Claude Sonnet 5.5 vs Claude Opus 5.5: Is the Cheaper Model Enough?
Model Comparison
Claude Sonnet 5.5 costs half as much as Claude Opus 5.5 and, on Anthropic’s launch benchmarks, lands within two points of it on knowledge work and computer use. Here’s where the gap is real, where it isn’t, and which one to pick.
Quick answer: Claude Sonnet 5.5 ($2/$10) is the better value for everyday work and high-volume agents: it nearly ties Claude Opus 5.5 ($4/$20) on GDPval-AA v2.1 (1,844 vs 1,846) and OSWorld 2.1 (80.1% vs 81.8%) and is faster. Opus 5.5 is the safer pick for the hardest coding and reasoning — it leads by 8.2 points on FrontierCode — and it’s the model Anthropic recommends starting with.
Sonnet 5.5 vs Opus 5.5 at a Glance
| Dimension | Claude Sonnet 5.5 | Claude Opus 5.5 |
|---|---|---|
| Released | September 28, 2026 | September 22, 2026 |
| API model ID | claude-sonnet-5-5 | claude-opus-5-5 |
| Anthropic’s positioning | Best combination of speed and intelligence | Long-running agentic coding and knowledge work |
| Price / MTok (in / out) | $2 / $10 | $4 / $20 |
| Batch API | $1 / $5 | $2 / $10 |
| Cache reads / MTok | $0.20 | $0.20 |
| Cache writes (5m / 1h) | $2.50 / $4 | $5 / $8 |
| Fast mode | No | Yes — $8/$40, up to 2.5× speed |
| Latency | Fast | Moderate |
| Default effort (API) | high | medium |
| Thinking | Adaptive; between_tools turns off up-front thinking | Adaptive, always on |
| Context / max output | 1M / 128K | 1M / 128K |
| Knowledge cutoff | June 2026 | June 2026 |
| Claude Code | /model sonnet | Default model |
Benchmarks: Head to Head
From Anthropic’s Sonnet 5.5 launch table. Opus 5.5’s Terminal-Bench 4.0 score used xhigh effort; Sonnet 5.5’s FrontierCode score used max effort, which Anthropic notes scored lower than xhigh.
| Benchmark | Sonnet 5.5 | Opus 5.5 | Leader |
|---|---|---|---|
| Terminal-Bench 4.0 (agentic coding) | 70.6% | 66.4% | Sonnet 5.5 (+4.2) |
| GDPval-AA v2.1 (knowledge work, Elo) | 1,844 | 1,846 | Opus 5.5 (+2) |
| AA-Briefcase v1.1 (knowledge work, Elo) | 1,811 | 1,822 | Opus 5.5 (+11) |
| OSWorld 2.1 (computer use, partial credit) | 80.1% | 81.8% | Opus 5.5 (+1.7) |
| CursorBench 4.0 (agentic coding) | 55.5% | 57.8% | Opus 5.5 (+2.3) |
| Chartography (chart recognition, no tools) | 61.6% | 64.4% | Opus 5.5 (+2.8) |
| Humanity’s Last Exam (with tools) | 64.5% | 67.7% | Opus 5.5 (+3.2) |
| FrontierCode 1.1 Main (agentic coding) | 46.2% | 54.4% | Opus 5.5 (+8.2) |
Opus 5.5 leads on seven of eight rows, but on four of them — GDPval-AA, OSWorld, CursorBench, and Chartography — the margin is under three points. The two gaps that matter are FrontierCode, a hard agentic-coding benchmark where Opus 5.5 is 8.2 points ahead, and Humanity’s Last Exam. Sonnet 5.5’s one outright win, Terminal-Bench 4.0, is also its most striking — Sonnet 5 scored 10.3% on the same test. Anthropic adds that Sonnet 5.5’s GDPval-AA and AA-Briefcase runs hit a structured-outputs bug it expects understated the results.
Cost and Speed
Sonnet 5.5 is half Opus 5.5’s price on input, output, cache writes, and Batch; only cache reads cost the same ($0.20). It’s also the faster model — “Fast” latency against Opus 5.5’s “Moderate” — and Anthropic says it generates output more than 30% faster than Sonnet 5 while using fewer tokens and tool calls per task.
Opus 5.5 narrows the gap in two ways: it defaults to medium effort on the API, which keeps token use down, and it offers fast mode when latency matters more than price. For subscribers, the choice also affects usage limits — lighter models stretch your allowance further, which is why switching Claude Code to Sonnet 5.5 for routine work is a common tactic. See Claude Code pricing and usage limits, or model API spend in the cost estimator.
Other Differences
- Thinking control: Sonnet 5.5’s
between_toolssetting turns off up-front thinking for latency-sensitive apps. Opus 5.5’s thinking is always on. - Cybersecurity safeguards: higher-risk cyber tasks on Sonnet 5.5 fall back to Sonnet 5; on Opus 5.5, most cyber tasks route to Opus 4.8.
- Migration: both reject forced tool use, bind thinking blocks to the model and conversation, and no longer accept the
computer_20251124tool on the Claude API and Google Cloud. Sonnet 5.5 also changes advisor-tool pairings. - Data retention: both are available with zero data retention.
The Verdict
Choose Claude Sonnet 5.5 for everyday coding, writing, research, document and spreadsheet work, customer-facing apps, and high-volume agent pipelines. You give up little on most benchmarks and pay half as much, with faster responses.
Choose Claude Opus 5.5 for the hardest multi-step coding, long unsupervised agent runs, and research where a wrong answer is expensive. It’s Anthropic’s recommended default and Claude Code’s out-of-the-box model for good reason.
A practical pattern: start on Sonnet 5.5, and escalate to Opus 5.5 — or, for the very hardest work, Fable 5.1 — only for the tasks where your evals show it falling short. For the top of the range, see Opus 5.5 vs Fable 5.1.
Frequently Asked Questions
Is Claude Sonnet 5.5 as good as Opus 5.5?
Nearly, on many tasks. In Anthropic’s launch table Sonnet 5.5 is within three points of Opus 5.5 on four of eight benchmarks, including GDPval-AA v2.1 (1,844 vs 1,846) and OSWorld 2.1 (80.1% vs 81.8%), and ahead on Terminal-Bench 4.0 (70.6% vs 66.4%). Opus 5.5 leads clearly on FrontierCode (54.4% vs 46.2%) and Humanity’s Last Exam (67.7% vs 64.5%).
How much cheaper is Sonnet 5.5 than Opus 5.5?
Half the price: $2/$10 per million input/output tokens versus $4/$20, with Batch at $1/$5 versus $2/$10. Cache reads cost the same $0.20 per million tokens on both.
Which is faster, Sonnet 5.5 or Opus 5.5?
Sonnet 5.5. Anthropic lists it as Fast latency versus Moderate for Opus 5.5. Opus 5.5 offers a fast mode running up to 2.5 times faster, but at double its standard price ($8/$40).
Which model should I use in Claude Code?
Claude Code defaults to Opus 5.5. Many developers switch to Sonnet 5.5 with /model sonnet for routine edits to stretch their usage limits, and keep Opus 5.5 for complex multi-file work. Sonnet 5.5 needs Claude Code v2.1.284 or later.
Does Anthropic recommend Sonnet 5.5 or Opus 5.5?
Anthropic’s documentation says to start with Claude Opus 5.5 for most workloads, and describes Sonnet 5.5 as the best combination of speed and intelligence. In practice, Sonnet 5.5 is the cost-efficient choice when its benchmark results are close enough for your task.