Decision guide
Should you move from Claude Opus 5 to Claude Opus 5.5?
Opus 5.5 is cheaper per token ($4/$20 vs $5/$25) and Anthropic's new default, but it changes thinking and tool-use behaviour — a same-provider upgrade that still needs a regression pass.
Switch if
- You run Opus 5 for agentic coding or knowledge work and want Anthropic's recommended default at a lower rate card.
- Your harness already uses adaptive thinking and does not rely on forced tool choice.
- The Artificial Analysis Intelligence Index v4.3.2 gap (57.6 vs 50.8 at max effort) and CursorBench 4.0 gap (57.8% vs 46.6% at Max) match what you see on your own tasks.
Stay if
- Your code forces a specific tool call or disables thinking — both now error or are unsupported on Opus 5.5.
- A regulated workflow needs a frozen, already-validated model id; Opus 5 remains Active (legacy) on the API.
- Your prompts were tuned around Opus 5's verbosity and max-effort cost is already the binding constraint.
Check before production traffic moves
- 01Replay your tool-calling suite: forced tool use and non-adaptive thinking are breaking changes.
- 02Compare cost per accepted task at the effort level you actually run, not only the $4/$20 list rate.
- 03Confirm Bedrock or Vertex availability of `claude-opus-5-5` in your region before switching production traffic.
This is a same-provider generation upgrade with a lower price, so the main risk is behavioural rather than commercial. Anthropic says Opus 5.5 performs near Fable 5.1 on most work at about 40% lower running cost than Opus 5, but the adaptive-thinking and tool-choice changes can break existing integrations.
Run a controlled trial first
A second option in a labelled pilot is cheaper than a production cutover. Score the trial, then migrate or roll back on evidence.
Pilot plan
- Freeze 20–30 representative tasks from production, including your hardest tool-calling and long-context cases.
- Run both model ids behind the same adapter and record pass rate, retries, output tokens, and reviewer minutes.
- Repeat the failing cases at a higher effort level before concluding Opus 5.5 is worse on them.
Score the trial
- Correctness
- Pass rate on fixed acceptance tests, including structured output.
- Tool-use compatibility
- Zero errors from forced tool choice or thinking configuration.
- Unit economics
- Spend per accepted task at the effort level you will run.
Migration sequence
- Remove forced tool_choice and thinking-disable parameters, then add Opus 5.5 behind a feature flag.
- Move one low-risk workload first and promote after two clean evaluation windows.
Rollback plan
- Keep the `claude-opus-5` id and prompt version in configuration for immediate switch-back.
- Replay failed tasks on Opus 5 rather than mixing outputs mid-task.
Hidden costs to price
- Max effort is verbose — output tokens can erase the lower list price on long agent runs.
- Adapter and test changes for the new tool-use rules take engineering time.
Evidence to check