GPT-5.6 Luna vs GPT-6 Astra
GPT-5.6 Luna was superseded by GPT-6 Luna.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.
GPT-6 Astra leads overall, C to D. GPT-5.6 Luna is the cheaper side per task (at most $0.012). By suite, real-world issues is even at D and GPT-6 Astra takes 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-6 Astra vs GPT-5.6 Luna
GPT-6 Astra leads overall, C to D. By suite: real-world issues is even at D (45% vs 43% capability); GPT-6 Astra takes spec planning, C+ to C- (74% vs 57% capability); GPT-6 Astra takes vibe coding, C+ to F (74% vs 25% 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. GPT-6 Astra used 22% of ChatGPT Plus's weekly limit per pass, $0.053 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~4.4% of ChatGPT Pro 5x's weekly limit (est, about $0.053 per task). Per task, GPT-5.6 Luna costs at most $0.012 against GPT-6 Astra's $0.053, so GPT-5.6 Luna is the cheaper side. GPT-6 Astra is faster on real-world issues: a median task takes 2m 13s 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 $0.053).
Changed since W38: GPT-5.6 Luna: spec planning D+ to C-, vibe coding C- to F; GPT-6 Astra has one graded week under this version (W40).
| Dimension | GPT-5.6 Luna | GPT-6 Astra | Advantage |
|---|---|---|---|
| Capability | 45% | 43% | +2% (GPT-5.6 Luna leads) |
| Median task time | 3m 7s | 2m 13s | 54s faster (GPT-6 Astra leads) |
| Approx. task cost | <$0.015 / task | $0.052 / task | $0.037 / task lower (GPT-5.6 Luna leads) |
GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per run. GPT-6 Astra: 17.0% of ChatGPT Plus (112.0% / 5h, 17.0% / 1w) 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 | GPT-5.6 Luna | GPT-6 Astra | Advantage |
|---|---|---|---|
| Capability | 57% | 74% | +18% (GPT-6 Astra leads) |
| Median task time | 3m 25s | 3m 5s | 20s faster (GPT-6 Astra leads) |
| Approx. task cost | <$0.057 / task | $0.057 / task | Even |
GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per run. GPT-6 Astra: 5.0% of ChatGPT Plus (27.0% / 5h, 5.0% / 1w) 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 | GPT-5.6 Luna | GPT-6 Astra | Advantage |
|---|---|---|---|
| Capability | 25% | 74% | +49% (GPT-6 Astra leads) |
| Median task time | 3m 40s | 2m 40s | 1m 0s faster (GPT-6 Astra leads) |
| Approx. task cost | <$0.230 / task | $0.046 / task | $0.184 / task lower (GPT-6 Astra leads) |
GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per good solve. GPT-6 Astra: 1.0% of ChatGPT Plus (7.2% / 5h, 1.0% / 1w) 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, GPT-5.6 Luna or GPT-6 Astra?
GPT-6 Astra clears higher: tier 2 of 5 versus tier 1 for GPT-5.6 Luna on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-21.
Which is cheaper per task, GPT-5.6 Luna or GPT-6 Astra?
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. GPT-6 Astra used 22% of ChatGPT Plus's weekly limit per pass, $0.053 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~4.4% of ChatGPT Pro 5x's weekly limit (est, about $0.053 per task). Per task, GPT-5.6 Luna costs at most $0.012 against GPT-6 Astra's $0.053, so GPT-5.6 Luna is the cheaper side.
What do GPT-5.6 Luna and GPT-6 Astra cost a month?
GPT-5.6 Luna runs on ChatGPT Pro 5x at $100/month (public price as of 2026-09-05). GPT-6 Astra runs on ChatGPT Plus at $20/month (public price as of 2026-07-20).