Claude Sonnet 4.5

If you are still running this in production, it is the model to move first. Tentative retirement is not sooner than 29 September 2026 — the nearest date of any active model, and close enough that migration should already be scheduled.

Why it is genuinely different from Sonnet 5

Not just older. Three structural differences:

	Sonnet 4.5	Sonnet 5
Context window	200K	1M
Max output	64K	128K
Extended thinking parameter	Yes	No
Adaptive thinking	No	Yes
Price (in / out)	$3 / $15	$2 / $10

Sonnet 5 is cheaper and has five times the context. There is no cost argument for staying.

The migration cost is the thinking mode: code that sets thinking.type: "enabled" will not work on Sonnet 5, which uses adaptive thinking instead. That is a real code change, not a string swap — which is exactly why it is worth starting before September.

Specifications

Property	Value
Claude API ID	claude-sonnet-4-5-20250929
Claude API alias	claude-sonnet-4-5
Amazon Bedrock ID	anthropic.claude-sonnet-4-5-20250929-v1:0
Google Cloud ID	claude-sonnet-4-5@20250929
Reliable knowledge cutoff	January 2025

It is one of the last models with a dated ID; from the 4.6 generation onward the format is dateless but still pinned.

Finding your exposure

The Console’s Usage page exports a CSV broken down by API key and model. Five minutes there beats discovering a retired model from a production 404.