The short version
A practical November 2026 comparison of Anthropic's Claude Opus 5.5 and Claude Sonnet 5.5: API and plan pricing, speed, benchmark results, and which model fits heavy agentic work versus high-volume daily tasks.
Summarize with AI
Editorial Disclosure & Affiliate Notice
This content is published for informational and educational purposes only. It is not intended as a substitute for professional, legal, financial, or medical advice. AIUnpacker is funded through clearly labeled sponsored articles and reviews, relevant paid link placements, and affiliate commissions where disclosed. Commercial partnerships help fund the free editorial library. Sponsored work is labeled, and a payment does not change the verdict.
- For educational purposes only. Nothing here should be taken as a guarantee, recommendation, or professional recommendation.
- AI-assisted editing. Drafts are produced with AI assistance and get a human pass before they go up.
- Opinions are our own. Also, we are not affiliated with most tools we cover unless explicitly stated.
- Information may be outdated. Verify pricing, features, and policies directly with the vendor.
- Last reviewed: . Published .
Read more on our About page, Terms and Editorial Policy.
Pick Claude Sonnet 5.5 for most of your daily work, and reach for Claude Opus 5.5 when a task is long, ambiguous, or expensive to get wrong. Sonnet 5.5 costs half as much per token, writes noticeably faster, and currently sits at #1 on the Vals Index, an independent benchmark of 34 frontier models. Opus 5.5, Anthropic’s strongest model, wins on judgment-heavy work: deep research, architecture decisions, multi-hour agentic jobs. Both share a 1-million-token context window and a June 2026 knowledge cutoff.
What are Claude Opus 5.5 and Sonnet 5.5?
They’re the two workhorse models in Anthropic’s current four-model lineup, both launched within a week of each other in September 2026.
Claude Opus 5.5 is the flagship, released September 22, 2026. Anthropic’s most capable Opus yet, performing at Fable 5.1’s level on most tasks while costing about 40% less to run than Opus 5. Model ID: claude-opus-5-5.
Claude Sonnet 5.5 followed on September 28, 2026, positioned as the best speed-and-intelligence mix: the model for well-scoped everyday work like bug fixes, documents, slides, and spreadsheets. It’s over 30% faster than Sonnet 5. Model ID: claude-sonnet-5-5.
Around them: Claude Fable 5.1, the premium model for the hardest long-horizon projects, and Claude Haiku 5.5 (October 7, 2026), ultra-cheap and built for classification, extraction, and routing. All four carry a 1M-token context window, 128K max output, and always-on adaptive thinking, per the Claude Platform model docs.
Claude Opus 5.5 vs Sonnet 5.5 at a glance
The verified spec sheet, from Anthropic’s docs and both launch pages:
| Claude Opus 5.5 | Claude Sonnet 5.5 | |
|---|---|---|
| Released | September 22, 2026 | September 28, 2026 |
| Best for | Long agentic jobs, judgment-heavy work | Everyday high-volume tasks |
| Context window | 1M tokens | 1M tokens |
| Max output | 128K tokens | 128K tokens |
| Knowledge cutoff | June 2026 | June 2026 |
| API price (input/output per MTok) | $4 / $20 | $2 / $10 |
| Cache read / write per MTok | $0.20 / $5.00 | $0.10 / $2.50 |
| Fast mode (up to 2.5x speed) | $8 / $40 | Not offered |
| Latency (per docs) | Moderate | Fast |
| Default effort on the API | Medium | High |
| Terminal-Bench 4.0 | 66.4% (xhigh) | 70.6% (max) |
| FrontierCode v1.1 Main | 54.4% | 52.1% (xhigh) |
| GDPval-AA v2.1 Elo | 1846 | 1844 |
| Humanity’s Last Exam (with tools) | 67.7% | 64.5% |
| Plan access | Paid plans only | Every plan, including Free |
One honest note: Sonnet’s 70.6% Terminal-Bench run happened at max effort while Opus’s 66.4% was at xhigh: why that matters in a moment.
How big is the real capability gap between Opus 5.5 and Sonnet 5.5?
Smaller than the price gap, but real, and it shows up exactly when tasks get long and vague.
Anthropic’s own evals put Opus ahead on most knowledge and agentic benchmarks: most strikingly, Opus 5.5 passed a hard research-report quality bar 16 times out of 18, while Fable 5.1 and Opus 5 passed zero. Sonnet 5.5 sits close behind on GDPval-AA (1844 vs 1846 Elo) and further back on FrontierCode (52.1% vs 54.4%) and Humanity’s Last Exam (64.5% vs 67.7%).
