anthropic releases claude opus 5.5 below opus 5 pricing

what happened

• Anthropic released Claude Opus 5.5 (claude-opus-5-5) on September 22, 2026, saying it is 'now available on all platforms, including Amazon Web Services, Google Cloud, and Microsoft Azure.'[1]
• List pricing is $4 per million input tokens and $20 per million output tokens, versus $5 and $25 for Opus 5; Anthropic says its tests show Opus 5.5 will cost 40% less than Opus 5 on typical workloads at default settings.[1]
• Anthropic's models overview lists a 1M-token context window and 128K max output, and tells developers unsure which model to use to start with Claude Opus 5.5 for most workloads.[2]
• Per the migration guide, requests that disable thinking, set a manual budget_tokens, force a tool with tool_choice any or tool, or end with a prefilled assistant turn are rejected with a 400 error, and temperature, top_p and top_k must be omitted.[3]
• Thinking tokens are billed as output tokens, so workloads that previously ran without thinking can produce more output tokens per request; the guide says to revisit max_tokens and lower the effort level to spend less on thinking.[3]
• Anthropic followed with Claude Sonnet 5.5 on September 28 and Claude Haiku 5.5 on October 7, 2026.[4]
• Anthropic's deprecations page lists Opus 5.5's retirement as not sooner than September 22, 2027, and schedules Claude Sonnet 4.5 (claude-sonnet-4-5-20250929) for retirement on the Claude API on November 30, 2026, with claude-sonnet-5-5 as the recommended replacement.[5]