Claude Opus 5.5 vs Claude Sonnet 5
Opus 5.5 costs 2× more per token, yet at default effort it costs 4.3× less to evaluate than Sonnet 5 at max — and leads every benchmark by double digits.
Claude Opus 5.5 (Sep 2026) is Anthropic's flagship model; Claude Sonnet 5 (Jun 2026) is the predecessor to Sonnet 5.5. At $4/$20 vs $2/$10 per MTok, Opus appears more expensive — but Sonnet 5 at max effort generates so many more tokens that running the Intelligence Index costs 4.3× more ($6,998 vs $1,627 for Opus 5.5 at medium). This Claude Opus 5.5 vs Sonnet 5 comparison covers 9 benchmarks, per-task economics, speed, thinking mode differences, and when Sonnet 5 still makes sense.
Last updated 2026-10-01 · Vendor data sourced from Anthropic Opus 5.5 and Anthropic Sonnet 5
At a Glance: Claude Opus 5.5 or Claude Sonnet 5?
Choose Claude Opus 5.5 when…
You need peak quality, agentic coding, computer use, or complex knowledge work. Despite 2× higher per-token pricing, Opus at default effort costs far less to run than Sonnet 5 at max effort, thanks to much lower token usage. Fast mode available for latency-sensitive workloads.
Choose Claude Sonnet 5 when…
You need to disable thinking mode for trivial, non-reasoning tasks where adaptive thinking adds unnecessary latency and cost. This is the only advantage Sonnet 5 has over Opus 5.5. Consider Sonnet 5.5 instead for most use cases.
Claude Opus 5.5 vs Sonnet 5: Key Differences
Side-by-side comparison of specifications, pricing and capabilities — sourced from Anthropic and Artificial Analysis.
| Claude Opus 5.5 | Claude Sonnet 5 | |
|---|---|---|
| Intelligence Index (max) | 58 | 38 |
| Pricing (input / output) | $4 / $20 per MTok | $2 / $10 per MTok |
| Cost to run II (AA) | ~$1,627 (medium effort) | ~$6,998 (max effort, 4.3× more) |
| Cost per II task at max effort | $5.98 | $5.09 |
| Output tokens per task (AA) | ~26k (medium) | ~118k (max) |
| Output speed | ~72 t/s (medium) | ~79 t/s (max) |
| Fast mode | $8/$40, up to 2.5× speed | Not available |
| Knowledge cutoff | Jun 2026 | Jan 2026 (−5 months) |
| Thinking mode | Always on (cannot disable) | Adaptive (can be disabled) |
| Default effort | medium | high |
| Released | Sep 22, 2026 | Jun 30, 2026 |
Both share a 1M-token context window, 128K max output (300K on Batch API), text + image input, and the same platform availability (Claude API, Bedrock, Google Cloud, Microsoft Foundry, Claude Platform on AWS).
Claude Opus 5.5 vs Sonnet 5: Full Specifications
API identifiers, pricing tiers, context limits and reasoning behavior from Anthropic's official documentation.
| Spec | Claude Opus 5.5 | Claude Sonnet 5 |
|---|---|---|
| API model ID | claude-opus-5-5 | claude-sonnet-5 |
| Released | Sep 22, 2026 | Jun 30, 2026 |
| Tagline | For long-running agentic coding and knowledge work | Anthropic's balanced reasoning model (succeeded by Sonnet 5.5) |
| Latency | Moderate | Fast |
| Input price (per MTok) | $4 | $2 |
| Output price (per MTok) | $20 | $10 |
| Context window | 1M tokens | 1M tokens |
| Max output | 128K tokens (300K on Batch API) | 128K tokens (300K on Batch API) |
| Thinking | Adaptive, always on, cannot be disabled | Adaptive; can be disabled |
| Default effort | medium | high |
| Knowledge cutoff | Jun 2026 | Jan 2026 |
| Input modalities | Text + images | Text + images |
| Retirement | Not sooner than Sep 22, 2027 | Not sooner than Jun 30, 2027 |
Claude Opus 5.5 vs Sonnet 5: Pricing Paradox
Per-token pricing suggests Sonnet 5 is the budget option: $2/$10 vs $4/$20 per MTok. Cache reads are identical ($0.20). Sonnet 5 has cheaper cache writes ($2.50/$4 vs $5/$8) and batch pricing ($1/$5 vs $2/$10).
