Migrating: Sonnet 4.5 to Sonnet 5

Migrating from a generation with no effort control at all

This is a two-generation jump in effort-parameter terms: the source model predates the effort parameter entirely, relying only on the older thinking-budget mechanism, while the destination carries the full current range including its newest, highest tier. There's no existing effort setting to carry forward here — the destination's default is being adopted from a blank slate rather than migrated from a prior deliberate choice.

Why this deserves more testing than the adjacent-generation move

Because two generations of change are compressed into one migration, and because there's no prior effort setting to anchor a starting point against, this move needs more deliberate testing than a single-generation upgrade would — start from the recommended default effort level and validate against your actual task distribution, rather than assuming any specific starting point transfers cleanly from a model that never had this concept at all.

Treat this as a full migration, not a version bump

Given how much separates these two generations, this move deserves the same scrutiny you'd give any significant dependency upgrade — full re-testing against real traffic, not a quick smoke test against a couple of example prompts assumed to represent the whole workload. Start your effort-level choice from the recommended default, validate output quality and cost together against a representative sample, and only then consider whether the newest, highest tier is worth testing for your hardest cases specifically.

Related

See migrating off budget_tokens to the effort parameter for the mechanics of adopting effort-based control for the first time.