Claude Sonnet 5 Benchmarks Explained

Anthropic released Claude Sonnet 5 on June 30, 2026 as "the most agentic Sonnet yet." The headline framing is the closing of a gap: Sonnet 5 sits close to Opus 4.8 in capability, at a fraction of the price. The benchmark numbers back that framing, then complicate it. On one of Anthropic's headline knowledge-work benchmarks, Sonnet 5 actually edges past the model it's supposed to be closing toward.

Here's a walk through each benchmark Anthropic published, what the scores say about Sonnet 5 versus its predecessor Sonnet 4.6 and the higher-tier Opus 4.8, and the result that probably matters most for how teams pick models going forward.

1. Coding: SWE-Bench Pro

SWE-Bench Pro is the harder of the SWE-bench variants. Problems come from actively-maintained repositories with multi-file diffs and no public ground-truth leakage.

Source: Claude Sonnet 5 System Card, Anthropic, June 30, 2026.

Sonnet 5 lands 5 points ahead of Sonnet 4.6 and 6 points behind Opus 4.8. The 5-point jump over its own predecessor is the more meaningful number for code-heavy applications.

Cursor's CursorBench tells the same story at the IDE level: Sonnet 5 scores 57% versus Sonnet 4.6's 49%, the largest jump Cursor has reported between adjacent Sonnet releases.

2. Terminal work: Terminal-Bench 2.1

Terminal-Bench 2.1 is the eval where Sonnet 5 stops being incremental and starts being structural.

Sonnet 5 scores 80.4% on the same harness where Opus 4.8 sits at 74.6% and Sonnet 4.6 sits at 67.0%.

3. Hard reasoning: Humanity's Last Exam

Humanity's Last Exam (HLE) is the hardest general-knowledge reasoning benchmark in regular rotation. Anthropic reports two configurations: with tools and without.

Humanity's Last Exam (with tools)

Source: Claude Sonnet 5 System Card, Anthropic, June 30, 2026.

4. Computer use: OSWorld-Verified

OSWorld-Verified evaluates an agent's ability to complete real-world computer tasks across editing documents, browsing the web, and managing files on a live Ubuntu VM.

Source: Claude Sonnet 5 System Card, Anthropic, June 30, 2026.

5. Knowledge work: GDPval-AA v2

GDPval-AA v2 is the benchmark where Anthropic's framing of Sonnet 5 as "close to Opus 4.8" gets turned upside down.

Sonnet 5 scores 1,618. Opus 4.8 scores 1,615. Three points apart, with Sonnet 5 ahead.

6. Agentic search: BrowseComp

Anthropic's launch blog leads with two cost-performance curves: agentic search (BrowseComp) and agentic computer use (OSWorld-Verified).

The plot's central claim is that Sonnet 5 and Opus 4.8 now cover a single range. Sonnet 5 cheaper per task at any given accuracy, Opus 4.8 more accurate at any given spend.

Takeaways

• Sonnet 5 beats Sonnet 4.6 across every benchmark Anthropic published. The largest jump is Terminal-Bench 2.1 (+13.4 points on the same harness), the smallest is OSWorld-Verified (+2.7 points).
• Sonnet 5 lands within a few points of Opus 4.8 on five of six benchmarks, and ahead of Opus 4.8 on two: Terminal-Bench 2.1 (80.4 vs 74.6) and GDPval-AA v2 (1,618 vs 1,615).
• The Sonnet-versus-Opus decision is now accuracy-versus-cost at the margin, with the effort dial as the lever. Sonnet 5 reaches Opus 4.8 accuracy on BrowseComp at the highest effort setting, at roughly one-third the per-task token cost.
• Cyber capability is the one area Sonnet 5 is explicitly held back. The Firefox 147 eval puts Sonnet 5 at 0% working exploit, 13.2% partial. Opus 4.8 and Mythos 5 are the models for cyber work.
• Sonnet 5 ships with an updated tokenizer that increases tokens-per-input by 1.0–1.35×.