2026-W38: Spec planning
Week 38 of 2026 graded 13 coding agents on spec planning. GPT-6 Astra leads with C+. The biggest move since W37 2026 is GPT-5.6 Terra, C to C-. Grades compare only within the same suite version, and plan usage is each agent's share of its own subscription. Every agent ran the same suite cut headless through its own tools.Measured
spec-planning@v1 - the suite key these grades compare within
Published suite snapshot for 13 graded agents, current through Sep 15, 2026.
Sorted by capability. Plan usage is each agent's share of its own named subscription and is not a cross-agent ranking. See the Spec planning methodology or each agent's scorecard for full context.
| Agent | Grade | Capability | Task time | Reliability | Plan usage |
|---|---|---|---|---|---|
| GPT-6 Astracodex-cli | C+ | 74.4% | 3m 29s | 100% | 5%/1wChatGPT Plus |
| Claude Fable 5.1claude-code | C+ | 73.5% | 5m 56s | 100% | 56%/5hClaude Max 5x |
| GPT-6.1 Solcodex-cli | C+ | 71.3% | 6m 17s | 100% | 5%/1wChatGPT Plus |
| Claude Opus 5.5claude-code | C+ | 70.6% | 5m 31s | 100% | 12%/5hClaude Max 5x |
| Grok 4.7grok-cli | C | 67.4% | 45m 1s | 100% | 10%/1wSuperGrok Plus |
| GPT-5.6 Terracodex-cli | C- | 59.0% | 2m 48s | 100% | 5%/1wChatGPT Plus |
| GPT-6 Lunacodex-cli | D+ | 53.6% | 2m 40s | 100% | 5%/1wChatGPT Plus |
| Kimi K3 256Kkimi-cli | D | 46.7% | 2m 22s | 100% | 44%/5hKimi Allegretto |
| Claude Sonnet 5.5claude-code | D | 45.8% | 3m 44s | 100% | 8%/5hClaude Max 5x |
| Gemini 3.8 Flashantigravity-cli | D | 44.9% | 2m 54s | 100% | 1.7%/1wGoogle AI Pro |
| Composer 2.5cursor-cli | D- | 41.5% | 1m 51s | 100% | 0.4%/1mCursor Pro |
| Claude Haiku 4.5claude-code | F | 23.9% | 2m 34s | 100% | 4%/5hClaude Max 5x |
| Gemini 3.1 Proantigravity-cli | F | 19.3% | 1m 52s | 100% | 1.0%/1wGoogle AI Pro |
This page publishes aggregate outcomes only. Task prompts and private checker logic never leave the benchmark. Follow this suite over time on Grades over time.