# Which Claude model should you use? Haiku 5.5, Sonnet 5.5, Opus 5.5 or Fable 5.1

Canonical: https://theagenticweekly.com/guides/which-claude-model-should-i-use · Last verified: 2026-10-26 · Published: 2026-10-26 · Author: Agentic Weekly (operated independently from Texas, US) · Versions covered: Claude Fable 5.1, Opus 5.5, Sonnet 5.5 and Haiku 5.5 as listed on Anthropic's models overview, read 2026-10-26 · Evidence: Reported (not run by us): Anthropic's docs plus our editorial judgement · Tools: claude-code

Checked 2026-10-26 by Agentic Weekly's editorial process: vendor docs re-read.

> Anthropic's own advice is to start with Claude Opus 5.5 ($4 input, $20 output per million tokens) for most work, move to Sonnet 5.5 ($2/$10) for cheaper everyday coding, use Haiku 5.5 (from $0.10/$0.50) for subagents, and keep Fable 5.1 ($10/$50) for demanding reasoning. Verified 2026-10-26; we have not run these models.

## Quick chooser by task

The "start with" column follows Anthropic's [choosing-a-model guide](https://platform.claude.com/docs/en/about-claude/models/choosing-a-model) and [Haiku 5.5 announcement](https://www.anthropic.com/claude-haiku-5-5). The "move up" and "move down" columns are our editorial reading of the same pages, not test results.

Table: Which Claude model to start with, by task (Anthropic guidance plus our editorial judgement, read 2026-10-26)

| Task | Start with | Move up if | Move down if |
|---|---|---|---|
| Most workloads, if you are unsure | [Claude Opus 5.5](https://theagenticweekly.com/models/claude-opus-5-5): Anthropic says to start here for most workloads | Your evals at higher effort still fall short: try Fable 5.1 | Quality is already well above what you need: try Sonnet 5.5 |
| Everyday coding, agents and enterprise workloads at lower cost | [Claude Sonnet 5.5](https://theagenticweekly.com/models/claude-sonnet-5-5): Anthropic calls it the best combination of speed and intelligence | Complex multi-hour agentic coding or large refactors: Opus 5.5 | The task is narrow and high-volume: Haiku 5.5 |
| Long agent runs and large refactors | Opus 5.5: Anthropic lists multi-hour autonomous coding agents and large-scale refactoring | Sessions that run for hours or deep multistep research: Fable 5.1 | Work is well scoped and short: Sonnet 5.5 |
| The hardest reasoning and long-horizon work | [Claude Fable 5.1](https://theagenticweekly.com/models/claude-fable-5-1): Anthropic's most capable model open to all customers | Nothing above it is open to everyone | Opus 5.5 at higher effort first; Anthropic says to move to Fable if that falls short |
| Writing and knowledge work | Opus 5.5 or Sonnet 5.5; Anthropic lists content creation under Sonnet 5.5 and knowledge work under Opus 5.5 | Quality matters more than cost: Opus 5.5 or Fable 5.1 | Drafts and summaries at volume: Haiku 5.5 |
| Extraction, classification, routing | [Claude Haiku 5.5](https://theagenticweekly.com/models/claude-haiku-5-5): built for high-volume, latency-sensitive work | The task needs judgement across many files: Sonnet 5.5 | Already the cheapest Claude model |
| Subagents and compaction | Haiku 5.5: Anthropic says it pairs well with Opus 5.5 and Sonnet 5.5 as a subagent on coding work | The subagent must do complex coding itself: Sonnet 5.5 | Not applicable |

## Price and context at a glance

Table: Claude models: price, context and latency from Anthropic's models overview, read 2026-10-26 (US dollars per million tokens)

| Model | Input | Output | Context | Latency (Anthropic) | Default effort | API id |
|---|---|---|---|---|---|---|
| Claude Fable 5.1 | $10 | $50 | 1M tokens | Slower | high | `claude-fable-5-1` |
| Claude Opus 5.5 | $4 | $20 | 1M tokens | Moderate | medium | `claude-opus-5-5` |
| Claude Sonnet 5.5 | $2 | $10 | 1M tokens | Fast | high | `claude-sonnet-5-5` |
| Claude Haiku 5.5 | $0.10 up to 100K-token prompts, $0.50 above | $0.50 up to 100K-token prompts, $2.50 above | 1M tokens | Fastest | medium | `claude-haiku-5-5` |

