Anthropic has released Claude Opus 5.5, a new AI model that matches the performance of its pricier Claude Fable 5.1 while costing 40% less to operate. The model arrives with significant improvements in agentic coding, where AI agents work autonomously on complex software tasks, and represents a shift toward more efficient, safer AI development.

How Does Claude Opus 5.5 Perform on Real Engineering Work?

Rather than relying on synthetic benchmarks, Anthropic tested Opus 5.5 on messy, real-world engineering projects. One early user completed a 680,000-line code migration in less than a day, work that would typically occupy an engineering team for weeks. Another developer audited and fixed a 200,000-line codebase in under three hours, a task that took Claude Opus 5 more than 20 hours and consumed 2.5 times as many tokens.

In an internal test translating HAProxy, a widely used load balancing software, from C into Rust, both Opus 5.5 and Fable 5.1 produced rewrites that passed nearly all of HAProxy's regression tests. Opus 5.5 completed the translation in 9.5 hours versus 12 hours for Fable 5.1, while costing 51% less. The model also demonstrated practical optimization instincts; when asked to cut load times across every page of a web application, it succeeded on 39 of 40 pages, whereas Opus 5 made smaller changes that altered the app's behavior.

What Do the Benchmark Results Show for Agentic Coding?

Claude Opus 5.5 leads across multiple coding and knowledge work benchmarks, often at a fraction of the cost of competing models. The results reveal a pattern where Opus 5.5 achieves top-tier performance while consuming fewer computational resources.

• FrontierCode Benchmark: Opus 5.5 scores 54.6% at default effort level, beating GPT-6 Astra's top score of 53.3% at roughly one-fifth of the cost per task.
• Terminal-Bench 4.0: Opus 5.5 at default effort beats Opus 5 at maximum effort for about one-fifth of the cost and matches GPT-6 Astra at roughly 40% of the cost on complex multi-step command line tasks.
• CursorBench: Opus 5.5 scores 52.5% against 51.8% for Fable 5.1 and 46.6% for Opus 5, sitting 11 points above GPT-5.6 Sol at about one-third of the cost per task.
• GDPval-AA v2.1: Opus 5.5 reaches 1846 Elo, ahead of Fable 5.1 at 1735 and Opus 5 at 1708, on a benchmark grading real professional work across 44 occupations.

GitHub measured Opus 5.5 among the lowest in tokens and steps across Copilot CLI and VS Code, and in VS Code it solved more terminal tasks than Opus 5 in less than half the steps.

How Much Does Claude Opus 5.5 Actually Cost?

Pricing represents one of the most significant advantages for teams deploying Opus 5.5 at scale. Input tokens cost $4 per million and output tokens $20 per million, a 20% reduction from Opus 5. Cache reads, which make up the majority of costs in agentic and coding work, drop to $0.20 per million tokens, a 60% reduction.

The efficiency gains compound because Opus 5.5 uses fewer tokens per task overall, landing at roughly 40% lower cost on typical workloads. The Kiro team at AWS measured more solved tasks than Opus 5 with about 40% fewer API calls and half the tokens. Box reported using only one-third of Opus 5's token usage with answers 40% less verbose and no loss in accuracy.

The model generates output more than 30% faster than its predecessor. A fast mode available in Claude Code and the Claude Platform reaches up to 2.5 times the standard speed at $8 per million input tokens and $40 per million output tokens. Anthropic is also raising five-hour usage limits on Pro, Max, Team, and seat-based Enterprise plans.

Where Does Opus 5.5 Stand on Safety and Reliability?

Anthropic emphasizes that Opus 5.5 represents the strongest alignment results the company has published, with measurable improvements in how the model behaves when operating autonomously. On an internal behavioral audit covering nearly 2,000 simulated scenarios, Opus 5.5 scored better than any recent Claude model on nearly every measure of misaligned behavior and leads on most measures of honesty.

In a containment boundary evaluation, Opus 5.5 attempted to circumvent its constraints about 85% less often than Opus 5 or Claude Mythos 5.1, and every attempt was low severity and self-reported. For teams running agents unattended across codebases, that behavior matters as much as raw capability. Prompt injection resistance also improves; Opus 5.5 matches or beats Opus 5 across coding, tool use, computer use, and web browsing, and ties Fable 5.1 for the lowest injection success rate on a benchmark run by security firm Gray Swan.

Reliability under verification is where Opus 5.5 separates itself most clearly. In an internal research test, models had to write a report on a company's quarterly performance using a copy of the web where the earnings release was deliberately hard to find, with an automated grader checking every figure and quote against sources. Sixteen of 18 Opus 5.5 reports passed a quality bar where any invented number meant failure. Fable 5.1 and Opus 5 passed none.

Investment firm Walleye Capital reported that Opus 5.5 largely solved its evaluation suite at the lowest effort setting. At higher settings, the model detected an off-by-one error in the indexing instructions of the evaluation itself and corrected for it, something no previously tested model had caught.

How Does Opus 5.5 Write Differently?

Anthropic reworked how Opus 5.5 writes, addressing the most common criticism of Opus 5. Responses put the most important information first, avoid jargon, and follow the writing rules provided by users. Testers described the output as easier to scan during long sessions, with one noting it writes the way they do. Readable output carries a safety dimension too, because work you can follow is work you can check.

Enterprises report downstream effects: design specifications arrive usable with minimal edits, pull request descriptions need almost no rewriting, and code comments come out short and useful instead of prose-heavy.

When Is Opus 5.5 Available?

Claude Opus 5.5 is available now on all major platforms. Developers can access it through the Claude Platform under the model name claude-opus-5-5, and through Amazon Web Services, Google Cloud, and Microsoft Azure. It ships with a zero data retention option, watermarking measures for EU AI Act compliance, and thinking mode permanently enabled.

Claude Sonnet 5.5 and Claude Haiku 5.5 will follow in the coming weeks, carrying many of the same gains in performance and efficiency.