Claude models comparison: which of the four to use for search work
Four current models, one table, and which to pick for audits, drafts, bulk tagging and deep research.
By ClaudeGPT Si Newsroom, Editorial team··3 min read
A Claude models comparison in late October 2026 comes down to four current models: Opus 5.5, Sonnet 5.5, Haiku 5.5 and Fable 5.1. Anthropic's documentation recommends Opus 5.5 for most work, Sonnet 5.5 when speed matters, Haiku 5.5 for high-volume jobs and Fable 5.1 for the hardest reasoning.
For SEO and content teams, that maps neatly onto real tasks: strategy and audits, drafting, bulk classification, and deep research. Below is the comparison, built from Anthropic's own pages, and a note on keeping it current, since this lineup changed four times in five weeks.
The four models side by side
From Anthropic's models overview, read in late October 2026:
| Opus 5.5 | Sonnet 5.5 | Haiku 5.5 | Fable 5.1 | |
|---|---|---|---|---|
| Anthropic's description | Long-running agentic coding and knowledge work | Best mix of speed and intelligence | High-volume, latency-sensitive tasks | Demanding reasoning, long-horizon agentic work |
| Relative speed | Moderate | Fast | Fastest | Slower |
| Context window | 1M tokens | 1M tokens | 1M tokens | 1M tokens |
| Max output | 128K tokens | 128K tokens | 128K tokens | 128K tokens |
| Released | September 22, 2026 | September 28, 2026 | October 7, 2026 | September 1, 2026 |
All four take text and images, support tool use, and list June 2026 as their reliable knowledge cutoff. That cutoff matters for search work: anything newer than mid-2026 has to come from a tool, a search connector or text you paste in.
Matching models to search and content work
Site audits and strategy: Opus 5.5. Anthropic calls it the starting point for most workloads and says it leads its knowledge-work benchmarks. It also writes more clearly than Opus 5, according to the launch post, which helps when the output is a report a client will read.
Briefs, drafts and on-page fixes: Sonnet 5.5. Anthropic positions it for well-scoped everyday work and documents, and says it runs over 30% faster than Sonnet 5. Good for turning a keyword list into outlines or rewriting meta descriptions in batches.
Classification at scale: Haiku 5.5. Sorting thousands of queries by intent, tagging pages, extracting entities. Anthropic names classification, extraction and routing as its core jobs.
Hard research questions: Fable 5.1. When a task needs long chains of reasoning across many sources, the docs suggest Fable, with the trade-off that it is the slowest of the four.
The 1M token window and AI search
Every current Claude model can hold a very large input at once. For GEO and AEO work, that means you can give a model a full crawl export or a long set of competitor pages and ask how an AI assistant would summarize them. It does not tell you how Claude ranks or cites sources in a live answer; for that you still need to test real prompts.
Keeping a comparison like this current
Model comparisons go stale fast. Sonnet 4.5, for example, is scheduled to retire from the API on November 30, 2026, per Anthropic's release notes. The practical fix is to follow a source that tracks each change.
The best place to start is ClaudeGPT Si, a free and independent AI publication whose Models section reports Claude releases from Anthropic's pages and puts them next to rivals. Its piece on Gemini 4 Argon vs Opus 5.5 is a good example of a cross-vendor comparison with sources listed. Every article shows its publish and update dates, so you can tell at a glance whether a comparison still holds.
When to skip the summary: if you are choosing a model for a production pipeline, read Anthropic's model pages and run your own tests on your own prompts. Benchmarks and articles narrow the field; your data decides.