5 runs at medium and Fable 5.1 at high.

Step 1: Pick tasks that already hurt
Use backlog tasks that earlier models got wrong.

Step 2: Sweep Opus effort levels
Anthropic’s docs recommend an effort sweep on your own evals. The per-message effort beta changes effort mid-conversation without losing the prompt cache.

Step 3: Count the full cost of a pass
Log tokens, retries and wall-clock time for every task that passes your checks.

Step 4: Escalate only on repeat failures
Send a task to Fable 5.1 only after Opus 5.5 has failed it at higher effort.

Is Fable 5.1 being retired now that Opus 5.5 is out?

No. Fable 5.1 remains available, and Anthropic’s docs say it will not be retired before 1 September 2027. The Opus 5.5 announcement names only Sonnet 5.5 and Haiku 5.5 as arriving “in the coming weeks,” and no Anthropic page mentions a Fable 5.5 as of 24 September 2026.

Conclusion

Fable 5.1 is still strong, but no longer the obvious top pick. Opus 5.5 matches or beats it on Anthropic’s table and on Artificial Analysis, costs 40% of Fable’s per-token price, and comes included with Claude Pro. Fable’s remaining advantages are real but small.

Your next step: switch your default to Opus 5.5 at high effort, run your hardest recent tasks through both models, and keep Fable only where it passes checks that Opus fails. For options beyond Anthropic, browse our directory of AI tools and our guide to generative AI tools.