GPT-6 Astra vs Kimi K3 256K
GPT-6 Astra leads overall, C to D+. GPT-6 Astra is about 2.7x cheaper per task. By suite, Kimi K3 256K takes real-world issues (C- to D) and GPT-6 Astra takes spec planning (C+ to C-). Take Kimi K3 256K anyway when you want the side that is ahead on real-world issues.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: Kimi K3 256K vs GPT-6 Astra
GPT-6 Astra leads overall, C to D+. By suite: Kimi K3 256K takes real-world issues, C- to D (60% vs 43% capability); GPT-6 Astra takes spec planning, C+ to C- (74% vs 56% capability); GPT-6 Astra takes vibe coding, C+ to F (74% vs 34% capability). 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). Kimi K3 256K used 31% of Kimi Allegretto's weekly limit per pass, $0.146 per task at the listed price. Per task, GPT-6 Astra is about 2.7x cheaper ($0.053 vs $0.146). GPT-6 Astra is faster on real-world issues: a median task takes 2m 13s against 3m 31s. Both finished every task on it. Reasons to pick Kimi K3 256K anyway: it leads on real-world issues (C- to D).
Changed since W39: GPT-6 Astra has one graded week under this version (W40); Kimi K3 256K: real-world issues usage 23% to 21% of the weekly limit, spec planning D+ to C-, spec planning usage 11% to 10% of the weekly limit, vibe coding usage 3% to 2.6% of the weekly limit.
| Dimension | GPT-6 Astra | Kimi K3 256K | Advantage |
|---|---|---|---|
| Capability | 43% | 60% | +17% (Kimi K3 256K leads) |
| Median task time | 2m 13s | 3m 31s | 1m 18s faster (GPT-6 Astra leads) |
| Approx. task cost | $0.052 / task | $0.126 / task | $0.073 / task lower (GPT-6 Astra leads) |
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. Kimi K3 256K: 104.0% of Kimi Allegretto (104.0% / 5h, 21.0% / 1w) per run. Its weekly limit holds about 5 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-6 Astra | Kimi K3 256K | Advantage |
|---|---|---|---|
| Capability | 74% | 56% | +18% (GPT-6 Astra leads) |
| Median task time | 3m 5s | 5m 26s | 2m 21s faster (GPT-6 Astra leads) |
| Approx. task cost | $0.057 / task | $0.224 / task | $0.167 / task lower (GPT-6 Astra leads) |
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. Kimi K3 256K: 52.0% of Kimi Allegretto (52.0% / 5h, 10.0% / 1w) per run. Its weekly limit holds about 5 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-6 Astra | Kimi K3 256K | Advantage |
|---|---|---|---|
| Capability | 74% | 34% | +40% (GPT-6 Astra leads) |
| Median task time | 2m 40s | 7m 33s | 4m 53s faster (GPT-6 Astra leads) |
| Approx. task cost | $0.046 / task | $0.233 / task | $0.187 / task lower (GPT-6 Astra leads) |
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. Kimi K3 256K: 13.2% of Kimi Allegretto (13.2% / 5h, 2.6% / 1w) per good solve. Its weekly limit holds about 5 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-6 Astra or Kimi K3 256K?
Kimi K3 256K clears higher: tier 4 of 5 versus tier 2 for GPT-6 Astra on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-28.
Which is cheaper per task, GPT-6 Astra or Kimi K3 256K?
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). Kimi K3 256K used 31% of Kimi Allegretto's weekly limit per pass, $0.146 per task at the listed price. Per task, GPT-6 Astra is about 2.7x cheaper ($0.053 vs $0.146).
What do GPT-6 Astra and Kimi K3 256K cost a month?
GPT-6 Astra runs on ChatGPT Plus at $20/month (public price as of 2026-07-20). Kimi K3 256K runs on Kimi Allegretto at $39/month (public price as of 2026-07-20).