Anthropic launched Claude Sonnet 5 on June 30, positioning the model as its most autonomous mid-tier offering and a lower-cost alternative to its flagship Opus 4.8 system. The company said the model can plan multi-step tasks, operate tools such as browsers and terminals, and complete agentic work at a level that previously required larger and more expensive models. Anthropic said Sonnet 5 narrows the performance gap with Opus 4.8 on agentic coding and computer-use benchmarks and, on at least one internal knowledge-work benchmark, outperforms it. Early access partner Zapier reported a two-part automation task ran to completion without stalling. Lovable co-founder Fabian Hedin said the model cleanly and consistently rejects unsafe requests. Security researcher Jake Williams of IANS Research told Cybernews the release represented a huge win for security teams, citing lower cost and stronger performance. Anthropic said it did not deliberately train Sonnet 5 for cybersecurity tasks and that the model has a much lower ability to perform dangerous cyber operations than current Opus models. The model ships with cyber safeguards enabled by default. The release also introduces an updated tokenizer, which Anthropic said can increase token counts by roughly 1.0 to 1.35 times depending on content, with introductory pricing designed to offset this so workloads migrating from Sonnet 4.6 cost about the same to run.