Anthropic's new Claude Sonnet 5 closes the gap to the pricier Opus model series

What happened

Anthropic calls it the most agentic Sonnet yet: it can build plans, grab tools like browsers and terminals, and work on its own at a level that just months ago only bigger, pricier models could pull off, according to the company. Sonnet 5 is meant to close that gap.

On the safety front, the model does a better job turning down malicious requests and fending off prompt injection attacks than Sonnet 4.6, according to Anthropic. Hallucinations and sycophantic behavior, the tendency to just agree with whatever the user says, are down as well. Anthropic's full safety evaluation is in the Claude Sonnet 5 System Card.

Claude Sonnet 5 is live now on all plans. It's the new default for Free and Pro users, and Max, Team, and Enterprise subscribers can access it too. Developers can plug it into Claude Code and the Claude Platform. On the API side, it goes by "claude-sonnet-5". The training cutoff is January 2026, with a one-million-token context window.

Why it matters

8. 6. 2 percent. 0 percent. 9 percent. 5 percent for its predecessor.

On the knowledge work benchmark GDPval-AA v2, which tests AI on real-world knowledge tasks, Sonnet 5 actually beats the larger Opus 4.8, scoring 1,618 to Opus's 1,615. Anthropic says feedback from early-access partners told the same story. Sonnet 5 acts far more agentically than previous versions, showing up in things like how it handles search tasks.

Lately, Anthropic has been making news for models it can't ship. The US government is blocking the company's two most capable models, Mythos 5 and Fable 5, over cybersecurity concerns. That context hangs over the Sonnet 5 launch. Anthropic is clearly eager to get ahead of any similar worries. 8 and Mythos 5.

Sonnet 5 does score a bit higher than its predecessor on these tasks, though. So Anthropic has switched on cyber safeguards by default. 8. They're dialed back compared to Fable 5's guardrails, which users complained about almost immediately. Anthropic says it views the overall cybersecurity risk from Sonnet 5 as low.

What to watch

Until August 31, 2026, Anthropic is charging $2 per million input tokens and $10 per million output tokens. After that, prices jump to $3 and $15, which is what previous Sonnet models cost.

Real-world costs might tell a different story: Because the model works more agentically, it's likely to chew through more tokens per task. So even at the same per-token rate, running Sonnet 5 could end up costing more than its predecessors. The same thing happened when Opus went from 4.6 to 4.7.