Third-party labs mostly agree Opus leads at the ceiling. Artificial Analysis’s head-to-head comparison scores Opus 5.5 at 59 on its intelligence index at max effort versus 55 for Sonnet 5.5, with OpenAI’s GPT-6 Astra (max) at 63 and Google’s Gemini 4 Carbon at 59-60.
But the twist that changes the decision for most people: the Vals Index currently ranks Sonnet 5.5 #1 of 34 models at 70.85%: ahead of Gemini 4 Carbon (70.45%) and Opus 5.5 (70.18%, third) as of November 5, 2026. Sonnet 5.5 also beats GPT-6 Astra on 18 of 24 shared benchmarks.
Sonnet 5.5 went from 10.3% to 70.6% on Terminal-Bench 4.0 in one generation: a jump large enough that, at matched effort settings, Opus 5.5 still leads (66.4% vs roughly 61.5%), but your default no longer feels like a downgrade.
The honest summary: at matched effort Opus wins; at default settings it’s nearly a tie, and Sonnet costs half as much.
The effort-setting trap
Effort levels control how many thinking tokens and tool calls a Claude model burns before answering (low through max) and they’re why naive comparisons mislead. Opus 5.5 defaults to medium effort on the API; Sonnet 5.5 defaults to high. Artificial Analysis’s effort-by-effort data shows Sonnet 5.5 at high effort scoring 50 on its index versus 42 for Opus 5.5 at medium, while costing $1.64 per task versus $2.45. Push both to max effort and per-task costs converge near $10.
Leave Opus at its default and you may pay more per token for worse measured performance than Sonnet 5.5 at its default. The premium only pays off when you let Opus work hard.
How much do Opus 5.5 and Sonnet 5.5 cost?
On the API, Sonnet 5.5 costs exactly half of Opus 5.5: $2 per million input tokens and $10 output, versus $4/$20. Cache reads are $0.10 versus $0.20 per million, cache writes $2.50 versus $5, batch requests 50% cheaper for both, per the model docs.
Per task, the gap depends on effort. Artificial Analysis measured Opus 5.5 at $0.98 per task at its default and Sonnet 5.5 at $0.51 at low effort; a myclaw.ai analysis costed a representative 200K-input-plus-10K-output request at $0.50 on Sonnet versus $1.00 on Opus before caching. At max effort, both land near $10 per task. Sonnet’s price advantage disappears there.
Two extra levers worth knowing:
- Fast mode (Opus 5.5 only) buys up to 2.5x output speed for 2x the tokens: $8/$40. Anthropic’s pricing docs note it can miss the prompt cache, so don’t blanket-enable it.
- Anthropic’s own claims: Sonnet 5.5 runs up to 30% cheaper per task than Sonnet 5, and Opus 5.5 cut Opus 5’s costs about 40% on typical workloads.
Which Claude plan includes Opus 5.5 and Sonnet 5.5?
Sonnet 5.5 is on every plan, including Free. Opus 5.5 requires a paid plan. That’s the short answer, straight from claude.com/pricing as of November 2026.
The full picture:
- Free ($0): Sonnet 5.5 and Haiku 5.5 only, with limited usage every 5 hours and every week.
- Pro ($20/month, or $17/month billed annually): Opus 5.5 and Sonnet 5.5, plus Claude Code, the Research feature, and Projects. Fable 5.1 is available via usage credits.
- Max ($100/month): 5x Pro usage per 5-hour window and weekly, Fable 5.1 up to 50% of your weekly limit, plus $100 in monthly API credits.
- Ultra ($200/month): 10x Pro’s weekly usage with no 5-hour limit for verified accounts, Fable 5.1 up to 50% of weekly usage, and $200 in monthly API credits.
Usage is a shared pool across web, desktop, mobile, and Claude Code, and it drains faster on Opus than Sonnet. Anthropic prices access by model, then by volume.
One feature blurs the choice entirely: the Research feature (paid plans only) always runs on Opus 5.5 (falling back to Opus 4.8 when needed) regardless of your chat’s model, so a Pro subscriber on Sonnet still gets Opus-grade deep research on request.
As for defaults: available coverage indicates Sonnet 5.5 is the chat default for Free and Pro users, with Opus a deliberate switch in the model picker. In Claude Code, the model configuration docs say default currently resolves to Opus 5.5 on paid plans and the API, and the opusplan setting pairs both. Opus for planning, Sonnet for execution.
When is Claude Opus 5.5 worth the premium?
When the cost of being wrong exceeds the cost of the tokens. The verified examples from Anthropic’s launch page:
- Long agentic coding: a 680,000-line migration finished in under a day; a 200,000-line codebase audit-and-fix run in under 3 hours, where Opus 5 needed 20+ hours.
