Claude Opus, Fable, Sonnet and Haiku: which model to choose in 2026?
Opus 5.5, Fable 5.1, Sonnet 5 and Haiku 4.5 serve different jobs. Compare use cases, API prices and access without mistaking Max 20x for a model.
Four names, but not four versions of the same model
The Claude family is not a simple ladder where the highest version number replaces everything else. As of September 27, 2026, Anthropic's announcements highlight Opus 5.5, Fable 5.1, Sonnet 5 and Haiku 4.5. They make different trade-offs between depth, speed and cost. Their version numbers differ because the branches advance at different rates.
Start with your task. A long software migration does not need the same model as a batch of short summaries. The right choice is the one whose results survive review at an acceptable total cost and turnaround time.
| Model | Good starting use | Watch for |
|---|---|---|
| Haiku 4.5 | Short requests, classification, extraction and volume | Review ambiguous cases before automating |
| Sonnet 5 | Daily production, focused coding, documents and tools | Escalate work that resists a first pass |
| Opus 5.5 | Complex projects, audits and long-running coding work | Verify conclusions and real-world changes |
| Fable 5.1 | Another frontier choice for demanding, extended work | Compare its output with Opus on your own tasks |
Sonnet 5: start with the versatile option
Anthropic positions Claude Sonnet 5 as better at planning, tool use and multi-step work than Sonnet 4.6. It is a practical first choice for an article grounded in sources, a document review, an export analysis or a focused software feature. It can be excessive for a trivial repeated extraction and insufficient for a project where one error cascades through many steps.
Opus 5.5 and Fable 5.1: two choices for difficult work
Opus 5.5, announced on September 22, is Anthropic's new leading model for agentic coding and knowledge work. Anthropic places it near Fable 5.1 on many tasks, generally at a lower running cost. It is a strong candidate for code migrations, evidence-heavy analysis and multi-stage audits.
Fable 5.1 remains a distinct frontier model. It may still fit demanding projects or an established workflow already validated with it. Do not declare a universal winner from a benchmark chart: use the same documents, effort level and success criteria, then compare accuracy, revisions, time and total cost. Vendor benchmarks are reference points, not guarantees for your workload.
Haiku 4.5: speed on well-scoped tasks
Haiku 4.5 is the small model in this verified selection. It suits first passes over many records, tagging a corpus or short answers with a defined format. Let Haiku handle straightforward cases and pass uncertain ones to Sonnet or Opus. Speed helps only when the human correction rate remains low.
API prices are not subscription prices
These public Anthropic prices were checked on September 27, 2026. They are per million input and output tokens for direct API usage, not the price of a Claude subscription or access through Rankerfox.
| Model | API input | API output |
|---|---|---|
| Haiku 4.5 | $1 | $5 |
| Sonnet 5 | $2 | $10 |
| Opus 5.5 | $4 | $20 |
| Fable 5.1 | $10 | $50 |
Caching, tools and output length can change the final bill. Check current Anthropic pricing before planning a budget.
Claude Max 20x is not a fifth model
Max 20x is a Claude usage tier, not a model. It does not belong in an “Opus versus Max” ranking. Our Claude Max 20x page explains higher usage capacity; the Claude page presents the assistant within Rankerfox. An Anthropic release does not, on its own, prove that every version named here is already selectable through Rankerfox. Check your session's model picker.
To compare Claude with other assistants in the catalog, see Rankerfox AI tools and our GPT-6 model guide.
A practical selection method
- Try Sonnet on three real tasks: easy, medium and difficult.
- Use Haiku for repeatable work you can verify.
- Compare Opus and Fable on hard cases with identical files, instructions and success criteria.
- Track errors and human rework, not just the speed of the first answer.
Frequently asked questions
Did Opus 5.5 replace Sonnet 5?
No. Opus is aimed at harder tasks; Sonnet remains a versatile and cheaper API option.
Are Sonnet 5.5 and Haiku 5.5 available already?
As of September 27, 2026, Anthropic describes them as forthcoming. This guide does not present them as available.
Is Fable 5.1 broadly available?
Anthropic states broad availability for Fable 5.1. Do not confuse it with Mythos 5.1, whose access is restricted to vetted organizations.
Official sources
Versions and prices checked on September 27, 2026: