🧭 Claude Opus 3 API Access Retired — Migrate to Opus 4.5

Anthropic has officially retired API access to Claude Opus 3 (claude-3-opus-20240229) today, completing the 3.x generation's transition to legacy status. As of today, API calls to the Opus 3 model identifier return errors, and developers with active integrations must update their code to use a Claude 4.x model. Anthropic's recommended migration target is claude-opus-4-5, which delivers substantially stronger performance — including significantly improved reasoning, instruction-following, and tool use — at approximately one-third of the per-token cost.

Migration guide highlights

• Model identifier change — replace claude-3-opus-20240229 with claude-opus-4-5 in all API calls; no other request schema changes are required for most use cases
• Capability improvements — Opus 4.5 outperforms Opus 3 on all major capability benchmarks; the 200K token context window is standard (Opus 3 shipped with 200K by default as well, so no context window adjustments are typically needed)
• Cost reduction — Opus 4.5 is priced at approximately one-third the per-token cost of Opus 3, meaning the migration reduces API spend for most customers while improving output quality
• Claude.ai access — Opus 3 remains accessible for paid Claude.ai subscribers via the model selector for a transitional period; the API retirement is specific to programmatic access

🧭 Webhook Integration Guide — Event-Driven Claude Deployments

Anthropic has published a comprehensive Webhook Integration Guide covering how to build event-driven pipelines that integrate Claude into existing infrastructure without constant polling. The guide addresses three common patterns: triggering a Claude analysis when a new document arrives in a storage bucket, chaining multiple Claude calls in response to a customer support ticket event, and using Claude as an async step in a data-processing workflow.

The guide introduces a lightweight webhook verification pattern using HMAC-SHA256 request signing, which ensures that only legitimate Anthropic-originated callbacks are processed by the receiving endpoint. It includes ready-to-run examples in Python (FastAPI), TypeScript (Express), and Go. A companion reference covers retry logic: Anthropic's webhook system retries failed deliveries up to five times with exponential backoff, and provides a replay endpoint for manually re-delivering events that were missed during a receiver outage.