Claude Sonnet 5.5 vs Kimi K3 256K
Claude Sonnet 5.5 leads overall, C- to D+. Claude Sonnet 5.5 is about 51x cheaper per task. By suite, real-world issues is even at C- and Claude Sonnet 5.5 takes spec planning (C+ to C-). The data gives no reason to pick Kimi K3 256K over Claude Sonnet 5.5 this week.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 Claude Sonnet 5.5
Claude Sonnet 5.5 leads overall, C- to D+. By suite: real-world issues is even at C- (60% vs 60% capability); Claude Sonnet 5.5 takes spec planning, C+ to C- (74% vs 56% capability); Claude Sonnet 5.5 takes vibe coding, D+ to F (48% vs 34% capability). Claude Sonnet 5.5 used <1% of Claude Max 5x's weekly limit per pass, $0.003 per task at the listed price. Kimi K3 256K used 31% of Kimi Allegretto's weekly limit per pass, $0.146 per task at the listed price. Per task, Claude Sonnet 5.5 is about 51x cheaper ($0.003 vs $0.146). Claude Sonnet 5.5 is faster on real-world issues: a median task takes 37s against 3m 31s. Both finished every task on it. The data gives no reason to pick Kimi K3 256K over Claude Sonnet 5.5 this week.
Changed since W39: 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 | Claude Sonnet 5.5 | Kimi K3 256K | Advantage |
|---|---|---|---|
| Capability | 60% | 60% | Even |
| Median task time | 37s | 3m 31s | 2m 54s faster (Claude Sonnet 5.5 leads) |
| Approx. task cost | $0.002 / task | $0.126 / task | $0.124 / task lower (Claude Sonnet 5.5 leads) |
Claude Sonnet 5.5: 4.0% of Claude Max 5x (4.0% / 5h) per run. Its weekly limit holds about 13.8 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.
Work per window: Claude Sonnet 5.5 3653 vs Kimi K3 256K 140 suite runs per month (Claude Sonnet 5.5 leads); per plan-dollar: 36.52 vs 3.60 (Claude Sonnet 5.5 leads). Work figures compare outputs, so unlike quota shares they are comparable across plans.
| Dimension | Claude Sonnet 5.5 | Kimi K3 256K | Advantage |
|---|---|---|---|
| Capability | 74% | 56% | +18% (Claude Sonnet 5.5 leads) |
| Median task time | 3m 25s | 5m 26s | 2m 1s faster (Claude Sonnet 5.5 leads) |
| Approx. task cost | $0.007 / task | $0.224 / task | $0.217 / task lower (Claude Sonnet 5.5 leads) |
Claude Sonnet 5.5: 4.0% of Claude Max 5x (4.0% / 5h) per run. Its weekly limit holds about 13.8 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.
Work per window: Claude Sonnet 5.5 3653 vs Kimi K3 256K 281 suite runs per month (Claude Sonnet 5.5 leads); per plan-dollar: 36.52 vs 7.20 (Claude Sonnet 5.5 leads). Work figures compare outputs, so unlike quota shares they are comparable across plans.
| Dimension | Claude Sonnet 5.5 | Kimi K3 256K | Advantage |
|---|---|---|---|
| Capability | 48% | 34% | +14% (Claude Sonnet 5.5 leads) |
| Median task time | 56s | 7m 33s | 6m 36s faster (Claude Sonnet 5.5 leads) |
| Approx. task cost | $0.001 / task | $0.233 / task | $0.232 / task lower (Claude Sonnet 5.5 leads) |
Claude Sonnet 5.5: 0.2% of Claude Max 5x (0.2% / 5h) per good solve. Its weekly limit holds about 13.8 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.
Work per window: Claude Sonnet 5.5 73050 vs Kimi K3 256K 1107 good solves per month (Claude Sonnet 5.5 leads); per plan-dollar: 730.50 vs 28.38 (Claude Sonnet 5.5 leads). Work figures compare outputs, so unlike quota shares they are comparable across plans.
Grades and deltas are comparable only within a suite version. See methodology.
Frequently asked questions
Which is better for coding, Claude Sonnet 5.5 or Kimi K3 256K?
They are even on our ladder: both clear tier 4 of 5 at 60% capability on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-28.
Which is cheaper per task, Claude Sonnet 5.5 or Kimi K3 256K?
Claude Sonnet 5.5 used <1% of Claude Max 5x's weekly limit per pass, $0.003 per task at the listed price. Kimi K3 256K used 31% of Kimi Allegretto's weekly limit per pass, $0.146 per task at the listed price. Per task, Claude Sonnet 5.5 is about 51x cheaper ($0.003 vs $0.146).
Which gives more coding work per dollar, Claude Sonnet 5.5 or Kimi K3 256K?
Claude Sonnet 5.5 delivers more benchmark work per subscription dollar: 36.52 suite runs per plan-dollar versus 3.60 for Kimi K3 256K (at $100/month priced 2026-07-20, and $39/month priced 2026-07-20). Work figures compare outputs, so unlike raw quota shares they are comparable across plans.
What do Claude Sonnet 5.5 and Kimi K3 256K cost a month?
Claude Sonnet 5.5 runs on Claude Max 5x at $100/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).