Claude Opus 5.5 vs GPT-5.6 Luna
GPT-5.6 Luna was superseded by GPT-6 Luna. The grades below are the last ones measured, so read them as history rather than as this week's board. See the current roster.
Claude Opus 5.5 leads overall, B- to D. GPT-5.6 Luna is the cheaper side per task (at most $0.012). By suite, Claude Opus 5.5 takes real-world issues (C+ to D) and spec planning (C+ to C-). Take GPT-5.6 Luna anyway when you want the side that is cheaper per task.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-5.6 Luna vs Claude Opus 5.5
Claude Opus 5.5 leads overall, B- to D. By suite: Claude Opus 5.5 takes real-world issues, C+ to D (73% vs 45% capability); Claude Opus 5.5 takes spec planning, C+ to C- (73% vs 57% capability); Claude Opus 5.5 takes vibe coding, B+ to F (90% vs 25% capability). Claude Opus 5.5 used 2% of Claude Max 5x's weekly limit per pass, $0.024 per task at the listed price. GPT-5.6 Luna used <1% of ChatGPT Pro 5x's weekly limit per pass, at most $0.012 per task at the listed price. Per task, GPT-5.6 Luna costs at most $0.012 against Claude Opus 5.5's $0.024, so GPT-5.6 Luna is the cheaper side. Claude Opus 5.5 is faster on real-world issues: a median task takes 1m 17s against 3m 7s. Both finished every task on it. Reasons to pick GPT-5.6 Luna anyway: it is cheaper per task (at most $0.012 vs $0.024).
Changed since the previous graded week: Claude Opus 5.5: real-world issues C- to C+, vibe coding B to B+; GPT-5.6 Luna: spec planning D+ to C-, vibe coding C- to F.
| Dimension | Claude Opus 5.5 | GPT-5.6 Luna | Advantage |
|---|---|---|---|
| Capability | 73% | 45% | +28% (Claude Opus 5.5 leads) |
| Median task time | 1m 17s | 3m 7s | 1m 50s faster (Claude Opus 5.5 leads) |
| Approx. task cost | $0.015 / task | <$0.015 / task | Even |
Claude Opus 5.5: 11.0% of Claude Max 5x (11.0% / 5h, 1.0% / 1w) per run. Its weekly limit holds about 13.8 of the week's 33.6 5h windows. GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per run. Each figure is a share of that agent's own plan, so there is no delta to draw.
| Dimension | Claude Opus 5.5 | GPT-5.6 Luna | Advantage |
|---|---|---|---|
| Capability | 73% | 57% | +16% (Claude Opus 5.5 leads) |
| Median task time | 4m 17s | 3m 25s | 51s faster (GPT-5.6 Luna leads) |
| Approx. task cost | $0.057 / task | <$0.057 / task | Even |
Claude Opus 5.5: 6.0% of Claude Max 5x (6.0% / 5h, 1.0% / 1w) per run. Its weekly limit holds about 13.8 of the week's 33.6 5h windows. GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per run. Each figure is a share of that agent's own plan, so there is no delta to draw.
| Dimension | Claude Opus 5.5 | GPT-5.6 Luna | Advantage |
|---|---|---|---|
| Capability | 90% | 25% | +65% (Claude Opus 5.5 leads) |
| Median task time | 2m 44s | 3m 40s | 56s faster (Claude Opus 5.5 leads) |
| Approx. task cost | $0.007 / task | <$0.230 / task | $0.223 / task lower (Claude Opus 5.5 leads) |
Claude Opus 5.5: 1.0% of Claude Max 5x (1.0% / 5h) per good solve. Its weekly limit holds about 13.8 of the week's 33.6 5h windows. GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per good solve. 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 Opus 5.5 or GPT-5.6 Luna?
Claude Opus 5.5 clears higher: tier 4 of 5 versus tier 1 for GPT-5.6 Luna on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-28.
Which is cheaper per task, Claude Opus 5.5 or GPT-5.6 Luna?
Claude Opus 5.5 used 2% of Claude Max 5x's weekly limit per pass, $0.024 per task at the listed price. GPT-5.6 Luna used <1% of ChatGPT Pro 5x's weekly limit per pass, at most $0.012 per task at the listed price. Per task, GPT-5.6 Luna costs at most $0.012 against Claude Opus 5.5's $0.024, so GPT-5.6 Luna is the cheaper side.
What do Claude Opus 5.5 and GPT-5.6 Luna cost a month?
Claude Opus 5.5 runs on Claude Max 5x at $100/month (public price as of 2026-07-27). GPT-5.6 Luna runs on ChatGPT Pro 5x at $100/month (public price as of 2026-09-05).