Claude Sonnet 5.5 vs Opus 5.5: Coding, writing and cost

Fact-checked: October 23, 2026.

Start by testing Claude Sonnet 5.5 for routine coding, writing and everyday usage if cost matters. Test Claude Opus 5.5 on the same brief when the first answer misses your requirements, or when a small improvement would justify the extra spend.

That is a candidate-to-test recommendation based on price, not proof that Sonnet is good enough or Opus is better. We did not run a controlled quality or latency benchmark for this article. A higher token rate does not establish a better answer.

Quick decision: what should you test first?

For coding, do not confuse a plausible patch with a verified fix. For writing, do not confuse a polished paragraph with a supported claim. Keep whichever result meets your criteria with less total cost and rework. Either model can win your test, and both can fail.

Capabilities and limits in magicdoor.ai

These are shared workspace capabilities, not evidence of equal answer quality.

Both can help explain code or propose changes without executing it. Hosted execution is separate: it runs in Anthropic's isolated container, not your computer, editor or local repository. Upload only files you are permitted to share. Execute and review project-specific tests in your own environment before accepting a change.

Anthropic's model overview lists 1M context and up to 128K output for both models. Those are vendor limits, not a promise that every file fits or every answer reaches that length. Magicdoor also uses context management, and attachments, history and tool messages consume context. For a fair test, keep the input small enough to avoid different truncation or compaction between runs.

Pricing: compare tokens, then compare the bill

Current magicdoor.ai USD rates per 1 million tokens, checked against the model registry and customer cost calculation:

Opus has twice the uncached input, output and cache-write rates. Cache reads cost the same, so a cache-heavy request is not necessarily twice the total price. Different answer lengths can also change the ratio. Neither model currently has a long-context price multiplier in Magicdoor's rate card.

Caching is conditional. As Anthropic's prompt-caching documentation explains, hits require an eligible matching prefix within its lifetime, and minimum cacheable lengths vary by model. Repeating a short prompt or changing models does not guarantee a hit or a shared cache. These are Magicdoor's customer rates, not a copy of Anthropic's direct API tariff. Magicdoor's standard Claude route uses ephemeral caching with the default 5-minute lifetime. The 1-hour row explains how reported 1-hour writes are priced, not a selectable lifetime promised in chat.

Realistic text-only quote examples

These are equal-token illustrations from the production cost function, not measured requests. Input includes any resent conversation history. Output is a billing token count, not a word count; record all reported output, including reasoning usage where applicable.

For example, the Sonnet code-review quote is 10,000 / 1,000,000 × $2 + 2,000 / 1,000,000 × $10 = $0.040. Running that equal-token request once on each model would total $0.120, not the price of just one answer.

The cache-read example assumes the prefix was already written; its earlier write charge is not included. Cache writes replace the base input rate for those tokens, rather than being free. Actual usage can differ from these examples, especially in multi-step tool runs.

These examples exclude subscription fees and separate tool charges. For both Claude models, Magicdoor currently records about $0.00417 per turn when code executes or a data file is uploaded, in addition to token usage. Search or other tools can add their own usage. Check recorded costs rather than treating a text-only quote as an all-in tool quote. See current plans and the model-cost guide; this comparison does not assume a particular plan's included balance.

A fair Sonnet vs Opus comparison checklist

Use two fresh chats for independent answers. Switching models and asking the second to critique the first can be useful, but it measures a revision workflow with extra context, not a head-to-head comparison.

