Anthropic replaces Sonnet 4.6 with new default Claude Sonnet 5

Anthropic has introduced Claude Sonnet 5, its latest medium-sized model positioned between the smaller Haiku and larger Opus offerings. The company reports that this version delivers the highest level of agentic behavior among all prior Sonnet releases.

Sonnet 5 raises agentic capabilities. According to Anthropic, the model can formulate plans, operate tools including browsers and terminals, and function independently in ways that reportedly demanded bigger, costlier systems only months earlier. Its results approach those of Opus 4.8 while showing marked gains over Sonnet 4.6 released in February, especially in reasoning, tool use, coding, and knowledge-related assignments.

Sonnet 5 now serves as the standard option for both free-tier and paid Pro subscribers on the Claude platform.

Pricing starts at introductory rates through August. The release carries special introductory pricing of $2 per million input tokens and $10 per million output tokens that lasts until August 31, 2026. After that date, standard rates apply at $3 per million input tokens and $15 per million output tokens. Anthropic has raised rate limits for Chat, Cowork, Claude Code, and the Claude Platform to support greater token consumption at more intensive effort tiers; subscribers may choose the setting that best fits each task.

Additional models include Mythos 5 and Fable 5. The company also unveiled Mythos 5, described as its most powerful variant with reduced guardrails available to certain security researchers and platform operators. Fable 5 represents a more cautious alternative that appeared for customers only briefly before U.S. government intervention halted distribution; Anthropic states it is pursuing renewed availability going forward.

The company announced the release on June 30, 2026, via its Claude account on X. Sonnet 5 becomes immediately accessible to users on the platform.