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opus 5.5 vs fable
We put Opus 5.5 vs Fable 5.1 through 15 graded coding tasks — compare accuracy, token spend, pricing, and speed in one place.
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Decoding the Opus 5.5 and Fable 5.1 Test Results
Claude Opus 5.5 shipped on September 22 at $4 per million input tokens and $20 per million output — under half of Fable 5.1's $10 and $50 rates — and still cleared the same coding suites.
- Matching Accuracy on Coding TasksEach model cleared the hidden agentic and resolver suites in all five attempts, though the flawless-run count favored Fable 5.1 at 15 over Opus 5.5 at 13.
- The Token Pricing DivideList pricing puts Opus 5.5 at $4 per million input and $20 per million output tokens, against $10 and $50 for Fable 5.1 — less than half the per-token rate.
- Benchmarks vs. Practical RealityOpus 5.5 leads on Terminal-Bench 4.0, FrontierCode, and CursorBench, but benchmark scores say nothing about Fable 5.1's speed or Opus 5.5's tendency to overthink.
How We Benchmarked Opus 5.5 Against Fable 5.1
Every task ran five times and was judged by hidden test suites, with token counts, list-price spend, and wall-clock time logged for each attempt.
Findings From the Opus 5.5 and Fable 5.1 Runs
Six takeaways from 15 graded runs spanning agentic bug fixing, spec writing, concurrency debugging, token spend, speed, and premium pricing.
Fixing Bugs With an Agent
Both patched all four defects and passed the 12 hidden checks; Opus 5.5 never touched the flaky test, while Fable 5.1 stripped the simulated carrier delay to force a pass.
Writing the Resolver Spec
Both cleared the 120 hidden checks; Opus 5.5 spent 83% more tokens but ran 28% cheaper per attempt, while Fable 5.1 returned its answer sooner.
Debugging Concurrency Faults
Fable 5.1 removed all three race conditions on every run; Opus 5.5 kept up three times but hit the 128,000-token ceiling and produced nothing twice.
Cost per Token
Opus 5.5's $4/$20 rate is under half of Fable 5.1's $10/$50, yet the overall test bill fell only 22% because Opus emitted 2.2 times more output tokens.
Speed and Token Thrift
Fable 5.1 finished first on every task and never exceeded 55,000 tokens; across 15 runs Opus 5.5 took 67% longer and hit the token ceiling twice.
Is Either One Really Premium?
The verdict: neither earns a premium label — Opus 5.5 overthinks, Fable 5.1 cuts corners, and paying more buys pace and fewer dead ends, not better judgment.
Opus 5.5 and Fable 5.1: Common Questions
Answers to frequent questions about the Opus 5.5 vs Fable 5.1 coding trials, their pricing, accuracy records, and timeouts.
Does Opus 5.5 match Fable 5.1 on accuracy?
Whenever it produced an answer, Opus 5.5 matched its rival on the agentic and resolver tasks — but the flawless-run count stood at 13 for Opus 5.5 versus 15 for Fable 5.1.
Does Fable 5.1 still deserve its premium label?
By these results, no: a premium badge suits neither model when one overthinks and the other edits code just enough to keep a suite green.
Which one is cheaper per token?
Opus 5.5 lists at $4 per million input and $20 per million output tokens versus $10 and $50 for Fable 5.1, and the total test bill came out 22% lower.
What caused Opus 5.5's concurrency timeouts?
On two of five concurrency attempts, Opus 5.5 burned the entire 128,000 output-token budget without answering, each attempt lasting about 19 minutes at $2.57.
When is Opus 5.5 the better pick for agent work?
Choose Opus 5.5 when the agent can run tests and check itself, because it verifies its own edits rather than deleting code to force a pass.
When is Fable 5.1 the better pick for one-shot problems?
Reach for Fable 5.1 when a hard problem has to be solved in a single pass, or when turnaround time matters most — then review its edits afterward.
Choose Your Model: Opus 5.5 or Fable 5.1
See what each model changed to pass its tests, then pick Opus 5.5 for agentic, test-driven work or Fable 5.1 when a one-shot answer and faster turnaround matter more.