Claude Sonnet 5.5 vs GPT-6 Luna
Claude Sonnet 5.5 leads overall, C- to D. By suite, real-world issues is even at C- and Claude Sonnet 5.5 takes spec planning (C+ to D+). The data gives no reason to pick GPT-6 Luna over Claude Sonnet 5.5 this week.Measured
Each agent graded on the same private suites, running headless through its own tools. Advantages are oriented so a win is a win, whichever way the metric runs.
Verdict: GPT-6 Luna vs Claude Sonnet 5.5
Claude Sonnet 5.5 leads overall, C- to D. By suite: real-world issues is even at C- (60% vs 57% capability); Claude Sonnet 5.5 takes spec planning, C+ to D+ (74% vs 55% capability); Claude Sonnet 5.5 takes vibe coding, D+ to F (48% vs 31% capability). Claude Sonnet 5.5 used <1% of Claude Max 5x's weekly limit per pass, $0.003 per task at the listed price. GPT-6 Luna used <1% of ChatGPT Plus's weekly limit per pass; at the ~$100 tier the board defaults to that is an estimated ~<0.2% of ChatGPT Pro 5x's weekly limit (est). Claude Sonnet 5.5 is faster on real-world issues: a median task takes 37s against 1m 4s. Both finished every task on it. The data gives no reason to pick GPT-6 Luna over Claude Sonnet 5.5 this week.
Changed since W39: GPT-6 Luna: real-world issues D+ to C-, spec planning C- to D+.
| Dimension | Claude Sonnet 5.5 | GPT-6 Luna | Advantage |
|---|---|---|---|
| Capability | 60% | 57% | +3% (Claude Sonnet 5.5 leads) |
| Median task time | 37s | 1m 4s | 27s faster (Claude Sonnet 5.5 leads) |
| Approx. task cost | $0.002 / task | not measured | - |
Claude Sonnet 5.5: 4.0% of Claude Max 5x (4.0% / 5h) per run. Its weekly limit holds about 13.8 of the week's 33.6 5h windows. GPT-6 Luna: under 1% of ChatGPT Plus (2.0% / 5h) per run. Its weekly limit holds about 6 of the week's 33.6 5h windows. Each figure is a share of that agent's own plan, so there is no delta to draw.
| Dimension | Claude Sonnet 5.5 | GPT-6 Luna | Advantage |
|---|---|---|---|
| Capability | 74% | 55% | +19% (Claude Sonnet 5.5 leads) |
| Median task time | 3m 25s | 1m 20s | 2m 5s faster (GPT-6 Luna leads) |
| Approx. task cost | $0.007 / task | <$0.011 / task | $0.005 / task lower (Claude Sonnet 5.5 leads) |
Claude Sonnet 5.5: 4.0% of Claude Max 5x (4.0% / 5h) per run. Its weekly limit holds about 13.8 of the week's 33.6 5h windows. GPT-6 Luna: under 1% of ChatGPT Plus per run. Its weekly limit holds about 6 of the week's 33.6 5h windows. Each figure is a share of that agent's own plan, so there is no delta to draw.
| Dimension | Claude Sonnet 5.5 | GPT-6 Luna | Advantage |
|---|---|---|---|
| Capability | 48% | 31% | +17% (Claude Sonnet 5.5 leads) |
| Median task time | 56s | 1m 24s | 27s faster (Claude Sonnet 5.5 leads) |
| Approx. task cost | $0.001 / task | <$0.046 / task | $0.045 / task lower (Claude Sonnet 5.5 leads) |
Claude Sonnet 5.5: 0.2% of Claude Max 5x (0.2% / 5h) per good solve. Its weekly limit holds about 13.8 of the week's 33.6 5h windows. GPT-6 Luna: under 1% of ChatGPT Plus per good solve. Its weekly limit holds about 6 of the week's 33.6 5h windows. Each figure is a share of that agent's own plan, so there is no delta to draw.
Grades and deltas are comparable only within a suite version. See methodology.
Frequently asked questions
Which is better for coding, Claude Sonnet 5.5 or GPT-6 Luna?
Claude Sonnet 5.5 clears higher: tier 4 of 5 versus tier 2 for GPT-6 Luna on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-28.
Which is cheaper per task, Claude Sonnet 5.5 or GPT-6 Luna?
Claude Sonnet 5.5 used <1% of Claude Max 5x's weekly limit per pass, $0.003 per task at the listed price. GPT-6 Luna used <1% of ChatGPT Plus's weekly limit per pass; at the ~$100 tier the board defaults to that is an estimated ~<0.2% of ChatGPT Pro 5x's weekly limit (est).
What do Claude Sonnet 5.5 and GPT-6 Luna cost a month?
Claude Sonnet 5.5 runs on Claude Max 5x at $100/month (public price as of 2026-07-20). GPT-6 Luna runs on ChatGPT Plus at $20/month (public price as of 2026-07-20).