Anthropic Publishes a Claude Model Selection Guide: Start Most Coding on Opus 5.5 at Medium, Tune Effort Before Switching Models, Put Subagents on Haiku 5.5
On November 9, Anthropic's developer blog claude.dev published a selection guide by Addy Osmani, "Which Claude model should you build with?"; the ClaudeDevs post drew about 9,200 likes and 12,000 bookmarks. The core advice: start most coding and knowledge work on Opus 5.5 at medium effort (the Claude Code default); drop to Sonnet 5.5 for well-scoped bug fixes and spec-driven work; use Haiku 5.5 for classification, routing, extraction, and log-reading subagents; and move up to Fable 5.2 for major refactors, migrations, and deep research. Before switching models, tune effort and give the model a way to verify its own work. The guide also lists prices, default effort levels, and compatibility differences that can trigger 400 errors when migrating.
Key Takeaways
- Prices (vendor figures, per million input/output tokens): Haiku 5.5 $0.10/$0.50 ($0.50/$2.50 above 100K), Sonnet 5.5 $2/$10, Opus 5.5 $4/$20, Fable 5.2 $8/$40; all four have a 1M context window and 128K max output
- Anthropic's own FrontierCode 2.0 runs: Fable 5.2 at high scores 45.3% vs Opus 5.5 at max 45.5% for roughly half the cost per task, so test Fable before pushing Opus past high
- On a SWE-bench Pro subset, running Opus 5.5 at low and re-running failures at high passed about 97% at about $0.17 per task, versus 95.3% at $0.29 with everything at high
- An Opus 5.5 lead over up to 25 parallel Sonnet 5.5 workers searching about 22 million tokens of code cost about a third less than Opus alone, with a similar score
- Migration traps: Fable 5.2 enables preserved thinking on all API accounts, so editing earlier context returns a 400; tool_choice any/tool also returns 400 on Sonnet 5.5, Opus 5.5, and Fable 5.2