| Pricing Tier | Claude Opus 5.5 | Claude Sonnet 5 |
|---|---|---|
| Standard API (per MTok) | $4 / $20 | $2 / $10 |
| Batch API (50% off) | $2 / $10 | $1 / $5 |
| Cache write (5 min) | $5 | $2.50 |
| Cache write (1 hour) | $8 | $4 |
| Cache read | $0.20 (0.05x base) | $0.20 (0.1x base) |
But total cost depends on effort and token use. Artificial Analysis measured the cost to run its Intelligence Index at ~$1,627 for Opus 5.5 at medium effort (its default) vs ~$6,998 for Sonnet 5 at max effort — 4.3× less — because Opus used ~26k output tokens per task vs ~118k. Compare both at max effort and the gap closes: $5.98 per task for Opus vs $5.09 for Sonnet 5 (Opus ~17% higher), for 58 vs 38 on the index.
Opus 5.5 also offers a fast mode at $8/$40 per MTok with up to 2.5× speed boost. Sonnet 5 has no fast mode equivalent.
Benchmark Results: Claude Opus 5.5 Leads All 9 Evaluations
Benchmarks from Anthropic's Opus 5.5 announcement and Artificial Analysis.
| Benchmark | Claude Opus 5.5 | Claude Sonnet 5 | Delta | Note |
|---|---|---|---|---|
| Intelligence Index (max) | 58 | 38 | +20 | Artificial Analysis |
| Terminal-Bench 4.0 | 66.4% | 10.3% | +56.1 pp | Agentic coding |
| FrontierCode 1.1 Main | 54.4% | 42.4% | +12.0 pp | Max effort |
| CursorBench 4.0 | 57.8% | 34.1% | +23.7 pp | — |
| OSWorld 2.1 | 81.8% | 57.0% | +24.8 pp | Computer use |
| Chartography | 64.4% | 15.6% | +48.8 pp | Visual recognition |
| GDPval-AA v2.1 | 1846 Elo | 1449 Elo | +397 Elo | Knowledge work |
| AA-Briefcase v1.1 | 1822 Elo | 1359 Elo | +463 Elo | Business reasoning |
| Humanity's Last Exam | 67.7% | 54.9% | +12.8 pp | With tools |
Agentic coding shows the widest gaps. Terminal-Bench 4.0: 66.4% vs 10.3% (+56.1 pp) — Sonnet 5 is barely functional for autonomous coding while Opus 5.5 is a top-tier performer. CursorBench 4.0: 57.8% vs 34.1% (+23.7 pp).
Visual recognition is equally lopsided: Chartography 64.4% vs 15.6% (+48.8 pp). Sonnet 5 trails by nearly 49 points.
Business reasoning shows a full-tier gap: GDPval-AA +397 Elo and AA-Briefcase +463 Elo. Opus 5.5 operates at a fundamentally different level for knowledge work.
Output Speed: Claude Opus 5.5 vs Claude Sonnet 5 Compared
Artificial Analysis measures Opus 5.5 at medium effort at about 72 tokens per second and Sonnet 5 at max effort at about 79 tokens per second — Sonnet 5 is roughly 10% faster per token, yet Opus 5.5 scores 13 points higher on the Intelligence Index (51 vs 38).
In practice, Opus 5.5 can finish tasks sooner because it uses far fewer tokens: about 26k output tokens per task vs about 118k for Sonnet 5 on Artificial Analysis's evaluation suite.
For latency-critical workloads, Opus 5.5's fast mode ($8/$40) pushes speed up to 2.5× (~180 t/s). Sonnet 5 has no fast mode — about 79 t/s is its ceiling.
