Claude Sonnet 5 vs GPT-5.6 Luna
Claude Sonnet 5 is no longer on the leaderboard. GPT-5.6 Luna was superseded by GPT-6 Luna.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.
Both grade D overall. GPT-5.6 Luna is the cheaper side per task (at most $0.012). By suite, Claude Sonnet 5 takes real-world issues (D+ to D) and GPT-5.6 Luna takes spec planning (C- to D). Both agents run the same private suite cut headless through their own tools, each on its own subscription.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 Sonnet 5
Both grade D overall. By suite: Claude Sonnet 5 takes real-world issues, D+ to D (53% vs 45% capability); GPT-5.6 Luna takes spec planning, C- to D (57% vs 44% capability); vibe coding is even at F (31% vs 25% capability). Claude Sonnet 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 Sonnet 5's $0.024, so GPT-5.6 Luna is the cheaper side. GPT-5.6 Luna is faster on real-world issues: a median task takes 3m 7s against 3m 35s. Both finished every task on it.
Changed since the previous graded week: Claude Sonnet 5: vibe coding D+ to F; GPT-5.6 Luna: spec planning D+ to C-, vibe coding C- to F.
| Dimension | Claude Sonnet 5 | GPT-5.6 Luna | Advantage |
|---|---|---|---|
| Capability | 53% | 45% | +8% (Claude Sonnet 5 leads) |
| Median task time | 3m 35s | 3m 7s | 28s faster (GPT-5.6 Luna leads) |
| Approx. task cost | $0.015 / task | <$0.015 / task | Even |
Claude Sonnet 5: 12.0% of Claude Max 5x (12.0% / 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 Sonnet 5 | GPT-5.6 Luna | Advantage |
|---|---|---|---|
| Capability | 44% | 57% | +13% (GPT-5.6 Luna leads) |
| Median task time | 5m 12s | 3m 25s | 1m 46s faster (GPT-5.6 Luna leads) |
| Approx. task cost | $0.057 / task | <$0.057 / task | Even |
Claude Sonnet 5: 5.0% of Claude Max 5x (5.0% / 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 Sonnet 5 | GPT-5.6 Luna | Advantage |
|---|---|---|---|
| Capability | 31% | 25% | +6% (Claude Sonnet 5 leads) |
| Median task time | 4m 31s | 3m 40s | 51s faster (GPT-5.6 Luna leads) |
| Approx. task cost | $0.007 / task | <$0.230 / task | $0.223 / task lower (Claude Sonnet 5 leads) |
Claude Sonnet 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 Sonnet 5 or GPT-5.6 Luna?
Claude Sonnet 5 clears higher: tier 3 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 Sonnet 5 or GPT-5.6 Luna?
Claude Sonnet 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 Sonnet 5's $0.024, so GPT-5.6 Luna is the cheaper side.
What do Claude Sonnet 5 and GPT-5.6 Luna cost a month?
Claude Sonnet 5 runs on Claude Max 5x at $100/month (public price as of 2026-07-20). GPT-5.6 Luna runs on ChatGPT Pro 5x at $100/month (public price as of 2026-09-05).