Model
AI model
Claude Fable 5 or Claude Haiku 4.5. Same idea as car models: one company, different sizes and trade-offs. In Claude Code you can switch models with the /model command. Pick a bigger model for hard problems, a faster one when you're churning through quick tasks.
Claude ships as a family of models — same company, same values, very different capabilities and costs. Think of them as hiring the right person for the job:
| Model | Speed | Cost | Best for |
|---|---|---|---|
| Haiku 4.5 | Fastest | Lowest | Quick edits, lookups, simple one-liners |
| Sonnet 5 | Balanced | Mid | Most coding tasks, writing, explaining (the default) |
| Opus 4.8 | Deep | High | Hard architecture decisions, subtle bugs, deep multi-file reasoning |
| Fable 5 | Deepest | Highest | The hardest problems — top scores across nearly all benchmarks |
Sonnet 5 is the Claude Code default — the newest Sonnet-tier model, closing much of the gap to Opus-level reasoning while staying fast and affordable. It handles the vast majority of everyday tasks well.
Opus 4.8 is the specialist: slower and more expensive, but it reasons deeper and holds more context. Reach for it when a hard problem keeps stumping Sonnet.
Fable 5 (released June 2026) is the most capable publicly available Claude model, built on the Mythos research tier. It leads on software engineering, knowledge work, and scientific reasoning. Reach for it when Opus still isn’t enough.
Haiku 4.5 is the sprinter: cheap and fast, ideal for high-volume quick tasks where you already know roughly what you want and just need execution.
Switch with /model — Claude Code shows a menu, or you can type the full model id directly.
What about Mythos? Claude Mythos is the underlying research model that Fable 5 is based on, deployed with certain safety restrictions lifted for a small group of security partners (Project Glasswing). It’s not publicly available.