Claude Sonnet 5 (Adaptive Reasoning, Xhigh Effort)

Claude Sonnet 5 is Anthropic's most agentic Sonnet-class model, an upgrade to Sonnet 4.6 that narrows the gap to Opus 4.8 on reasoning, tool use, coding, computer use, and knowledge work while staying lower priced. It plans, uses tools like browsers and terminals, and runs autonomously for long-horizon tasks. Capability gains include SWE-Bench Verified (85.2%), SWE-Bench Pro (63.2%), SWE-Bench Multilingual (78.3%), Terminal-Bench 2.1 (80.4%), OSWorld-Verified (81.2%), BrowseComp (84.7% single-agent, 86.6% multi-agent), Humanity's Last Exam with tools (57.4%), USAMO 2026 (79.5%), GDPval-AA v2 (1618 Elo), HealthBench Professional (57.8%), and FrontierCode v1 (38.8%). It supports adaptive thinking with selectable effort levels up to 'extra high' (xhigh) and a 1M-token context window with context compaction. The safety assessment found lower rates of misaligned behavior, hallucination, and sycophancy than Sonnet 4.6, with improved prompt-injection robustness; it ships with cyber safeguards enabled by default and uses an updated tokenizer (input maps to roughly 1.0-1.35x more tokens than Sonnet 4.6). Default model on Free and Pro plans and available to Max, Team, and Enterprise users, in Claude Code, and on the Claude Platform. Launches with introductory pricing of $2/$10 per million input/output tokens through August 31, 2026, then $3/$15. Available via the Claude API as `claude-sonnet-5`.