- Knowledge work: 16 of 18 hard research reports passed a quality bar both Fable 5.1 and Opus 5 failed; a merger analysis took 63 minutes versus 93 for Opus 5, at half the cost.
The docs do not state this. Opus 5.5’s sweet spot is tasks with vague success criteria, where the model decides what “done” means. Crisp-answer benchmarks compress the gap; open-ended judgment doesn’t.
When is Claude Sonnet 5.5 the smarter pick?
For everything high-volume, well-scoped, or verifiable, which is most work. If a task has a clear definition of done (a tested bug fix, a deck from an outline, a spot-checkable summary), Sonnet 5.5 does it faster and cheaper, and Anthropic’s positioning calls it the best speed/intelligence mix in the family.
The speed numbers hold up across sources: Artificial Analysis measured about 151 tokens per second for Sonnet 5.5 at max effort versus roughly 116 for Opus, and OpenRouter’s stats show medians near 108 vs 72.
Three everyday scenarios where Sonnet 5.5 is the clear call:
- Writing and editing: community writing benchmarks rank Sonnet 5.5 just behind Opus at less than half the cost, and for drafts nobody but you will read, that trade is easy.
- Coding on a budget: its 70.6% Terminal-Bench 4.0 score at max effort beats Opus 5’s 52.3%, and usage-limited developers stretch their allowance much further.
- High-volume pipelines: classification, extraction, and batch processing, where Sonnet 5.5 at low effort measured $0.51 per task: half of Opus at its default.
How to decide in five steps
- Check your plan. Free means Sonnet 5.5, full stop. Pro or higher means you can use both.
- Start your default on Sonnet 5.5. Fast, cheap, and ranked #1 on the Vals Index: a strong baseline.
- Watch for the signals that a task needs Opus. Long runtimes, ambiguity about what “done” means, high cost of an error, or research that needs real sourcing.
- Match effort to task. Switching to Opus only pays at high effort or above, at medium it can underperform cheaper Sonnet configs. Don’t park Sonnet at max effort either; per-task costs converge with Opus there.
- Use both where they’re strongest. In Claude Code,
opusplanautomates the split. Opus plans, Sonnet executes. On the API, Opus reviews, Sonnet works, switching at task boundaries.
Where Fable 5.1 and Haiku 5.5 fit in the lineup
Fable 5.1 is the step above both: $10/$50 per million tokens, rated for “demanding reasoning and long-horizon agentic work” per the model docs. Unless you’re on Max or Ultra (capped at 50% of weekly usage) or burn Pro usage credits, you’ll rarely touch it. Opus 5.5 already matches it on most tasks at 60% of the price. Haiku 5.5 (October 7, 2026, from $0.10/$0.50) is the volume model: support triage, document extraction, routing.
Limitations and gotchas worth knowing
A few things the spec sheet won’t tell you:
- Usage limits bite harder on Opus. Every plan pools usage across models and surfaces; Opus sessions drain allowances faster. Ultra removes the 5-hour cap for verified accounts; Max and Pro don’t.
- The effort mismatch skews public benchmarks. Sonnet’s headline Terminal-Bench win came at max effort; at matched settings Opus leads. Check the annotation before quoting any number, including the ones in this article.
- Thinking can’t be turned off. All 5.5-family models run adaptive thinking permanently.
- Opus 5.5 can silently swap to Opus 4.8. When the safety classifier flags a request on Anthropic’s own products, it falls back to Opus 4.8 and returns a normal response, per the platform docs on refusals and fallback.
- Fast mode can miss the prompt cache, eroding its savings on cache-heavy workloads.
- Benchmarks shift monthly. The Vals snapshot cited above is from November 5, 2026; re-check rankings before locking in an API budget.
What to do
Stay on Sonnet 5.5 as the default; add Opus 5.5 for anything that runs longer than a coffee break or involves decisions with real consequences. API builders: Sonnet for the hot path, Opus at high effort for planning and review, Haiku for cheap classification. If Pro limits keep interrupting you at 2pm, the realistic fix is Max ($100/month), not a model switch.
FAQ
Is Claude Opus 5.5 better than Claude Sonnet 5.5?
On raw capability, yes. Opus 5.5 is Anthropic’s strongest model, leading Terminal-Bench 4.0, FrontierCode, and GDPval-AA, and scoring 59 versus Sonnet 5.5’s 55 on Artificial Analysis’s index at max effort. But Sonnet 5.5 tops the Vals Index at 70.85% versus Opus’s 70.18%. For most tasks, Sonnet’s speed and half price matter more than Opus’s headroom.
Which Claude model should I use for everyday work?