Thinking Mode: Claude Opus 5.5 vs Sonnet 5 Differences
Sonnet 5 can disable thinking mode. Sending thinking: disabled skips reasoning entirely — useful for trivial classification, extraction or formatting tasks where thinking adds latency and token cost without improving results.
Opus 5.5 has always-on adaptive thinking that cannot be turned off. Even at low effort, Opus always reasons before answering. This is the only capability where Sonnet 5 has an edge.
Note that Sonnet 5 defaults to high effort while Opus 5.5 defaults to medium. If you switch to Opus without adjusting the effort parameter, you may see a different thinking profile than expected.
Claude Opus 5.5 vs Sonnet 5: Which to Choose by Use Case
Match your workload to the right model.
| Scenario | Recommended | Why |
|---|---|---|
| Agentic coding | Opus 5.5 | Terminal-Bench +56.1 pp; CursorBench +23.7 pp |
| Computer use / automation | Opus 5.5 | OSWorld +24.8 pp (81.8% vs 57.0%) |
| Visual recognition | Opus 5.5 | Chartography +48.8 pp (64.4% vs 15.6%) |
| Business reasoning | Opus 5.5 | AA-Briefcase +463 Elo; GDPval-AA +397 Elo |
| Complex research tasks | Opus 5.5 | HLE +12.8 pp; 5-month fresher knowledge cutoff |
| Latency-sensitive API calls | Opus 5.5 | Fast mode 2.5× speed; no fast mode on Sonnet 5 |
| Budget-constrained high volume | Sonnet 5.5 | Same quality tier as Opus at $2/$10 |
| Non-reasoning trivial tasks | Sonnet 5 | Only Claude model that can disable thinking |
For most use cases, the real choice is between Opus 5.5 and Sonnet 5.5 — not Sonnet 5. Sonnet 5.5 nearly matches Opus benchmarks at half the per-token cost.
Claude Opus 5.5 vs Sonnet 5: The Bottom Line
Claude Opus 5.5 is the clear winner. It leads all 9 benchmarks — Intelligence Index 58 vs 38 (+20), Terminal-Bench 66.4% vs 10.3% (+56.1 pp), Chartography 64.4% vs 15.6% (+48.8 pp) — runs at a similar ~72 t/s output speed, and at its default medium effort costs 4.3× less to evaluate than Sonnet 5 at max ($1,627 vs $6,998 per II run) despite 2× higher per-token pricing. At max effort on both, per-task cost is close ($5.98 vs $5.09). Claude Sonnet 5's only advantage — disabling thinking mode — applies to a narrow set of trivial tasks. For anything requiring reasoning, coding, or knowledge work, Claude Opus 5.5 is both better and, at default effort, cheaper to run. If per-token rate is a concern, consider Sonnet 5.5, which nearly matches Opus quality at Sonnet pricing.
Claude Opus 5.5 vs Sonnet 5: FAQ
Is Claude Opus 5.5 better than Claude Sonnet 5?
Yes, significantly. Opus 5.5 leads all 9 tracked benchmarks by wide margins — Intelligence Index 58 vs 38, Terminal-Bench 66.4% vs 10.3%, OSWorld 81.8% vs 57.0%, and 400+ Elo on both GDPval-AA and AA-Briefcase. Opus 5.5 is a newer, higher-tier model released three months after Sonnet 5.
Is Claude Opus 5.5 more expensive than Claude Sonnet 5?
Per token, yes — Opus 5.5 costs $4/$20 per MTok vs Sonnet 5's $2/$10. But per task, the picture depends on effort. Artificial Analysis measured ~$1,627 to run its Intelligence Index on Opus 5.5 at medium effort (its default) vs ~$6,998 on Sonnet 5 at max effort — 4.3× less — because Opus used ~26k output tokens per task vs ~118k. At max effort on both, per-task cost is close: $5.98 for Opus vs $5.09 for Sonnet 5, with Opus scoring 58 vs 38.
How fast is Claude Opus 5.5 compared to Claude Sonnet 5?
