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Claude Sonnet 5.5 vs Claude Sonnet 5
Claude Sonnet 5.5 scores higher than Claude Sonnet 5 on all 5 public leaderboards that rate both. 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 Sonnet 5 at 32.4 (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 Sonnet 5 | Higher |
|---|---|---|---|
| LMArena Elo (community votes) | 1,774.3 | 1,540.8 | Claude Sonnet 5.5 |
| LiveBench global average (0-100) | 77.8 | 76 | Claude Sonnet 5.5 |
| SimpleBench AVG@5 % (private set) | 75.9 | 60.6 | Claude Sonnet 5.5 |
| Vals AI Vals Index accuracy % · weighted finance + coding tasks | 67 | 51.8 | Claude Sonnet 5.5 |
| Artificial Analysis intelligence index · measured runs only | 56 | 38.2 | Claude Sonnet 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 Sonnet 5 at 52.9 (#15). Claude Sonnet 5.5 scores higher on all 3 coding boards that rate both.
| Coding board | Claude Sonnet 5.5 | Claude Sonnet 5 |
|---|---|---|
| LMArena · Coding | 1,531.8 | 1,519.1 |
| LiveBench · Coding | 73.8 | 70 |
| Vals Vibe Code Bench | 92.4 | 81.3 |
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 Sonnet 5 at a glance
- Developer
- Anthropic
- Status
- Live since June 30, 2026
- API price
- $2 input / $10 output per 1M tokens · Anthropic, claude-sonnet-5
- Context window
- 1M tokens
Shipped Jun 30.
Claude Sonnet 5.5 vs Claude Sonnet 5: quick answers
Which is better, Claude Sonnet 5.5 or Claude Sonnet 5?
It depends on what you measure. Claude Sonnet 5.5 scores higher than Claude Sonnet 5 on all 5 public leaderboards that rate both. Claude Sonnet 5.5's widest lead is on LMArena. 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 Sonnet 5 at 32.4 (out of 100).
Which is newer, Claude Sonnet 5.5 or Claude Sonnet 5?
Claude Sonnet 5.5. It went live on September 28, 2026, 90 days after Claude Sonnet 5 (June 30, 2026).
Which is cheaper, Claude Sonnet 5.5 or Claude Sonnet 5?
They cost the same per token. On each vendor's own API, Claude Sonnet 5.5 is $2 input / $10 output per million tokens and Claude Sonnet 5 is $2 input / $10 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 Sonnet 5?
Neither. Both take 1M tokens.
How do Claude Sonnet 5.5 and Claude Sonnet 5 compare for coding?
On the ArtificialWatch coding index, Claude Sonnet 5.5 is at 88.2 (#3 of 35) and Claude Sonnet 5 at 52.9 (#15). Claude Sonnet 5.5 scores higher on all 3 coding boards that rate both.
Who makes Claude Sonnet 5.5 and Claude Sonnet 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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Also: the bench index · API pricing · the wire