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GPT-6 Luna vs Claude Sonnet 5.5
Claude Sonnet 5.5 scores higher than GPT-6 Luna on all 4 public leaderboards that rate both. On the ArtificialWatch Index, which takes the median of each model's percentile across the boards that score it, GPT-6 Luna is at 31.4 and Claude Sonnet 5.5 at 90.3 (out of 100).
Scores as published by each board; table composed October 8, 2026.
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Leaderboard by leaderboard
| Board | GPT-6 Luna | Claude Sonnet 5.5 | Higher |
|---|---|---|---|
| LMArena Elo (community votes) | 1,580.9 | 1,774.3 | Claude Sonnet 5.5 |
| LiveBench global average (0-100) | 72 | 77.8 | Claude Sonnet 5.5 |
| Vals AI Vals Index accuracy % · weighted finance + coding tasks | 51.2 | 67 | Claude Sonnet 5.5 |
| Artificial Analysis intelligence index · measured runs only | 38.1 | 56 | 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, GPT-6 Luna is at 26.5 (#27 of 35) and Claude Sonnet 5.5 at 88.2 (#3). Claude Sonnet 5.5 scores higher on all 3 coding boards that rate both.
| Coding board | GPT-6 Luna | Claude Sonnet 5.5 |
|---|---|---|
| LMArena · Coding | 1,508.4 | 1,531.8 |
| LiveBench · Coding | 65.1 | 73.8 |
| Vals Vibe Code Bench | 81.6 | 92.4 |
GPT-6 Luna at a glance
- Developer
- OpenAI
- Status
- Live since September 22, 2026
- API price
- $0.10 input / $0.50 output per 1M tokens · OpenAI, gpt-6-luna
- Context window
- 1.05M tokens
Live — Sep 22, in the API and ChatGPT (Free and Go too) the same day · the cheap, high-volume tier · models.dev lists gpt-6-luna on OpenAI's own API (read Sep 24).
OpenAI opens the Decisions API: GPT-6 Luna returns probabilities, choices and scores for $0.10 per million input tokens
2026-10-06 · OpenAI has opened a public beta of the Decisions API, a new endpoint (POST /v1/decisions) where the model answers a question about your input with a number or a label instead of writing text. GPT-6 Luna is the only model it runs.
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.
GPT-6 Luna vs Claude Sonnet 5.5: quick answers
Which is better, GPT-6 Luna or Claude Sonnet 5.5?
It depends on what you measure. Claude Sonnet 5.5 scores higher than GPT-6 Luna on all 4 public leaderboards that rate both. Claude Sonnet 5.5's widest lead is on Artificial Analysis. On the ArtificialWatch Index, which takes the median of each model's percentile across the boards that score it, GPT-6 Luna is at 31.4 and Claude Sonnet 5.5 at 90.3 (out of 100).
Which is newer, GPT-6 Luna or Claude Sonnet 5.5?
Claude Sonnet 5.5. It went live on September 28, 2026, 6 days after GPT-6 Luna (September 22, 2026).
Which is cheaper, GPT-6 Luna or Claude Sonnet 5.5?
GPT-6 Luna is cheaper on both input and output. On each vendor's own API, GPT-6 Luna is $0.10 input / $0.50 output per million tokens and Claude Sonnet 5.5 is $2 input / $10 output per million tokens. GPT-6 Luna's rate rises for prompts over 272K tokens. Prices as published in the models.dev catalog, as of 2026-10-08.
Which has the bigger context window, GPT-6 Luna or Claude Sonnet 5.5?
GPT-6 Luna, at 1.05M tokens against Claude Sonnet 5.5's 1M, as each vendor lists it.
How do GPT-6 Luna and Claude Sonnet 5.5 compare for coding?
On the ArtificialWatch coding index, GPT-6 Luna is at 26.5 (#27 of 35) and Claude Sonnet 5.5 at 88.2 (#3). Claude Sonnet 5.5 scores higher on all 3 coding boards that rate both.
Who makes GPT-6 Luna and Claude Sonnet 5.5?
GPT-6 Luna is from OpenAI; Claude Sonnet 5.5 is 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