Anthropic releases Claude Sonnet 4.5
Confirmed
Importance: major (4 of 5)The takeaway
Claude Sonnet 4.5 became the state-of-the-art model on SWE-bench Verified and OSWorld, able to maintain focus on complex tasks for over 30 hours; Anthropic also launched the Claude Agent SDK and Claude Code 2.0.
Status
- Claim
Confirmed
- Our reporting
- High confidence
- Importance
- Major (4 of 5)
- Last verified
- 11 October 2026
Your AI and this story
- GPT-6 AstraIn its training data
- Claude Opus 5.5In its training data
- Gemini 4 HydrogenIn its training data
- Grok 4.7In its training data
It happened before the cutoffs of all four assistants, so it can be in their training data.
Key facts
- Released 29 September 2025
- SWE-bench Verified: 77.2%, per Anthropic
- OSWorld: 61.4%, per Anthropic
- Observed working autonomously for more than 30 hours on complex tasks
- Same price as Sonnet 4: $3 / $15 per million tokens
What happened
Anthropic released its best coding and computer-use model at the time, alongside the building blocks behind Claude Code as a general agent SDK.
Why it matters
Pushed the length of tasks AI agents can reliably do and made agent-building infrastructure broadly available.
Sources
3 sources from 1 site. Numbers match the chips in the text.
3 sources: 3 primary
Primary
- Anthropic Engineering: Effective context engineering for AI agents (Sept 29, 2025)anthropic.com, official
- Introducing Claude Sonnet 4.5 (Anthropic)anthropic.com, official
- Introducing Claude Haiku 4.5 (Anthropic)anthropic.com, official
Changes
- Added related Anthropic engineering post link(s)
- Filed