Anthropic's Claude Opus 5 costs well below Fable 5 while matching or beating it across most benchmarks

Anthropic's Claude Opus 5 costs well below Fable 5 while matching or beating it across most benchmarks

Key Points

- According to Artificial Analysis, Anthropic's Claude Opus 5 is currently the most capable model, achieving an Intelligence Index score of 61, with particular strengths in analytical quality and knowledge-based tasks.

- Because Opus 5 tends to respond more frequently even when uncertain, its hallucination rate climbs to 50 percent, raising questions about reliability in high-stakes applications.

- At the "high" and "xhigh" performance levels, Opus 5 outperforms both Opus 4.8 and Sonnet 5 while maintaining lower costs.

Anthropic's Claude Opus 5 is the most capable AI model available today, according to several benchmarks, outperforming Fable 5 while costing less.

Opus 5 scored 61 on the Artificial Analysis Intelligence Index, which combines nine tests covering knowledge work, coding, scientific reasoning, and factual accuracy. That puts it just ahead of Claude Fable 5 (60), GPT-5.6 Sol (59), Kimi K3 (57), and Claude Opus 4.8 (56). Artificial Analysis worked with Anthropic to test the model before its public release.

In coding, Claude Opus 5 at "xhigh" paired with Claude Code shares first place on the Artificial Analysis Coding Index, which measures how well AI models handle programming tasks on their own, including finding and fixing bugs. On Terminal-Bench v2.1, which tests agents as autonomous engineers in real terminal environments, Opus 5 scored 89 percent at "max," matching the previous leader GPT-5.6 Sol.

For scientific reasoning, Opus 5 scored 53 percent on Humanity's Last Exam, a very difficult knowledge test covering many academic fields. That ties it with Fable 5. On CritPt, a physics benchmark from researchers at Argonne National Laboratory and UIUC, it again matches Fable 5 but trails GPT-5.6 Sol, GPT-5.5 Pro, and GPT-5.6 Terra.

Factual accuracy remains a weak spot: On AA-Omniscience, which tests the accuracy of a model's knowledge claims, Opus 5 improved by 7 points over Opus 4.8 but still trails Fable 5. Opus 5 also answers more often when it's uncertain, pushing its hallucination rate up 14 points to 50 percent.

Epoch AI confirms tight race among frontier models

Epoch AI has also tested Claude Opus 5. The research institute gave it an overall Epoch Capability Index score of 159, just below Fable 5 at 161. When looking solely at the software engineering benchmarks (SWE-ECI), though, Opus 5 ties with Fable 5 at 161, outperforming GPT-5.6 Terra and Claude Opus 4.8. GPT-5.6 Sol leads in both categories.

Overall, this confirms that the race among frontier models is tight. No single model can pull away or claim a clear advantage. That lends weight to the argument that AI models will eventually become commoditized.

Lower reasoning tiers deliver better value and coding results

The average Intelligence Index task costs $2.03 with Opus 5, less than Claude Fable 5 with fallback at $2.75. It costs more than Opus 4.8 at $1.80 and Sonnet 5 at $1.53. At the "high" and "xhigh" tiers, however, Opus 5 beats both Opus 4.8 and Sonnet 5 while costing less.

Vals.ai tested Claude Opus 5 across all five reasoning tiers using Vibe Code Bench, a benchmark for programming tasks. Scores climb from 76.7 percent at "low" to 82 percent at "medium" and 89.8 percent at "high." Performance dips at the two highest tiers, with "xhigh" scoring 88.3 percent and "max" scoring 88.4 percent despite much higher costs.

Vals.ai found that the highest tiers tend to produce more complex solutions that contain errors more often. The "high" tier produces simpler solutions that meet the requirements more reliably.

Terminal-Bench 2.1 shows a similar pattern. The "high" tier beats "max" because the model spends more time on each attempt at the top tier, leaving fewer attempts within the time limit. That matches Anthropic's guidance, with "high" set as the default tier in both the API and Claude Code.

Token pricing stays at $5 per million input tokens and $25 per million output tokens. Cache writes cost $6.25 per million tokens with a five-minute lifetime, while cache hits run just $0.50 per million tokens.

Opus 5 pulls ahead in knowledge work

Opus 5 performs especially well on the AA-Briefcase benchmark, which measures how well AI models handle typical office tasks like writing research reports, building presentations, and analyzing spreadsheets based on thousands of input files. Performance is scored across correctness, analytical quality, and presentation quality, then rolled into an Elo rating similar to chess rankings.

At max reasoning, Opus 5 reaches an Elo of 1720, a full 146 points ahead of Claude Fable 5 (1574). Its three highest tiers (max, xhigh, high) sweep the top three spots. Combined with Fable 5, Sonnet 5, and Opus 4.8, Anthropic now holds the vast majority of top-10 positions.

Cost per task dropped 20 percent to $17.79, down from $22.30 for Fable 5. The "xhigh" variant costs $14.26, and "high" comes in at just $10.41, less than half of Fable 5. Both still beat Fable 5 in the Elo ranking. At medium performance, Opus 5 hits an Elo of 1470, just behind GPT-5.6 Sol (max, 1505). At low performance, it lands at 1223 Elo, slightly below GLM-5.2 (max, 1254).

Opus 5's biggest gains show up in analytical quality. At "max," it reaches an Analytical Quality Elo of 2016, almost 300 points ahead of Fable 5. Its Rubric Pass Rate, which tracks how often the model meets predefined quality standards, sits at 58 percent ("max"), 57.2 percent ("xhigh"), and 56 percent ("high"). Presentation quality is a different story. Opus 5 scores a Presentation Elo of 1628, about 40 points behind GPT-5.6 Sol at "max" (1666).

More performance takes more time: At "max," Opus 5 needs over 36 minutes per task and averages 103 passes, about 50 percent longer than Opus 4.8 at 24 minutes and 55 passes.

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