text model comparison
Claude Sonnet 5.5 vs GPT-6 Luna
Claude Sonnet 5.5 and GPT-6 Luna are both current text models, from Anthropic and OpenAI. GPT-6 Luna is 95% cheaper per 1M input tokens than Claude Sonnet 5.5, $0.10 vs $2. On Arena Text, Claude Sonnet 5.5 scores 1476 Elo and GPT-6 Luna 1443 Elo (Arena, measured October 8, 2026). GPT-6 Luna has the larger context window, 1,050,000 vs 1,000,000 tokens.
Data verified October 13, 2026 · Dataset 2026-10-13
Side by side
Prices in effect today, compared at the same tier wherever both list one. The better value in each row is highlighted.
| Fact | Claude Sonnet 5.5 | GPT-6 Luna |
|---|---|---|
| Price per 1M input tokens | $2 | $0.10 (better) |
| Price per 1M output tokens | $10 | $0.50 (better) |
| Arena Text | 1476 Elo (#20 of 49) (better) | 1443 Elo (#37 of 49) |
| GPQA Diamond | 95.6% (#2 of 40) (better) | 90.5% (#25 of 40) |
| FrontierMath Tiers 1-3 (v2) | 88.8% (#7 of 40) (better) | 78.9% (#14 of 40) |
| SimpleQA Verified | 46.5% (#22 of 36) (better) | 41.4% (#26 of 36) |
| Provider | Anthropic | OpenAI |
| Release date | September 28, 2026 | September 22, 2026 |
| Access | API only | API only |
| Context window | 1,000,000 tokens | 1,050,000 tokens |
| Max output | 128,000 tokens | 128,000 tokens |
| Input | text, image | text, image |
| Output | text | text |
What each costs
Example workloads at each provider's listed rates, then every other rate either one lists. The cheaper figure in each row is highlighted.
| Workload or rate | Claude Sonnet 5.5 | GPT-6 Luna |
|---|---|---|
| 10M input and 2M output tokens | $40 | $2 (better) |
| The same, with 9M of the input tokens cached | $22.90 | $1.19 (better) |
| The same, through the batch API | $20 | Not listed |
| Other listed rates | ||
| 1M input tokens, cached | $0.10 | $0.01 (better) |
| 1M input tokens, 5-minute cache write | $2.50 | Not listed |
| 1M input tokens, 1-hour cache write | $4 | Not listed |
| 1M input tokens, batch | $1 | Not listed |
| 1M output tokens, batch | $5 | Not listed |
| 1M input tokens, prompts over 272K tokens | Not listed | $0.20 |
| 1M output tokens, prompts over 272K tokens | Not listed | $0.75 |
When to choose each
Claude Sonnet 5.5
Where it leads
- Higher Arena Text score, 1476 Elo vs 1443 Elo
- Higher GPQA Diamond score, 95.6% vs 90.5%
- Higher FrontierMath Tiers 1-3 (v2) score, 88.8% vs 78.9%
- Higher SimpleQA Verified score, 46.5% vs 41.4%
- Batch pricing, $1 input and $5 output per 1M tokens
Best for
- Production workloads that need frontier-adjacent quality at a mid-tier rate
- Latency-sensitive agent steps inside a larger pipeline
Watch out for
- Same list price as Claude Sonnet 5, so the gain is capability and cache economics rather than a cheaper rate card
- Anthropic positions Opus 5.5 rather than this as the default, so reach for Sonnet 5.5 when latency matters more than peak capability
GPT-6 Luna
Where it leads
- Lower input and output prices, $0.10 and $0.50 vs $2 and $10 per 1M tokens
- Larger context window 1,050,000 vs 1,000,000 tokens
- Cheaper cached input, $0.01 vs $0.10 per 1M tokens
Best for
- High-volume summarisation, extraction and routing
- Long-context budget work, where the 272k threshold is more forgiving than Haiku 5.5's 100k
Watch out for
- Prompts over 272,000 tokens are rebilled at $0.20 input and $0.75 output for the whole request
- A twentieth of GPT-6 Sol's price reflects a capability gap, not a discount on the same model
Claude Sonnet 5.5 vs GPT-6 Luna FAQ
Which is cheaper, Claude Sonnet 5.5 or GPT-6 Luna?
GPT-6 Luna is 95% cheaper per 1M input tokens than Claude Sonnet 5.5, $0.10 vs $2. For 10M input and 2M output tokens, Claude Sonnet 5.5 costs $40 and GPT-6 Luna $2 at standard rates.
Which is cheaper with prompt caching, Claude Sonnet 5.5 or GPT-6 Luna?
Claude Sonnet 5.5 charges $0.10 per 1M cached input tokens, 95% below its standard input rate, and GPT-6 Luna $0.01, 90% below. With 9M of 10M input tokens cached and 2M output tokens, Claude Sonnet 5.5 costs $22.90 and GPT-6 Luna $1.19.
Which scores higher on independent benchmarks, Claude Sonnet 5.5 or GPT-6 Luna?
Claude Sonnet 5.5 leads on Arena Text, 1476 Elo to 1443 Elo; Claude Sonnet 5.5 leads on GPQA Diamond, 95.6% to 90.5%; Claude Sonnet 5.5 leads on FrontierMath Tiers 1-3 (v2), 88.8% to 78.9%. Scores are independent evaluations, not either vendor's launch figures.
Which has the larger context window, Claude Sonnet 5.5 or GPT-6 Luna?
GPT-6 Luna has the larger context window, 1,050,000 vs 1,000,000 tokens. Both return up to 128,000 tokens per response.
Articles on Claude Sonnet 5.5 and GPT-6 Luna
- Claude Sonnet 5.5 vs GPT-6 Luna: Cost, Speed and AccuracySeptember 29, 2026 · compares both
- Claude Sonnet 5.5: Benchmarks, Price and When to Use OpusSeptember 29, 2026
- GPT-6 Sol vs Claude Opus 5.5, Plus Luna: Best Value per TaskSeptember 24, 2026
- GPT-6 Sol and Luna: Half the Price, and Where Each One FitsSeptember 23, 2026
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- Claude Sonnet 5.5 vs GPT-5.6 Terra
- GPT-6 Astra vs GPT-6 Luna
- Claude Sonnet 5.5 vs GPT-6 Sol
- GPT-6 Luna vs GPT-6 Sol
- Claude Sonnet 5.5 vs Grok 4.5
- GPT-6 Luna vs Grok 4.3
Production evaluation
Choosing between Claude Sonnet 5.5 and GPT-6 Luna?
Public benchmarks narrow the shortlist. We run both on your own tasks, data and cost limits, then build the routing and review controls to run the winner in production.
- A head-to-head evaluation on your real workload
- Routing between models by cost and difficulty