All four list 128K maximum output and a June 2026 knowledge cutoff on that page. Cache-read prices differ: Opus 5.5 $0.20 and Sonnet 5.5 $0.10 per million tokens (Anthropic's [Opus 5.5](https://www.anthropic.com/news/claude-opus-5-5) and [Haiku 5.5](https://www.anthropic.com/claude-haiku-5-5) posts). Haiku 5.5 is the only one priced by prompt length; for the others Anthropic's pricing page says the full 1M context is included at standard pricing. See [Anthropic pricing](https://platform.claude.com/docs/en/about-claude/pricing) for batch discounts and caching.

## When Sonnet 5.5 is enough

Sonnet 5.5 costs half of Opus 5.5 per token and Anthropic's models overview calls it "the best combination of speed and intelligence" and lists code generation, data analysis, content creation, visual understanding and agentic tool use as its fit. Anthropic's Haiku post says it cut Sonnet 5.5's cache-read price by 50% to $0.10 per million tokens, which it says lowers the cost of most agentic work on Sonnet 5.5 by around 20%. If your task passes your own check on Sonnet 5.5, that is a sensible reason to stay on the cheaper model.

## When to pay for Opus 5.5

Anthropic's models overview says to start with Opus 5.5 for most workloads and describes it as built for long-running agentic coding and knowledge work. Its launch post claims it costs 40% less to run than Opus 5 on typical workloads; that is a vendor claim about its own previous model, not a comparison with other vendors. Anthropic also says that Opus 5.5 and Haiku 5.5 default to medium effort while Sonnet 5.5 and Fable 5.1 default to high, and that "Tuning effort is often a better lever than switching models."

## When Haiku 5.5 is the right worker

Anthropic positions Haiku 5.5 for quick, repetitive, high-volume work such as summaries, compaction, database queries and classification, and for speed-sensitive jobs like live support and browser use. Its own post is careful about limits: "Sonnet 5.5 and Opus 5.5 remain better choices for complex agentic coding tasks", while Haiku 5.5 is best suited to narrowly scoped tasks like compaction, summarization or subagent work. Customer quotes in that post are Anthropic-selected and we have not verified them.

## Where does Fable 5.1 fit?

Only from Anthropic's pages: Fable 5.1 is the highest-priced of these four at $10/$50, described as for demanding reasoning and long-horizon agentic work. Anthropic says to move to it when your evals on Opus 5.5 at xhigh or max effort still fall short, and that it extends Fable 5 with stronger long-running agentic coding, knowledge work and research at the same prices. We list a release-date discrepancy between sources on the [Fable 5.1 page](https://theagenticweekly.com/models/claude-fable-5-1) rather than guess here.

## Using these in Claude Code

Claude Code's docs say that on the Anthropic API the opus, sonnet and haiku aliases resolve to Opus 5.5, Sonnet 5.5 and Haiku 5.5, and that the fable alias resolves to Fable 5.1. On other providers the aliases can point to older models (for example the sonnet alias resolves to Sonnet 4.5 on Amazon Bedrock and Google Cloud's Agent Platform), so check your provider's row in that table. They also describe an opusplan mode that uses Opus during plan mode and then switches to Sonnet for execution. Start from [Claude Code](https://theagenticweekly.com/tools/claude-code), and see [GPT-6.1 Terra vs Claude Opus 5.5](https://theagenticweekly.com/compare/gpt-6-1-terra-vs-claude-opus-5-5) if you are weighing a non-Claude option. For model rankings on coding benchmarks, see [best LLM for coding](https://theagenticweekly.com/best/llm-for-coding).

## What we tested

Nothing: we have not run these four models for this page. Every price, limit and positioning statement is Anthropic's, read from its docs and posts on 2026-10-26. The advice to move up or down is editorial judgement: the reliable way to choose is an eval on your own prompts and data, which is also Anthropic's advice.

## Related tools

- [Claude Code](https://theagenticweekly.com/tools/claude-code): Update now if you use the sandbox or run Claude Code on a cloud provider; skip if you wanted flashy new features, this is a hardening release. Tested (smoke test, 2026-10-25, local Qwen2.5-3B-Instruct, not vendor models).

