What is Claude Opus 5, and how is it different from Sonnet 5?

What Opus 5 and Sonnet 5 are

Anthropic ships its Claude models in named families, each with its own positioning. Opus 5 is the top-of-line family: the largest, most expensive, and most capable, aimed at the hardest reasoning, agentic, and long-context tasks. Sonnet 5 is the middle family, tuned for everyday coding, chat, and tool use at a lower price and higher speed. The two share the underlying family but trade off depth, latency, and cost.

Anthropic\u2019s product pages and API documentation treat the two as the primary workhorses of the current lineup, with a smaller Haiku family for low-latency, low-cost tasks and Claude Code as a product surface on top. Pricing, exact capability flags, and rate limits change frequently; the durable distinction is what the family is for, not the specific plan numbers.

What is in the Opus 5 System Card

The Anthropic Opus 5 System Card is the most detailed public source on what Opus 5 is and how Anthropic evaluated it. Schneier\u2019s 2026-07-31 post quotes page 73 directly: on the IPI prompt-injection benchmark, Opus 5 reduces attacker success within 15 attempts from 5.5% (Opus 4.8) to 2.0% (Opus 5), and from 0.5% to 0.2% on a single attempt. The same chart shows Sonnet 5 at 5.9% at k=15 and a non-Claude frontier range from 16.5% (Muse Spark) to 43.9% (GPT 5.6 Luna).

The System Card also defines an autonomy threat model that applies when the deployment has three conditions at once: high reliance, sensitive access, and capable of subterfuge. On stealth evaluations (page 117), Opus 5 measured at 4\u20135% and 1% on different runs, behind Mythos Preview on the same measure. The point of these numbers is not to crown a winner - it is to make the risk profile concrete enough that deployment teams can read it. A model that publishes a System Card is also a model whose vendor has decided to attach specific safety claims to specific behaviours.

How Opus 5 and Sonnet 5 differ in daily use

In practice, the biggest difference between Opus 5 and Sonnet 5 is not benchmark number X - it is the trade between quality and cost. Opus 5 is the model you reach for when the task is genuinely hard: a long context, a multi-step agent, an architectural review, a tough debugging session. Sonnet 5 is the model you reach for by default for everyday coding, chat, and tool use, because it\u2019s fast and cheap enough to use as the workhorse.

Many teams end up routing automatically: Sonnet 5 first, Opus 5 when the task escalates. The escalation trigger is usually one of three things - context length getting long enough that the smaller model loses track, a multi-step agentic workflow that needs to plan ahead without losing the thread, or a hard single-shot task (a complex refactor, a security review) where the quality bar matters more than the cost. Teams that route Opus 5 first often regret the bill; teams that route Sonnet 5 first and never escalate miss the model\u2019s best behaviour.

• Sonnet 5: everyday coding, chat, small-to-medium tool use, faster iteration loops
• Opus 5: hardest reasoning, long context, multi-step agents, code review on subtle changes
• Hybrid routing: start on Sonnet 5, escalate to Opus 5 when context gets long or the task gets hard

What did not change between the two

Both models share the same Anthropic safety posture, the same Claude Code product surface, and the same tool-use API. Both models are subject to the same Anthropic usage policy, the same training-data opt-out controls, and the same enterprise / consumer boundary. If you are evaluating Claude for a deployment that touches sensitive data, the model-family choice is usually secondary to the deployment boundary (consumer vs API vs enterprise, plus the specific data-control settings).

Both models are also subject to the same general limits: prompt injection is not solved in the general case (see the related RepoRadar answer on prompt injection), long context still degrades, and the model can still hallucinate. Choosing between Opus 5 and Sonnet 5 does not move any of those fundamentals. The choice moves quality on hard tasks and price on everything else.

Limits of this answer

Pricing, exact feature availability, and rate limits change faster than the model names. Treat any specific number (per-token price, plan limits, availability of extended thinking, computer-use rollout) as a snapshot for context, not a current state. Verify on Anthropic\u2019s product and API documentation at the moment of decision. RepoRadar does not publish a current 'Opus 5 vs Sonnet 5 leaderboard' because the right answer changes faster than we can responsibly re-verify it.

The Opus 5 System Card is the current primary source for the model\u2019s capability and safety claims. It is a vendor document and an independent read (Schneier\u2019s post is one example) is still the best way to use it. The durable parts of this answer are the positioning of the families and the routing pattern; the specific numbers will move.

A useful next action

Pick three of your real tasks - one easy coding task, one medium review task, one hard multi-step task - and run each on Sonnet 5 and Opus 5 with the same prompt. Compare the diff size, the number of follow-ups, and the cost. Then set the routing rule for your team: Sonnet 5 by default, Opus 5 when the context gets long or the task gets hard. Re-run the same exercise quarterly; the family positioning is stable but the price and capability boundaries move.