GPT-5.6 Luna vs Composer 2.5
GPT-5.6 Luna was superseded by GPT-6 Luna.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, Composer 2.5 takes real-world issues (C- 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: Composer 2.5 vs GPT-5.6 Luna
Both grade D overall. By suite: Composer 2.5 takes real-world issues, C- to D (57% vs 45% capability); GPT-5.6 Luna takes spec planning, C- to D (57% vs 48% capability); vibe coding is even at F (25% vs 23% capability). 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. Composer 2.5 used 2.0% of Cursor Pro's monthly limit per pass, $0.021 per task at the listed price. Per task, GPT-5.6 Luna costs at most $0.012 against Composer 2.5's $0.021, so GPT-5.6 Luna is the cheaper side. Composer 2.5 is faster on real-world issues: a median task takes 1m 34s against 3m 7s. Both finished every task on it.
Changed since the previous graded week: GPT-5.6 Luna: spec planning D+ to C-, vibe coding C- to F; Composer 2.5: real-world issues D+ to C-.
| Dimension | GPT-5.6 Luna | Composer 2.5 | Advantage |
|---|---|---|---|
| Capability | 45% | 57% | +12% (Composer 2.5 leads) |
| Median task time | 3m 7s | 1m 34s | 1m 33s faster (Composer 2.5 leads) |
| Approx. task cost | <$0.015 / task | $0.021 / task | $0.006 / task lower (GPT-5.6 Luna leads) |
GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per run. Composer 2.5: 1.6% of Cursor Pro (1.6% / 1m) per run. Each figure is a share of that agent's own plan, so there is no delta to draw.
| Dimension | GPT-5.6 Luna | Composer 2.5 | Advantage |
|---|---|---|---|
| Capability | 57% | 48% | +9% (GPT-5.6 Luna leads) |
| Median task time | 3m 25s | 1m 8s | 2m 18s faster (Composer 2.5 leads) |
| Approx. task cost | <$0.057 / task | $0.022 / task | $0.035 / task lower (Composer 2.5 leads) |
GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per run. Composer 2.5: 0.4% of Cursor Pro (0.4% / 1m) per run. Each figure is a share of that agent's own plan, so there is no delta to draw.
| Dimension | GPT-5.6 Luna | Composer 2.5 | Advantage |
|---|---|---|---|
| Capability | 25% | 23% | +3% (GPT-5.6 Luna leads) |
| Median task time | 3m 40s | 1m 37s | 2m 3s faster (Composer 2.5 leads) |
| Approx. task cost | <$0.230 / task | $0.022 / task | $0.208 / task lower (Composer 2.5 leads) |
GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per good solve. Composer 2.5: 0.1% of Cursor Pro (0.1% / 1m) 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, GPT-5.6 Luna or Composer 2.5?
Both clear tier 1 of 5, but Composer 2.5 scores higher on capability: 57% versus 45% on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-21.
Which is cheaper per task, GPT-5.6 Luna or Composer 2.5?
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. Composer 2.5 used 2.0% of Cursor Pro's monthly limit per pass, $0.021 per task at the listed price. Per task, GPT-5.6 Luna costs at most $0.012 against Composer 2.5's $0.021, so GPT-5.6 Luna is the cheaper side.
What do GPT-5.6 Luna and Composer 2.5 cost a month?
GPT-5.6 Luna runs on ChatGPT Pro 5x at $100/month (public price as of 2026-09-05). Composer 2.5 runs on Cursor Pro at $20/month (public price as of 2026-07-20).