## FAQ

### Which Claude model is best for coding?

Anthropic lists Opus 5.5 for complex agentic coding and Sonnet 5.5 for everyday coding. Anthropic's Haiku post says Sonnet 5.5 and Opus 5.5 remain the better choices for complex agentic coding. For benchmark numbers see our best LLM for coding page; we have not run the models ourselves.

### Which Claude model is best for writing, research and planning?

Anthropic does not rank them by those tasks. Its guide lists content creation for Sonnet 5.5, knowledge work and complex enterprise work for Opus 5.5, and multistep deep research for Fable 5.1. Start with Opus 5.5 or Sonnet 5.5 and run your own prompts.

### Is Haiku 5.5 good enough for subagents?

Anthropic says it pairs well with Opus 5.5 and Sonnet 5.5 as a subagent on coding work, and is best suited to narrowly scoped tasks such as compaction, summarization and subagent work.

### Should I use Opus 5.5 or Fable 5.1?

Anthropic says to start with Opus 5.5 and move to Fable 5.1 if your evals at xhigh or max effort still fall short on demanding reasoning or long-horizon agentic work. Fable 5.1 costs $10/$50 against $4/$20.

### How much cheaper is Sonnet 5.5 than Opus 5.5?

Half per token on list price: $2 input and $10 output against $4 and $20 per million tokens, per Anthropic's models overview on 2026-10-26. Real bills also depend on how many tokens each model uses for your task, so run your own prompts before assuming a saving.

### Have you tested these Claude models?

No. We have not run Opus 5.5, Sonnet 5.5, Haiku 5.5 or Fable 5.1 for this page. Prices, limits and positioning are Anthropic's own statements, read on 2026-10-26, and the advice to move up or down is editorial judgement.

## Sources

- [Anthropic: models overview](https://platform.claude.com/docs/en/about-claude/models/overview) (fetched 2026-10-26)
- [Anthropic: choosing the right model](https://platform.claude.com/docs/en/about-claude/models/choosing-a-model) (fetched 2026-10-26)
- [Anthropic: optimizing for cost and intelligence](https://platform.claude.com/docs/en/about-claude/models/optimizing-for-cost-and-intelligence) (fetched 2026-10-26)
- [Anthropic: Introducing Claude Haiku 5.5](https://www.anthropic.com/claude-haiku-5-5) (fetched 2026-10-26)
- [Anthropic: Introducing Claude Opus 5.5](https://www.anthropic.com/news/claude-opus-5-5) (fetched 2026-10-26)
- [Anthropic: Claude Opus 5.5 model page](https://platform.claude.com/docs/en/models/opus-5-5/overview) (fetched 2026-10-26)
- [Anthropic: pricing](https://platform.claude.com/docs/en/about-claude/pricing) (fetched 2026-10-26)
- [Claude Code docs: model configuration](https://code.claude.com/docs/en/model-config) (fetched 2026-10-26)

## Related

- [Claude Opus 5.5: facts and sources](https://theagenticweekly.com/models/claude-opus-5-5)
- [Claude Sonnet 5.5: facts and sources](https://theagenticweekly.com/models/claude-sonnet-5-5)
- [Claude Haiku 5.5: facts and sources](https://theagenticweekly.com/models/claude-haiku-5-5)
- [Claude Fable 5.1: facts and sources](https://theagenticweekly.com/models/claude-fable-5-1)
- [GPT-6.1 Terra vs Claude Opus 5.5](https://theagenticweekly.com/compare/gpt-6-1-terra-vs-claude-opus-5-5)
- [Best LLM for coding](https://theagenticweekly.com/best/llm-for-coding)
- [Claude Code](https://theagenticweekly.com/tools/claude-code)
- [Is Claude Opus 5.5 free or paid?](https://theagenticweekly.com/guides/claude-opus-5-5-free-or-paid)
- [Best model for OpenCode, Cline and Claude Code](https://theagenticweekly.com/guides/best-model-for-opencode-cline-claude-code)

## Changelog

- 2026-10-26: First published. Anthropic's models overview, choosing-a-model guide, pricing page, Opus 5.5 and Haiku 5.5 posts and Claude Code model docs read on this date; nothing was run.

## How to cite

Agentic Weekly, "Which Claude model should you use? Haiku 5.5, Sonnet 5.5, Opus 5.5 or Fable 5.1", last updated 2026-10-26, https://theagenticweekly.com/guides/which-claude-model-should-i-use