What to Do Before Claude Sonnet 4.5 Shuts Down on November 30, 2026
Anthropic retires claude-sonnet-4-5-20250929 on the Claude API on Nov 30, 2026. After that date, requests to it fail. Anthropic's recommended replacement is claude-sonnet-5-5. 2026-11-30
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The facts (from official pages)
| Model ID | Platform | Shutdown | Replacement (provider wording) |
|---|---|---|---|
claude-sonnet-4-5-20250929 | Anthropic | Nov 30, 2026 | claude-sonnet-5-5 · source |
anthropic.claude-sonnet-4-5-20250929-v1:0 | AWS Bedrock | Apr 8, 2027 | not listed · source |
- Anthropic deprecated
claude-sonnet-4-5-20250929on Sep 30, 2026 and retires it on the Claude API on Nov 30, 2026 (Anthropic model deprecations). - AWS Bedrock is different:
anthropic.claude-sonnet-4-5-20250929-v1:0was marked deprecated on Oct 8, 2026 with a shutdown date of Apr 8, 2027. AWS does not list a replacement on that page (AWS Bedrock model lifecycle). - Google Vertex AI: Vertex publishes its own retirement dates for partner models. Our parser could not read Google's Vertex deprecations page reliably this week, so check Google's page directly. Do not assume it matches the Claude API date.
Step 1: Find every place you call it
rg -n --hidden -g '!node_modules' 'claude-sonnet-4-5' .
rg -n --hidden -g '*.{yml,yaml,json,toml,tf,tfvars}' -g '.env*' 'sonnet-4-5' .
- Check CI workflows, Dockerfiles, notebooks, eval configs, LLM gateway/router configs, feature flags and prompt registries stored in a database.
- On Bedrock, the ID looks like
anthropic.claude-sonnet-4-5-20250929-v1:0(often with a region or inference-profile prefix); search forsonnet-4-5to catch every form.
Step 2: Map each call to its platform and date
The same model retires on different days depending on where you call it. Write down, per call site: platform (Claude API / Bedrock / Vertex / gateway), model ID, shutdown date, owner.
Step 3: Test the replacement
- Run
claude-sonnet-5-5against a frozen set of real prompts and compare quality, refusals, latency and cost. - Tool use: confirm every tool call still validates against your schemas and that multi-step tool loops end the same way.
- Structured output: parse 100% of responses with your real JSON parser, not by eye.
- Parameters: re-check max output tokens, thinking/extended-reasoning settings and any beta headers against Anthropic's docs for the new model.
Step 4: Roll out in stages, well before Nov 30
- Put the model ID in config, not code, so rollback is one change.
- Shadow traffic first, then 1% → 10% → 50% → 100%.
- Aim to finish at least a week before Nov 30, 2026.
Step 5: Guard against the day-after failure
- Alert on model-not-found / 404 errors from the Anthropic SDK.
- Add a CI check that fails if
claude-sonnet-4-5-20250929appears in the repo after the cutover.
Grep commands for code/YAML/Terraform, direct API vs Bedrock/Vertex/Azure date diff, replacement parity matrix, eval + shadow-traffic cutover, post-shutdown 404 guardrails. Preview it, or get it now:
FAQ
When does Claude Sonnet 4.5 shut down?
On the Claude API, claude-sonnet-4-5-20250929 retires on November 30, 2026 (deprecated September 30, 2026), per Anthropic's model deprecations page.
What should I replace Claude Sonnet 4.5 with?
Anthropic lists claude-sonnet-5-5 as the recommended replacement.
Does the date apply on AWS Bedrock?
No. On AWS Bedrock, anthropic.claude-sonnet-4-5-20250929-v1:0 has a shutdown date of Apr 8, 2027 per the AWS Bedrock model lifecycle page. Check Google Vertex AI's own model page separately.
Dates come from official provider pages and are re-checked daily. Always confirm on the linked source. Related: all Anthropic shutdowns · AWS Bedrock · all guides