Anthropic’s latest located Claude model upgrade is Claude Sonnet 5.5, announced on September 28, 2026. Anthropic says it is 30% faster and costs up to 30% less than Sonnet 5 for most work. The company’s API documentation lists Sonnet 5.5 as active and recommends it as the replacement for Sonnet 4.5, which is scheduled to retire on November 30, 2026.
What’s new in Claude Sonnet 5.5?
Anthropic’s newsroom index describes Sonnet 5.5 as a clear upgrade over Sonnet 5. The reported gains are general comparisons from Anthropic, not independently verified results; the announcement summary does not provide task-level benchmark details. Anthropic’s newsroom lists the announcement dated September 28, 2026.
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Is Claude Sonnet 5.5 faster or cheaper than Sonnet 5?
Anthropic reports that Sonnet 5.5 runs 30% faster and costs up to 30% less for most work than Sonnet 5. “Up to” matters: the stated cost reduction is not a guaranteed saving for every request or workload. The available announcement summary does not specify measurement conditions or provide enough detail to compare particular tasks.
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Is Claude Sonnet 5.5 available in the API?
Yes. Anthropic’s model deprecation documentation lists claude-sonnet-5-5 as an active API model, with tentative retirement no sooner than September 28, 2027. That API listing does not establish whether or how the model is available through Claude.ai plans, in particular regions, or at a specific end-user price. Check Anthropic’s current documentation for status before making deployment plans: model deprecations.
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What should developers migrate to from Claude Sonnet 4.5?
Anthropic lists Sonnet 5.5 as the recommended API replacement for Sonnet 4.5. The documentation says Sonnet 4.5 was deprecated on September 30, 2026, and is scheduled for API retirement on November 30, 2026. The recommendation identifies a target model; it does not establish that an application can switch without code or behavior changes.
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- Review the live Anthropic deprecation documentation before setting a migration date, since model status and retirement schedules can change.
- Update the model identifier in your integration to
claude-sonnet-5-5, then test the application against its actual prompts and workflows. - Complete the migration before the scheduled November 30, 2026 API retirement of Sonnet 4.5, allowing time to address any integration or output differences.
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