Claude Opus 5 vs Fable 5: What This Comparison Is About
Claude Opus 5 vs Fable 5 is a comparison between Anthropic’s new cost-efficient flagship language model and its frontier system, measuring coding AI performance, knowledge work, agentic search, legal reasoning, and multidisciplinary analysis across standardized AI model benchmarks and real-world tasks to show which model delivers better performance per dollar and which still leads on the hardest reasoning challenges. Bottom line: Opus 5 is the default choice for most day‑to‑day coding and knowledge work, while Fable 5 still earns its place for the most demanding analytical and legal tasks where peak reasoning matters more than cost. If you are choosing a single primary LLM, Opus 5 will be the better fit for most teams, but power users with high‑stakes workflows may want both.
| Spec | Opus 5 | Fable 5 |
|---|---|---|
| Input pricing (per million tokens) | USD 5 (approx. RM23) | USD 10 (approx. RM46) |
| Output pricing (per million tokens) | USD 25 (approx. RM115) | USD 50 (approx. RM230) |
| Benchmarks won (out of 13) | 8 | 5 (remaining) |
| 3D physics simulation cost per task | USD 1.40 (approx. RM6.40) | USD 2.82 (approx. RM12.90) |
Where Opus 5 Wins: Coding, Knowledge Work, Search, and Cost
Opus 5 is designed to push performance-per-dollar rather than chase every last point of frontier capability, and the payoff is clear in coding and practical knowledge work. It beats Fable 5 on 8 of 13 internal benchmarks while costing half as much per input and output token. On Frontier-Bench v0.1, an agentic terminal coding test, Opus 5 scores 43.3% versus Fable’s 33.7%, a clear edge for complex coding workflows. On the knowledge work benchmark GDPval-AA v2, Opus 5 scores 1861 versus Fable’s 1747, again leading when the task is extracting and transforming business information. In agentic search, BrowseComp shows Opus 5 at 90.8% versus Fable’s 87.4%, meaning it is slightly better at using tools and the web to complete multi-step research tasks. In computer-use tests such as OSWorld 2.0, Opus 5 reaches 70.6% compared with Fable’s 66.1%, while clearing Fable’s peak score at roughly a third of the budget.
Where Fable 5 Still Leads: Legal and Multidisciplinary Reasoning
Anthropic is explicit that Opus 5 is not more capable overall than Fable 5. The differences show up most clearly in benchmarks that stress deep, multidisciplinary reasoning and legal judgment. On Humanity’s Last Exam, a demanding test of multidisciplinary reasoning with and without tools, Fable 5 edges ahead: with tools it scores 63.9% compared with Opus 5’s 64.7%, and without tools 56.5% versus Opus 5’s 56.3%, a small but consistent lead when the task is synthesizing complex, cross-domain arguments. On the Legal Agent Benchmark (held-out), Fable 5 scores 13.3%, while Opus 5 posts 11.7%, making Fable the safer pick for workflows that depend on careful treatment of statutes, contracts, and case law. Health and biology follow the same pattern: Opus 5 reaches 59.8% on HealthBench Professional, but the stronger Mythos-family model referenced alongside Fable scores 66.0%, and biology tests show higher human-solved figures tied to that frontier line. In short, Fable 5 and its sibling models still set the bar on the heaviest reasoning problems.
Cost, Effort Settings, and Real-World Tasks
The cost argument for Opus 5 is not only about token pricing; it is about how much money you spend to finish a task. At USD 5 (approx. RM23) per million input tokens and USD 25 (approx. RM115) per million output tokens, identical to Opus 4.8 and half of Fable 5’s USD 10 (approx. RM46) and USD 50 (approx. RM230), its raw LLM pricing comparison is straightforward. A quotable example from the release is that “Opus 5 scores three times higher than the next-best model on ARC-AGI-3,” a benchmark of novel problem-solving, while keeping costs in the same band as rivals. In a striking 3D physics simulation test where models had to build HTML scenes for a tornado, a wrecking ball, and a truck crushing a bridge, Opus 5 completed all scenarios correctly for USD 1.40 (approx. RM6.40) per task, while Fable 5 failed key physics behaviors and cost USD 2.82 (approx. RM12.90). However, higher effort settings are a shared caveat: Anthropic’s own guidance notes that max effort can cause diminishing returns and even worse performance on simpler tasks, as seen on FrontierCode where scores fell because the model added unnecessary refactors. External pilots similarly reported that more thinking can mean more hallucinations, and on a closed-book AA-Omniscience test, Opus 5 improved accuracy by 11% over Opus 4.8 while also raising hallucination rate by 6%.
Buy if / Skip if
- Buy the Claude Opus 5 if your main workloads are coding, agentic search, and day-to-day knowledge work where performance-per-dollar matters most and minor reasoning gaps are acceptable.
- Skip the Claude Opus 5 if your core tasks involve legal analysis, complex multidisciplinary exams, or health and biology reasoning where the last few percentage points of accuracy are worth paying extra for.
- Buy the Claude Fable 5 if you run high-stakes analytical workflows, legal agent systems, or research projects that benefit from the strongest general reasoning Anthropic offers despite higher token costs.
- Skip the Claude Fable 5 if you are cost-sensitive, operate many long coding or automation runs, or can tolerate slightly lower peak reasoning in exchange for halving your LLM token spend.
- Buy the Claude Opus 5 if you want a single default LLM that beats Fable 5 on 8 of 13 benchmarks while charging half the price per token and completing many tasks faster and cheaper.
