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Claude Sonnet 5.5 vs Claude Opus 5.5
Of the 6 public leaderboards that rate both, Claude Sonnet 5.5 scores higher on 1 and Claude Opus 5.5 on 5. On the ArtificialWatch Index, which takes the median of each model's percentile across the boards that score it, Claude Sonnet 5.5 is at 90.3 and Claude Opus 5.5 at 100 (out of 100).
Scores as published by each board; table composed October 8, 2026.
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Leaderboard by leaderboard
| Board | Claude Sonnet 5.5 | Claude Opus 5.5 | Higher |
|---|---|---|---|
| LMArena Elo (community votes) | 1,774.3 | 1,813 | Claude Opus 5.5 |
| LiveBench global average (0-100) | 77.8 | 83.2 | Claude Opus 5.5 |
| SimpleBench AVG@5 % (private set) | 75.9 | 88.4 | Claude Opus 5.5 |
| LLM Stats LLM Stats Score · composite (0-100), their rendered top 15 | 58.3 | 60.4 | Claude Opus 5.5 |
| Vals AI Vals Index accuracy % · weighted finance + coding tasks | 67 | 67 | Claude Sonnet 5.5 |
| Artificial Analysis intelligence index · measured runs only | 56 | 57.6 | Claude Opus 5.5 |
Raw scores are each board's own scale, so compare within a row, not across rows. Full table: the bench index.
For coding
On the ArtificialWatch coding index, Claude Sonnet 5.5 is at 88.2 (#3 of 35) and Claude Opus 5.5 at 96.9 (#1). Claude Sonnet 5.5 scores higher on 1 of the 3 coding boards that rate both and Claude Opus 5.5 on 2.
| Coding board | Claude Sonnet 5.5 | Claude Opus 5.5 |
|---|---|---|
| LMArena · Coding | 1,531.8 | 1,549.5 |
| LiveBench · Coding | 73.8 | 80.5 |
| Vals Vibe Code Bench | 92.4 | 90.3 |
Claude Sonnet 5.5 at a glance
- Developer
- Anthropic
- Status
- Live since September 28, 2026
- API price
- $2 input / $10 output per 1M tokens · Anthropic, claude-sonnet-5-5
- Context window
- 1M tokens
Live — Sep 28 · $2/$10 per MTok, the same as Sonnet 5 · cache reads $0.20 at launch, halved to $0.10 on Oct 7, writes $2.50 · in the API, the Claude apps, AWS, Google Cloud and Azure the same day · 1M ctx / 128K out · knowledge cutoff Jun 2026 · Artificial Analysis Intelligence Index 56 at max effort, #3 of 216 reasoning models (read Sep 28) · Anthropic's own table: Terminal-Bench 4.0 70.6% (Opus 5.5 66.4%), OSWorld 2.1 80.1% (Opus 5.5 81.8%) · our sweep caught claude-sonnet-5-5 at 17:54 UTC and fired at 17:55.
Claude Sonnet 5.5 ships at Sonnet 5's price, and the first independent number puts it #3 among reasoning models
2026-09-28 · Claude Sonnet 5.5 is live. Our sweep read the id claude-sonnet-5-5 at 17:54:45 UTC on September 28 and the alert went out at 17:55:45, 60 seconds later, to 314 inboxes and one phone. OpenRouter listed it nine minutes after that.
Claude Sonnet 5.5: named by Anthropic, reportedly in partner testing, priced 89% by Sep 30
2026-09-27 · Anthropic has named Claude Sonnet 5.5 but has not dated it. Everything past the name is reported, not confirmed - and the one number that moves every day says it is close.
Claude Opus 5.5 at a glance
- Developer
- Anthropic
- Status
- Live since September 22, 2026
- API price
- $4 input / $20 output per 1M tokens · Anthropic, claude-opus-5-5
- Context window
- 1M tokens
Live — Sep 22 · $4/$20 per MTok, down from Opus 5 at $5/$25 · 1M ctx / 128K out · adaptive thinking always on, default effort medium · cache reads 5% of base input · Anthropic now says start here for most workloads, and Opus 5 is legacy.
Claude Opus 5.5 ships at $4/$20 - and that is LESS than the Opus 5 it replaces
2026-09-22 · Claude Opus 5.5 is live. Our sweep read the id claude-opus-5-5 at 16:24:44 UTC on September 22 and the alert went out at 16:25:45 - 61 seconds later, to 307 inboxes and one phone. The hunt that caught it was armed the previous day, before the model had a confirmed name, on the version range rather than on the rumour.
Markets put the next Claude Opus at 83% by Thursday — the name going around is 5.5
2026-09-21 · Polymarket's "Next Claude Opus released by...?" book, read directly at 06:49 UTC, September 21: 83% by September 24, 91% by September 27, 95% by September 30. Polymarket's own post about nine hours earlier had Thursday at 72%, so the number has been climbing through the day.
Claude Sonnet 5.5 vs Claude Opus 5.5: quick answers
Which is better, Claude Sonnet 5.5 or Claude Opus 5.5?
It depends on what you measure. Of the 6 public leaderboards that rate both, Claude Sonnet 5.5 scores higher on 1 and Claude Opus 5.5 on 5. Claude Sonnet 5.5's widest lead is on Vals AI; Claude Opus 5.5's widest lead is on SimpleBench. On the ArtificialWatch Index, which takes the median of each model's percentile across the boards that score it, Claude Sonnet 5.5 is at 90.3 and Claude Opus 5.5 at 100 (out of 100).
Which is newer, Claude Sonnet 5.5 or Claude Opus 5.5?
Claude Sonnet 5.5. It went live on September 28, 2026, 6 days after Claude Opus 5.5 (September 22, 2026).
Which is cheaper, Claude Sonnet 5.5 or Claude Opus 5.5?
Claude Sonnet 5.5 is cheaper on both input and output. On each vendor's own API, Claude Sonnet 5.5 is $2 input / $10 output per million tokens and Claude Opus 5.5 is $4 input / $20 output per million tokens. Prices as published in the models.dev catalog, as of 2026-10-08.
Which has the bigger context window, Claude Sonnet 5.5 or Claude Opus 5.5?
Neither. Both take 1M tokens.
How do Claude Sonnet 5.5 and Claude Opus 5.5 compare for coding?
On the ArtificialWatch coding index, Claude Sonnet 5.5 is at 88.2 (#3 of 35) and Claude Opus 5.5 at 96.9 (#1). Claude Sonnet 5.5 scores higher on 1 of the 3 coding boards that rate both and Claude Opus 5.5 on 2.
Who makes Claude Sonnet 5.5 and Claude Opus 5.5?
Both are from Anthropic.
Where do these numbers come from?
Each score is the leaderboard's own published figure, read by ArtificialWatch (table composed October 8, 2026). Boards measure different things, so raw scores are only comparable within a row.
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