Sonnet 5.5. Anthropic positions it as the best speed-and-intelligence mix, it’s the default chat model for most Claude app users, and it’s cheap enough to run all day. Use it for email drafts, documents, spreadsheets, routine bug fixes, and summaries. Switch to Opus 5.5 when a task is ambiguous, multi-hour, or expensive to get wrong: architecture calls, sourced research, huge migrations.
How much do Claude Opus 5.5 and Sonnet 5.5 cost?
On the Claude API, per million tokens: Opus 5.5 is $4 input / $20 output; Sonnet 5.5 is $2 input / $10 output. Cache reads cost $0.20 (Opus) and $0.10 (Sonnet); batch requests are 50% cheaper. Opus 5.5’s fast mode costs $8/$40. In practice, Artificial Analysis measured $0.98 versus $0.51 per typical task at default settings, and roughly $10 per task for both at max effort.
Which Claude plan do I need to use Opus 5.5?
Any paid plan: Pro ($20/month, or $17/month billed annually), Max ($100/month, 5x Pro usage), or Ultra ($200/month, 10x Pro weekly usage with no 5-hour limit for verified accounts). Opus 5.5 is not available on Free. Anthropic also raised five-hour Opus limits on paid plans and added a savable rate-limit reset at launch.
Is Claude Sonnet 5.5 available on the free plan?
Yes. Sonnet 5.5 and Haiku 5.5 are the two models Free users can access, within the free tier’s 5-hour and weekly usage limits. Free users also get web search, file creation, Artifacts, and up to 5 Projects, but not Opus 5.5, Research, or Claude Code. Paid users can keep working past limits via usage credits at API rates.
Which model is faster, Opus 5.5 or Sonnet 5.5?
Sonnet 5.5. Anthropic’s docs rate Sonnet’s latency Fast versus Opus’s Moderate, and Sonnet 5.5 generates output over 30% faster than Sonnet 5. Artificial Analysis measured roughly 151 tokens per second for Sonnet at max effort versus about 116 for Opus. Opus offers a fast mode at 2.5x speed for double the token price, but Sonnet remains the faster, cheaper option.
What is Claude Opus 5.5 best used for?
Long, judgment-heavy work: agentic coding sessions that run for hours, codebase migrations and audits, architecture decisions, competitive or financial analysis, and research reports where quality decides the outcome. In Anthropic’s examples, Opus 5.5 completed a 680,000-line migration in under a day and a 200,000-line audit-and-fix job in under three hours, where Opus 5 needed over 20 hours.
Do I need Opus 5.5 for Claude Code?
No, but it’s the current default. Claude Code’s default model resolves to Opus 5.5 on paid plans and the API, and many developers run Sonnet 5.5 for execution to stretch their budget. The opusplan setting is a popular middle ground: Opus for planning, Sonnet for implementation. Sonnet 5.5’s Terminal-Bench 4.0 score (70.6% at max effort) makes it viable for most coding tasks.
What are the main alternatives to Opus 5.5 and Sonnet 5.5?
Within Anthropic’s lineup: Claude Fable 5.1 ($10/$50 per million tokens) for the hardest long-horizon work, and Claude Haiku 5.5 (from $0.10/$0.50) for high-volume classification and extraction. Outside Anthropic, OpenAI’s GPT-6 Astra and Google’s Gemini 4 Carbon are closest; Artificial Analysis ranks GPT-6 Astra (max) at 63 versus Opus 5.5’s 59, with Gemini 4 Carbon at 59-60.
Can I switch between Opus 5.5 and Sonnet 5.5 in one workflow?
Yes. In the Claude apps, change the model per chat from the picker; in Claude Code, switch with /model or set opusplan to combine both automatically. API developers pair them. Opus reviewing, Sonnet executing. Caveat: Anthropic notes Sonnet cannot carry forward Opus thinking blocks, so switch at task boundaries.
Sources
- Introducing Claude Opus 5.5: Anthropic
- Claude Sonnet 5.5 launch page: Anthropic
- Models overview: Claude Platform docs
- Pricing: Claude Platform docs
- Claude pricing plans: claude.com
- Claude Sonnet 5.5 vs Claude Opus 5.5: Artificial Analysis
- Claude Sonnet 5.5 model page: Vals AI
- Use Research on Claude: Claude Help Center
- Model configuration: Claude Code docs
- Sonnet 5.5 vs Opus 5.5: effort, cost per task: myclaw.ai
- Refusals and fallback: Claude Platform docs
- Claude Haiku 5.5: Anthropic
- Claude Fable product page. Anthropic
Weekly digest
Get our weekly AI digest
The latest AI tools, prompts, and insights — short, useful, every week.
AIUnpacker Editorial
Articles are written for a specific question. Sponsored work is labeled.