1. Write the pass criteria first. For code: required behavior, tests, edge cases and allowed dependencies. For writing: audience, source facts, voice, length and forbidden claims.
2. Hold the brief constant. Paste the same prompt and attach the same permitted files in each fresh chat. Select Sonnet 5.5 manually in one and Opus 5.5 in the other, rather than Auto. Do not show either model the other's answer.
3. Match settings and tools where possible. Record available reasoning settings and tool access. For a text-only test, ask both not to use tools and verify whether they did. For an execution test, use the same data and record tool activity. If settings differ, disclose that limitation.
4. Score before choosing. Hide model labels if practical. Mark each result pass or fail for correctness, completeness, instruction-following and source fidelity. Then record minutes of human repair. For code, run the same tests; for writing, check each factual claim against the supplied sources.
5. Record real usage separately. Note input, output, cache usage, tool charges and total recorded cost for each answer. Time both runs if latency matters, but one timing is not a speed benchmark. A second answer is another billed request, not a free comparison.
6. Repeat on representative work. Try a few tasks you actually do, within your budget. A single impressive answer is not a universal ranking. Stop if both fail, improve the brief, and restart both on that revised input.

Copy this same-brief prompt

Task: [one concrete coding or writing job]
Audience or environment: [reader, language, framework and versions]
Source material: [paste the same permitted text or attach the same files]
Required output: [format and length]
Must pass:
1. [observable acceptance criterion]
2. [observable acceptance criterion]
3. [edge case or source-fidelity requirement]
Constraints: [dependencies, tone, scope and tool policy]

Work only from this brief. State assumptions and missing information.
Do not invent test results, citations or facts. If proposing code, include
how to verify it and distinguish tests you ran from tests you recommend.
For writing, flag claims the supplied sources do not support.

Keep a simple worksheet: task, model, settings, tools used, pass/fail criteria, factual errors, repair minutes, recorded tokens/cache, total cost and preferred result. If Opus saves enough rework on your difficult tasks, use it there. If Sonnet meets the same bar for less, keep it. Do not pay for a model name alone.

For a broader coding evaluation framework, use the AI coding guide. This page owns the two-Claude decision, not a ranking of every coding model.

Try the same brief in chat

magicdoor.ai publishes this comparison and sells access to both models, so we have a commercial interest in that choice. The recommendations above are editorial starting points, not results from a paid or independent benchmark. Anthropic describes Opus as a model for long-running agentic coding and knowledge work; that vendor positioning is not a measured win on your task.

Compare Claude models in chat

This opens chat, or sign-in if you are signed out. It does not preselect either model or create a comparison. After signing in, choose each model manually in separate fresh chats. Opus requires a subscription, and both answers consume usage balance. For general model-choice advice, see the model selection guide.

Sources checked October 23, 2026: Anthropic's model overview for vendor specs and positioning, and prompt caching for cache behavior. Magicdoor's model registry, token-cost calculator and Claude route govern the workspace prices, access and tools described here. No quality or speed superiority claim is inferred from those sources.

FAQ

Should I use Claude Sonnet 5.5 or Opus 5.5 for coding?

Test Sonnet 5.5 first when cost matters, then test Opus 5.5 on the same brief if the result misses your acceptance criteria. Run the proposed tests yourself. This is a cost-led starting recommendation, not a measured coding-quality winner.

Which Claude model should I use for writing?

Start by testing Sonnet 5.5 for drafts and edits. For an important document, compare both models against the same sources, audience, tone and word limit. Choose on factual accuracy and editing effort, not the model name or price.

Is Opus 5.5 always twice the price of Sonnet 5.5?

No. Uncached input, output and cache-write rates are twice as high, but both models charge $0.20 per million cache-read tokens on magicdoor.ai. Actual totals depend on output length, cache hits, conversation history and tools.

Does switching models in one conversation make a fair comparison?

Not if the second model sees the first answer. That tests a revision workflow, not independent answers. Use two fresh chats with the same brief and attachments, then score the answers against criteria written before testing.

Can both models run code on magicdoor.ai?

Both support hosted code execution in Anthropic's isolated container. This is not an agent with access to your local repository. Execution or data-file upload adds a separate usage charge; text-only quote examples exclude it.

Do I need separate Claude subscriptions?

You do not need separate Anthropic subscriptions to use these models through magicdoor.ai. Opus 5.5 is subscriber-only here, and model usage is billed against your available balance. Check the pricing page for current plan terms.