Claude Opus 5.5 vs Opus 5: Should You Switch?
Compare launch claims, independent tests, developer reports, current rates, and a checklist for deciding whether Opus 5.5 fits your workload.
Updated September 25, 2026. This comparison separates Anthropic’s launch claims from independent evaluations and developer reports. The short answer: Opus 5.5 looks like a meaningful efficiency upgrade, but quality gains vary by task. The evidence supports a measured trial, not an automatic migration of every workflow.
Price and context at a glance
| Claude Opus 5 | Claude Opus 5.5 | |
|---|---|---|
| Input per 1M tokens | $5 | $4 |
| Output per 1M tokens | $25 | $20 |
| Context window | 1,000,000 tokens | 1,000,000 tokens |
| Maximum output | Check the API and account settings | 128,000 tokens in Anthropic’s model docs |
BazaarLink’s public model catalogue listed these standard input and output rates on September 25. They are each 20% lower for Opus 5.5, but that does not mean every task costs 20% less: prompt caching, output length, retries, and tool use change the total. Both models have a one-million-token context window, so capacity alone is not a reason to switch.
What Anthropic says changed
Anthropic announced Opus 5.5 on September 22, claiming about 40% lower cost on typical workloads, clearer writing, and a speed increase of more than 30%. Those are the maker’s claims, not a guarantee for an individual workflow. Its launch page reports 66.4% for Opus 5.5 versus 52.3% for Opus 5 on Terminal-Bench 4.0. The comparison used different reasoning-effort settings, and Anthropic cautions that benchmark margins do not translate directly into day-to-day gains. Anthropic announcement
The system card reports 91.2% versus 85.4% on valid ProgramBench samples, including tasks with context up to one million tokens. That is a positive signal on Anthropic’s long-context evaluation, but this is still an evaluation designed by Anthropic. A score cannot establish that a model will retain every project decision through a long conversation. Opus 5.5 system card
How does it feel in practice? Reviews and community reports
Coding and agentic work: efficient, with no universal quality winner. Artificial Analysis gave Opus 5.5 a 58 on its Intelligence Index at maximum effort and found it led six of ten evaluations. It did not lead AA-LCR long-context, CritPt, or GDP.pdf. That is a strong aggregate result, not a ranking for every software task. Artificial Analysis
SonarSource tested a fixed Java set with 544 executable HumanEval and MBPP tasks. Opus 5.5 passed 87.68%, compared with 88.6% for Opus 5. The newer model generated 27.5% less code and 40% fewer output tokens; the review also found fewer blocker-level findings, but higher bug density and more concurrency findings. In this test, concision and efficiency improved while functional pass rate did not. SonarSource evaluation
Endor Labs used Claude Code on security-fix tasks. Opus 5.5 scored 68.7% on functional correctness versus Opus 5 at 73.7%; with security requirements, the scores were 33.5% and 32.4%. The researchers also flagged 51 likely training-data recall shortcuts, so the benchmark has a contamination caveat. The result supports an efficiency case more clearly than a blanket quality claim. Endor Labs evaluation
Small developer experiments are encouraging but not decisive. A Qiita author ran 24 tasks across five configurations and three repetitions. All coding configurations passed hidden tests; on a harder reasoning subset, Opus 5.5 at high effort scored 24/27 versus Opus 5 at high effort with 21/27. The author built the tasks and harness, so treat this as a useful reproduction rather than a standardized leaderboard. Qiita test
A German developer’s 30-run experiment found that Opus 5 high, Opus 5.5 high, and Opus 5.5 medium all completed the selected tasks. The two Opus 5.5 configurations cost about 43% and 47% less than Opus 5 high in that run set. The author’s workload and settings may not match yours. rotecodefraktion test
There are counterexamples. Taiwan’s CyberQ reported roughly 70 API calls in a small test; on one short task, maximum effort cost much more than medium without a clear quality improvement. The author notes the limited sample, so this is a warning to measure effort settings rather than a broad cost estimate. CyberQ test
Writing and long context: promising scores, mixed user anecdotes. In Braintrust’s 175-task writing evaluation, Opus 5.5 scored 84.4% and ranked first in that suite. It met the requested length budget on only 72% of tasks, which matters if concise output is part of the brief. Braintrust writing evaluation
A Reddit discussion about long conversations is mixed: one user found the model usable around 700,000 tokens, while another reported verbosity, missed instructions, and forgotten decisions at roughly 800,000. These are personal observations without shared prompts or scoring. They are prompts for your own context-retention test, not proof of a general threshold. Community discussion
Who should try switching?
Opus 5.5 is a good candidate for a controlled trial if you use Opus 5 for multi-step coding, tool-assisted work, code review, or writing where fewer output tokens could reduce cost. It is especially worth measuring if Opus 5 currently accounts for substantial usage and you can replay representative tasks.
Keep Opus 5 for now, or limit the trial, if your workflow depends on a known prompt-and-tool combination that has not been tested with the new model. High-stakes fixes need executable tests or human review either way. Do not assume a one-million-token window guarantees perfect recall, or that a benchmark percentage predicts your project’s success rate.
A practical migration test
Choose 20–30 real tasks. Hold prompts, tools, reasoning effort, and pass criteria constant. Track task success, correction time, input and output tokens, retries, and total cost. Include at least a few long-context and failure-prone cases. Start with low-risk work, review the results, then expand only if your own data shows a useful gain.
Opus 5.5 appears more economical per listed token and can be more concise. Independent tests show both wins and regressions, while public developer samples remain small. Is it really that good? It looks good enough to test seriously; whether it is better for you depends on the tasks you actually run.
FAQ
Does Opus 5.5 have a larger context window than Opus 5?
No. Anthropic’s model documentation lists a one-million-token context window for both. The system card reports a higher score for Opus 5.5 on its long-context test, but real conversations can vary.
Is Opus 5.5 always 20% cheaper?
BazaarLink’s public catalogue lists input and output rates that are each 20% lower. Total task cost also depends on token volume, caching, retries, and tool use.
Should I move production work to Opus 5.5 now?
First replay representative tasks and compare success rate, correction time, and total cost. Expand gradually, with tests or human review for high-risk work.
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