Per token, Sonnet 5 is slightly faster: about 79 tokens per second vs about 72 for Opus 5.5 at medium effort, according to Artificial Analysis. But Opus 5.5 used about 26k output tokens per task vs about 118k for Sonnet 5, so it can finish tasks sooner in practice. Opus also has a fast mode ($8/$40) that boosts speed up to 2.5×; Sonnet 5 has no fast mode.
Should I use Claude Sonnet 5 instead of Claude Opus 5.5 to save money?
Usually no. Despite Sonnet 5's lower per-token price, running it at max effort cost 4.3× more than Opus 5.5 at its default medium effort on Artificial Analysis's Intelligence Index, because it used far more tokens. At max effort on both, per-task cost is similar ($5.98 vs $5.09). The exception is trivial tasks where you can disable thinking mode — Sonnet 5 supports this, Opus does not. For most workloads, Opus 5.5 delivers better results at a lower effective cost.
What is the Intelligence Index gap between Claude Opus 5.5 and Claude Sonnet 5?
At max effort, Opus 5.5 scores 58 vs Sonnet 5's 38 — a 20-point gap (53% higher). Even at medium effort, Opus scores 51, still 13 points above Sonnet 5 at max. The gap is one of the largest between any two active Claude models.
Can Claude Sonnet 5 disable thinking mode while Claude Opus 5.5 cannot?
Yes. Sonnet 5 supports sending thinking: disabled to skip reasoning entirely. Opus 5.5 has always-on adaptive thinking that cannot be turned off. This is the one capability Sonnet 5 has that Opus 5.5 does not.
How does Claude Opus 5.5 compare to Claude Sonnet 5 on coding tasks?
Opus 5.5 dominates coding benchmarks. Terminal-Bench 4.0: 66.4% vs 10.3% (+56.1 pp). CursorBench 4.0: 57.8% vs 34.1% (+23.7 pp). FrontierCode 1.1: 54.4% vs 42.4% (+12.0 pp). Sonnet 5 is barely functional for agentic coding, while Opus 5.5 is a top-tier performer.
What knowledge cutoff does Claude Opus 5.5 have vs Claude Sonnet 5?
Opus 5.5 has a June 2026 knowledge cutoff. Sonnet 5 has a January 2026 cutoff — 5 months older. For tasks requiring recent information, Opus 5.5 has a significant advantage.
Should I upgrade from Claude Sonnet 5 to Sonnet 5.5 or Opus 5.5?
If you want the best price-performance, upgrade to Sonnet 5.5 — it scores nearly as high as Opus 5.5 at half the per-token cost. If you need peak quality for complex agentic tasks and knowledge work, Opus 5.5 is the best Claude model available. Either is a massive improvement over Sonnet 5.
When were Claude Opus 5.5 and Claude Sonnet 5 released?
Claude Sonnet 5 launched on June 30, 2026. Claude Opus 5.5 followed on September 22, 2026 — about three months later. Opus 5.5 is part of a newer generation and is positioned as Anthropic's flagship model.
Related Comparisons
- Claude Opus 5.5 vs Claude Sonnet 5.5 — Opus vs the current Sonnet ($4/$20 vs $2/$10)
- Claude Sonnet 5 vs Claude Sonnet 5.5 — generational upgrade at the same $2/$10 pricing
- Claude Fable 5.1 vs Claude Opus 5.5 — Anthropic's premium tier vs flagship
- Claude Opus 5.5 vs GPT-6 Sol — cross-vendor at the $2-$4/$10-$20 tier
- Claude Opus 5.5 — full pricing, benchmarks and cost calculator
Sources & References
- Anthropic Claude Opus 5.5 Model Page
- Anthropic Claude Sonnet 5 Model Page
- Claude Opus 5.5 Announcement
- Anthropic Pricing
- Artificial Analysis: Opus 5.5 vs Sonnet 5
- Artificial Analysis: Claude Sonnet 5
- Emergent: Claude Opus 5.5 vs Claude Sonnet 5
- OrcaRouter: Opus 5.5 vs Sonnet 5 — Twenty Index Points
- The Decoder: Sonnet 5.5 Nearly Matches Opus 5.5