Claude Sonnet 4.5 is being retired. Anthropic is phasing out the mid-tier model from its Claude 4 lineup, meaning developers and applications pointing to that specific model version will need to migrate before the endpoint closes.
Model deprecations are routine in the AI API world - Anthropic follows a standard pattern of sunsetting older versions as newer ones become the default. Sonnet 4.6 is the current mid-tier model and the natural migration target. For most developers, the change is a one-line update: swap claude-sonnet-4-5 for claude-sonnet-4-6 in your API calls. Anthropic typically provides a transition window before hard removal, so check their model deprecation documentation for the specific cutoff date and any grace period details.
The capability gap between 4.5 and 4.6 is narrow for typical workloads - content generation, summarization, coding assistance, and Q&A should behave near-identically. The main headache is for teams running Sonnet 4.5 in automated pipelines or long-running agent workflows, where testing against the new version before cutover matters more than for one-off use cases. Consumer apps built on Claude - including Claude for Desktop and Claude Mobile - are less affected since Anthropic manages model routing on the backend. The retirement primarily impacts direct API users.