Key takeaways
- Opus 5.5 costs $4 / $20 per million tokens; Fable 5.1 costs $10 / $50. That is 2.5x more for Fable on both input and output.
- On a 2,000 in / 500 out request, Opus 5.5 costs $0.018 and Fable 5.1 costs $0.045.
- Anthropic reports Opus 5.5 performs close to Fable 5.1 on most tasks, and finished one code migration in 9.5 hours versus 12 at 51% lower cost.
- Fable 5.1 remains the safer pick for the hardest long-horizon tasks until independent results confirm parity.
- A routing policy, Opus 5.5 by default and Fable 5.1 for escalations, usually beats picking one model for everything.
When a cheaper model arrives claiming to match a premium one, the useful question is not which is better in general. It is which one delivers acceptable results on your tasks for the lowest total cost. This page sets out the verified prices, turns them into cost per task, and separates Anthropic's claims from what you should test yourself.
Price side by side
| Claude Opus 5.5 | Claude Fable 5.1 | |
|---|---|---|
| Input | $4.00 | $10.00 |
| Output | $20.00 | $50.00 |
| Cached input read | $0.20 | Check provider docs |
| Faster mode | $8.00 / $40.00 | Not applicable |
Even Opus 5.5 in fast mode is cheaper per token than standard Fable 5.1. For a full breakdown of caching and fast mode, see our Claude Opus 5.5 pricing guide.
Cost per task, not cost per token
Per-token price only tells half the story. A model that needs more tokens, more retries or more human review can cost more overall despite a lower rate. Here are three common task shapes priced on both models, assuming each finishes the job in the same number of tokens.
| Task | Tokens | Opus 5.5 | Fable 5.1 |
|---|---|---|---|
| Chat reply | 2,000 in / 500 out | $0.018 | $0.045 |
| Long document review | 50,000 in / 2,000 out | $0.24 | $0.60 |
| Agentic coding step | 40,000 in / 4,000 out | $0.24 | $0.60 |
For Fable 5.1 to be the cheaper option on a task, Opus 5.5 would need to use about 2.5 times as many tokens or fail often enough that reruns erase the gap. That is the threshold to watch in your own testing.
What the performance claims say
Anthropic describes Opus 5.5 as performing about as well as Fable 5.1 on most work, with output more than 30% faster than Opus 5. Its published code migration example had Opus 5.5 finishing in 9.5 hours against 12 hours for Fable 5.1, at 51% lower cost. These figures come from Anthropic and cover tasks it selected. Independent benchmarks were not yet available when this was written.
Where each model fits
Choose Opus 5.5 for
- High-volume production traffic such as support, extraction and summarisation.
- Coding assistance and agents where speed and cost per step matter.
- Any workload where a quick regression test shows quality holds.
Keep Fable 5.1 for
- The hardest reasoning or long-horizon tasks where a failed run is expensive.
- Workflows already validated on Fable where retesting is costly or regulated.
- Escalation paths when Opus 5.5 output fails a check.
A simple routing policy
- 01Send every request to Opus 5.5 by default.
- 02Validate the output with a cheap automated check or rule.
- 03Escalate only failed or flagged requests to Fable 5.1.
- 04Track the escalation rate weekly. If it stays low, your blended cost sits close to the Opus 5.5 rate.
With a 10% escalation rate on the chat example, the blended cost is about $0.018 plus 10% of $0.045, roughly $0.0225 per request, still half of an all-Fable setup. Model your own mix in the Claude cost calculator or compare against other providers with the comparison tool.
How to test before switching
- Pull 100 to 200 real prompts from recent traffic, including difficult ones.
- Run both models with identical settings and record tokens used, latency and pass rate.
- Compare cost per passing answer, not cost per token.
- Repeat after a few weeks, because model behaviour and pricing can change.
Frequently asked questions
- Is Claude Opus 5.5 better than Fable 5.1?
- Anthropic says it performs about as well on most tasks while costing much less. Fable 5.1 may still lead on the hardest long-horizon work. Test on your own prompts.
- How much cheaper is Opus 5.5 than Fable 5.1?
- 60% cheaper per token. Opus 5.5 is $4 input and $20 output per million tokens; Fable 5.1 is $10 and $50.
- Should I switch all my traffic to Opus 5.5?
- Usually not in one step. Route by default to Opus 5.5, escalate failures to Fable 5.1, and monitor quality and escalation rate.
About the author
AIOPLY Pricing Desk
Independent AI cost research, verified against provider documentation
Every figure in this article was checked against the provider's own pricing page before publication. Where AI assistance is used to draft a routine price report, a human editor verifies the numbers and signs it off.
Our editorial policyQuality standards
Prices were checked against provider documentation on Sep 25, 2026. Rates change without notice, so confirm current figures with the provider before committing a budget. We publish list prices only and take no payment for placement.
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