Does Kimi K3.1 Pro Replaces Opus 5.5? (Full Comparison)

Kimi K3.1 Pro vs Claude Opus 5.5 on 13 long-horizon agentic coding tasks. Both models ran in the same Claude Code harness, with the same prompts, the same effort setting and the same grading scripts. Only the model string changed. Kimi K3.1 Pro is listed at half the price of Opus 5.5 ($2 / $10 per million input / output tokens vs $4 / $20). Across all 13 tasks it cost $45.91 against Opus's $83.46, about 55% of the bill, and between 28% and 93% depending on the task. The reason is caching: about 98% of everything both models read came from the cache, and cached tokens cost $0.20 per million on