Anthropic launches Claude Sonnet 5 at a steep discount as it races toward IPO

Anthropic today released Claude Sonnet 5, describing it as "the most agentic Sonnet model yet." It becomes the default model for users on Anthropic's Free and Pro plans, while also being available to Max, Team, and Enterprise customers and on Amazon Bedrock and the Claude Platform. Introductory API pricing is $2 per million input tokens and $10 per million output tokens through August 31, rising to $3 and $15 afterward — still well below the $5 input and $25 output pricing of Anthropic's flagship Opus 4.8. On SWE-bench Pro, an agentic coding benchmark, Sonnet 5 scores 63.2% compared with Sonnet 4.6's 58.1%, and improves 13.4% on Terminal-Bench 2.1.

Beyond raw performance, Sonnet 5 features enhanced autonomy, stronger tool use and plan execution, and improved guardrails against malicious requests and prompt-injection attacks. Anthropic says the model narrowed the gap with its flagship Opus across five major evaluations and surpassed it on one, positioning Sonnet as a workhorse for coding, agents, and everyday professional tasks.

The strategic logic is unmistakable: Anthropic is democratizing capabilities that until recently only its most expensive models could deliver, while building broad-based developer adoption ahead of a confidential S-1 filing. The release lands as usage-based AI pricing pushes enterprises toward cheaper options, making a discounted near-flagship model a competitive weapon against both OpenAI's GPT-5.6 family and cheaper Chinese models.

Early reaction was mixed. Independent commentator Simon Willison noted the new tokenizer makes Sonnet 5 roughly 1.4x more expensive for English and 1.33x for Spanish, though about the same for Simplified Mandarin — a caveat that partly offsets the headline price cut. Meanwhile, an r/Anthropic thread (829 upvotes) claimed "all Claude models got nerfed BADLY," underscoring skepticism about whether benchmark gains translate to day-to-day quality.