Claude Sonnet 4.5 launched September 29, 2025 with Anthropic highlighting coding, computer-use and agent-related improvements. These are model release claims, not proof that a raw API deployment has autonomous file access. By the October 25, 2026 cutoff Anthropic had announced deprecation on September 30 and scheduled retirement for November 30, 2026; the retirement had not yet happened.
Historical research cutoff: 25 October 2026. Primary-source historical claims are date-scoped; cloud entitlements, region-specific availability, current pricing and rate limits are not implied.
Release identity at a glance
- Provider
- Anthropic
- Model family
- Claude Sonnet 4.5
- Public launch
- 2025-09-29
- API ID / checkpoint
- claude-sonnet-4-5-20250929
- API retirement status
- Not confirmed as retired at the research cutoff
The release and why it mattered
Anthropic’s public report accompanied the release with benchmark methodology, including configurations for SWE-bench Verified and tool-assisted evaluations. The figures are provider-reported and depend on prompts, tools, token budgets and sampling. A head-to-head comparison that ignores those elements gives readers a misleading impression of objective ranking.
Capabilities and genuine use cases
For a software task, a newer model can improve planning and code understanding without eliminating compilation errors, dependency conflicts or unsafe assumptions. A controlled deployment should isolate credentials and sensitive repositories, log tool invocations and gate executable changes behind tests or human confirmation. This article treats model ability, not product orchestration architecture.
Integration and version identity
The API identifier `claude-sonnet-4-5-20250929` is a dated snapshot. Migration planning must account for the September 30, 2026 deprecation notice and the scheduled November 30 shutdown, recording the latter as future at cutoff. Partner-operated platforms may publish different schedules and should not inherit Anthropic-operated dates automatically.
Limits and evidence gaps
The original 2025 launch offered product-specific subscriptions and developer access, but those cannot be assumed unchanged in October 2026. Likewise, public benchmark leadership claims are historical vendor viewpoints, not site-authored independent tests.
How to choose or migrate
Sonnet 4.5 is valuable as a late-2025 reference for agent-capable coding models and as a live example of the distinction between deprecated and retired. Before deploying, compare supported successor models against a fixed acceptance suite and obtain AI 10’s current cost snapshot.
Reproducible evaluation checklist
For older Claude services, compare the vendor-operated API lifecycle with the lifecycle published by the actual cloud partner. Exercise long inputs, structured outputs and tool argument validation as separate acceptance tests. Do not assume that matching family names imply identical backend checkpoints.
Collect the exact Messages API version, system instructions and model string from a reproducible request. An active cloud model and a retired direct-API model can coexist under similar product naming.
Sources & Further Reading
- www.anthropic.com — documentation/reference (supplier-provided reference; not independently checked in this pass)
- platform.claude.com — documentation/reference (supplier-provided reference; not independently checked in this pass)
Source documentation establishes vendor-published facts, not independently measured model quality, tenant access, contractual rights or current prices. Use a dated pricing ledger and an account-specific entitlement check for deployment decisions.