In short
How they differ.
Worked out from the figures below. Prices and specs are the makers' own, read Oct 20, 2026.
- GPT-6 Luna is cheaper per output token: $0.50 against $20 per million tokens, so Claude Opus 5.5 costs 40 times as much.
- GPT-6 Luna reads more at once: a context window of 1M tokens against 1M.
- On the 3 independent boards that rank both, Claude Opus 5.5 places higher on 3 and GPT-6 Luna on 0.
Side by side
The specs.
| Claude Opus 5.5 | GPT-6 Luna | |
|---|---|---|
| Made by | Anthropic · US | OpenAI · US |
| Released | Sep 22, 2026 | Sep 22, 2026 |
| Price per 1M tokens | $4 in / $20 out | $0.10 in / $0.50 out |
| Context window | 1M | 1M |
| Takes in | text, image | text, image |
| Download and run it yourself | No | No |
| Size | Not published | Not published |
| Maker says | “For long-running agentic coding and knowledge work” | “Our most efficient model for focused, high-volume tasks.” |
| Sources | Prices, Oct 20, 2026 · Description | Prices, Oct 20, 2026 · Description |
Independent tests
Where they place.
Position on each board we follow (1 is best). Epoch AI's and Vectara's scores are shown; the other boards are linked for their own figures.
| Board | Claude Opus 5.5 | GPT-6 Luna |
|---|---|---|
| Epoch Capabilities IndexEpoch AI, Oct 20, 2026 | #1166.82 | #27156.31 |
| LMArena textLMArena, Oct 15, 2026 | #3 | Not listed |
| LMArena creative writingLMArena, Oct 15, 2026 | #1 | Not listed |
| LMArena coding chatsLMArena, Oct 15, 2026 | #6 | Not listed |
| LMArena WebDevLMArena, Oct 19, 2026 | #1 | Not listed |
| LMArena mathLMArena, Oct 15, 2026 | #14 | Not listed |
| LMArena visionLMArena, Oct 19, 2026 | #10 | Not listed |
| LMArena Agent ArenaLMArena, Oct 19, 2026 | #1 | #19 |
| Humanity's Last ExamScale AI | #2 | Not listed |
| Remote Labor IndexScale AI | #1 | Not listed |
| Vals IndexVals AI, Oct 19, 2026 | #2 | #19 |
| Terminal-Bench 4.0Vals AI, Oct 19, 2026 | #1 | Not listed |
| Vibe Code BenchVals AI, Oct 18, 2026 | #5 | Not listed |
| ProofBenchVals AI, Oct 12, 2026 | #2 | Not listed |
| CUA-bench (games)Vals AI, Oct 13, 2026 | #2 | Not listed |
More comparisons