Claude Opus vs Sonnet: Which Anthropic Model to Use in 2026

Short answer: Sonnet 5 is the daily workhorse at $2 per million input tokens and $10 per million output, the right model for most coding, writing and analysis. Opus 5.5 is the heavy-lift model at $4 input and $20 output, best for long agentic coding runs, complex refactors and hard reasoning. On Claude Pro you get both, so the choice matters most when you route API calls or hit your usage limits.

Anthropic replaced both models in 2026. Sonnet 5 shipped on June 30 as a drop-in upgrade for Sonnet 4.6, and Opus 5.5 followed on September 22. Opus 4.7 and Sonnet 4.6 are now listed as legacy models. The price ratio is simple: Opus costs exactly twice as much as Sonnet per token.

Quick comparison

Which model you actually access on Claude Pro

On Claude Pro, per the Claude pricing page:

• Default: Sonnet 5, which Anthropic makes the default on Free and Pro
• Selectable: Opus 5.5 and Haiku 4.5 from the model menu. Fable 5.1, Anthropic's most demanding reasoning model, is available through usage credits on Pro and at 50% of weekly limits on Max
• Limits: usage resets on a rolling five-hour session window, with weekly limits on top. Opus draws down your allowance faster than Sonnet

In practice, the shared usage pool binds before model availability does. If you bounce between Sonnet for normal work and Opus for hard problems, you hit limits faster than if you stayed on Sonnet.

When Sonnet 5 is the right pick

Anthropic describes Sonnet 5 as the best combination of speed and intelligence and says it delivers performance close to Opus 4.8 at lower prices. In other words, today's mid-tier model does what last season's flagship did.

Use Sonnet when:

• Writing: blog posts, emails, copy, documentation. Output quality is at Opus level for most of these tasks in our use.
• Daily coding: feature work, small refactors, debugging single files.
• Document analysis: PDFs, contracts and research papers. The 1M context window holds full documents.
• Customer support and Q&A: structured responses, factual queries, multi-turn conversations.
• Data extraction: pulling fields from unstructured text, JSON generation, summaries.

For API users, Sonnet costs half as much as Opus per token. At millions of tokens per day, that compounds fast.

When Opus 5.5 is worth the upgrade

Opus 5.5 is Anthropic's recommended starting model for most workloads and is built for long-running agentic coding and knowledge work. Anthropic says it performs at the level of Claude Fable 5.1 on most work while costing 40% less to run than Opus 5, and generates output more than 30% faster than Opus 5.

Use Opus when:

• Long agentic coding runs: Anthropic reports 66.4% on Terminal-Bench 4.0 and 57.8% on CursorBench 4.0 for Opus 5.5, ahead of every other model in its launch table.
• Multi-file refactoring: changes that must stay consistent across 10+ files.
• Computer use and automation: 81.8% on OSWorld 2.0 in Anthropic's table.
• Complex reasoning chains: technical specifications, multi-step research synthesis, 67.7% on Humanity's Last Exam.
• High-stakes writing: legal documents, executive briefs, anything where one error is unacceptable.

Anthropic does not publish a Sonnet 5 score on the same benchmarks, so there is no clean vendor number for the gap. Our experience: the difference is small on routine work and clear on long, multi-step tasks.

Cost analysis: real-world session pricing

For a typical heavy session (50,000 input tokens and 30,000 output tokens):

• Sonnet 5: 50K × $2 + 30K × $10 per million = $0.10 + $0.30 = $0.40
• Opus 5.5: 50K × $4 + 30K × $20 per million = $0.20 + $0.60 = $0.80

The 2x premium for Opus pays for itself if the output saves a few minutes of human time over Sonnet. For professional work, that bar is easy to clear. For high-volume automated work, the gap compounds.

Both models support batch processing at 50% off, and prompt caching cuts repeated input sharply: cache reads cost 10% of the base input price on Sonnet 5 and 5% on Opus 5.5. A team pushing 100M tokens a month through Opus without caching or batching pays several times what it would with both turned on.

Speed comparison

Anthropic rates Sonnet 5's latency as "Fast" and Opus 5.5's as "Moderate" relative to the current lineup. Opus 5.5 also defaults to medium effort on the API, where Sonnet 5 defaults to high, which narrows the practical gap on short prompts.

For tasks where you are watching the screen, Sonnet's speed advantage matters. For batch jobs or long autonomous runs, Opus's extra latency is irrelevant.

Routing strategy for API users

A pattern most teams converge on:

1. Default to Sonnet 5 for standard requests.
2. Route to Opus 5.5 only when:
   • The task touches more than 5 files of code
   • The run is a long autonomous agent task
   • A previous Sonnet attempt failed on multi-step reasoning
   • The output goes into a high-stakes artifact (legal, financial, critical engineering)

Some teams build this routing into their orchestration. Most use it informally: Sonnet by default, Opus when Sonnet fails.

Claude Pro vs Max for heavy users

If you hit Pro's session limits regularly, Claude Max starts from $100 a month and lets you choose 5x or 20x Pro usage per session, with higher output limits and priority access at busy times. Max is billed monthly only.

• Max 5x: right for professionals doing 4 to 6 hours of AI work a day
• Max 20x: right for power users whose work is AI-saturated

Every paid plan includes Claude Code, and it draws from the same usage pool as chat. For developers, that bundling is the main argument for Max over separate coding subscriptions. See our Claude Code vs Cursor and Claude vs ChatGPT for coding comparisons for the coding-specific breakdown.

For broader AI model comparisons, see our Claude vs ChatGPT general comparison and best AI tools for productivity roundup.

How Sonnet and Opus compare to ChatGPT and Gemini

Quick reference for the closest rivals to Sonnet 5 and Opus 5.5 (both with 1M-token windows), with prices verified on vendor pages as of September 2026:

Sources: OpenAI API pricing and Gemini API pricing. No model in this table has a 2M-token window. Sonnet 5 and GPT-6 Sol are priced identically, and Opus 5.5 costs 40% of GPT-6 Astra. On Anthropic's own launch table, Opus 5.5 leads GPT-6 Astra on Terminal-Bench 4.0 (66.4% vs 57.9%). The "best" model still depends on workload.

For broader tool comparisons across AI categories, Toolradar lists 9,000+ AI tools with verified pricing and AI-identified alternatives.

FAQ

The right Claude model is the cheapest one that meets your quality bar. For most users, that's Sonnet 5. Start your free 14-day Dupple X trial →