Claude Sonnet 4.5 API retirement is scheduled for November 30, 2026
Anthropic’s September 30 notice schedules Claude API retirement of claude-sonnet-4-5-20250929 for November 30, 2026 and recommends claude-sonnet-5-5. Its status table labels the date tentative. Partner-operated platforms set separate schedules.
Required action
Find claude-sonnet-4-5-20250929 in deployed configuration and usage logs. Validate Sonnet 5.5 on representative workflows before the listed November 30 retirement, including request fields, tools, thinking history and output parsing.
Deadline and replacement
| Deprecated Claude API ID | claude-sonnet-4-5-20250929 |
|---|---|
| Official notice | September 30, 2026 |
| Listed retirement | November 30, 2026 (scheduled; status table says tentative) |
| Recommended replacement | claude-sonnet-5-5 |
What the notice covers
Anthropic’s September 30 notice names claude-sonnet-4-5-20250929 and recommends claude-sonnet-5-5. The retiring model is currently documented as deprecated. This is a scheduled Claude API retirement; Kingy has not tested runtime availability.
Keep the date and platform limits
The retirement history and release note say November 30, 2026; the current status table labels its retirement-date column tentative. Amazon Bedrock and Google Cloud set separate schedules. Check the provider actually serving your configured model.
Prepare the Sonnet 4.5 migration
Use the Sonnet 5.5 guide’s sections for 4.5 and earlier callers. Audit thinking and effort settings, forced-tool assumptions, assistant prefills, replayed history, tool-input parsing and structured-output fields. Computer-use changes depend on the platform. Recount tokens and validate output and cost on your workloads.
Evidence limits
Historical first-detection date is unverified. The notice, source retrieval and local review dates do not establish when Kingy first detected this change. No model inference, account entitlement or migration was tested. Replacement guidance does not establish compatible output, access or cost.
See the existing Sonnet 5.5 migration report for the separate API-behavior changes.