Verdict: for money, Kimi K3.1 Pro is now the better terminal-coding agent for most developers, and Claude Opus 5.5 keeps the crown only if your team is already locked into Anthropic tooling. Moonshot released Kimi K3.1 Pro on October 23, 2026, and its own comparisons show an open-weight model one rung short of the strongest proprietary flagship (Moonshot AI). The decision is not a benchmark; it is a deadline. Full model weights are promised by November 4, 2026 (Moonshot AI), and after that date the same capability becomes self-hostable, which no closed frontier model offers. Here is the call split by situation, before that drop.
TL;DR
- K3.1 Pro scores 65.7% on Terminal-Bench 4.0 against Opus 5.5's 66.4% and GPT-6 Astra's 58.2% on Moonshot's own table (Moonshot AI).
- An independent Artificial Analysis run measured 67% and called it the highest score of any model, so the two harnesses disagree on the winner (Fello AI, Artificial Analysis).
- API list rates are $2 per million input tokens and $10 per million output on the Kimi API, versus $4 and $20 for Opus 5.5 (Moonshot, Anthropic).
- Last verified: November 1, 2026.
Is Kimi K3.1 Pro a real upgrade over Kimi K3?
Yes, and the upgrade is concentrated exactly where coding agents live. K3.1 Pro is a post-trained version of K3 with substantially larger post-training compute, spanning coding, 3D creation, financial research, and long-horizon agentic work, with a 1-million-token context window (Moonshot AI). The launch post and launch summary put it at 2.8T total parameters with 104B active in a MoE layout, the same size class as K3 but priced about 33% below it (Fello AI). On Moonshot's internal Kimi Code Bench 3.0 Long-horizon, which is self reported, K3.1 Pro scores 61.2% against K3's 55.95% (Moonshot AI). A Highspeed variant ships in the same release and delivers 2-3x the output speed for double the per-token rate (Moonshot).
Kimi K3.1 Pro vs Claude Opus 5.5 on Terminal-Bench 4.0: who wins?
Nobody can honestly answer "definitely Kimi" or "definitely Claude", and the disagreement between the two measurement sets is this story's real hook. Moonshot's own table, run with the Claude-Code harness at reasoning effort max, scores K3.1 Pro 65.7%, Claude Opus 5.5 66.4%, and GPT-6 Astra 58.2% (Moonshot AI). That leaves an Opus margin of 0.7 points, inside the run-to-run noise that benchmark practitioners normally see between harnesses. Artificial Analysis's independent run of the same benchmark measured K3.1 Pro at 67%, and its launch commentary called that the highest score of any model, with its Intelligence Index placing K3.1 Pro at 55.1 against 57.6 for Opus 5.5 (Fello AI, Artificial Analysis). On the remaining published table, Opus 5.5 leads BenchCAD with tools, 96.2% to K3.1 Pro's 92.7% (HokAI).
| Benchmark | Kimi K3.1 Pro | Claude Opus 5.5 | GPT-6 Astra |
|---|---|---|---|
| Terminal-Bench 4.0 (Moonshot run) | 65.7% | 66.4% | 58.2% |
| Terminal-Bench 4.0 (Artificial Analysis run) | 67% | not re-published in this set | not re-published in this set |
| BenchCAD with tools | 92.7% | 96.2% | 95.9% |
| Model | Input /1M | Cached input /1M | Output /1M |
|---|---|---|---|
| Kimi K3.1 Pro | $2.00 | $0.20 | $10.00 |
| K3.1 Pro Highspeed | $4.00 | $0.20 | $20.00 |
| Claude Opus 5.5 | $4.00 | $0.20 | $20.00 |
| GPT-6 Astra (short context) | $10.00 | $1.00 | $50.00 |
Table sources: Kimi API rates (Moonshot), Opus 5.5 list pricing effective October 22, 2026 (Anthropic), and Astra rates (OpenAI).
What does Kimi K3.1 Pro cost next to Opus 5.5 and GPT-6 Astra?
At list rates the Kimi flagship now costs half of Opus 5.5 on fresh input and half on output, and Astra costs five times Kimi on input under OpenAI's short-context tier (Moonshot, Anthropic, OpenAI). Astra's published price doubles to $20 input and $75 output once a prompt crosses 272K input tokens, while Kimi and Anthropic bill their full 1M-token windows at the standard rate with no long-context surcharge (OpenAI, Axis Intelligence). As our analysis of the linked rates (our own arithmetic on the vendor list prices, not a lab measurement), before first-pass cache writes: a coding session that reads 160,000 tokens with 90% cache hits and writes 5,000 output tokens costs about $0.11 on K3.1 Pro, about $0.19 on Opus 5.5, and about $0.55 on GPT-6 Astra short-context (Moonshot, Anthropic, OpenAI). Kimi's cached-input rate matches Opus's $0.20, which is why long-context agentic loops keep Kimi's advantage smaller than half: shared cache economics absorb part of the gap (Moonshot, Anthropic).
Should you switch before the Nov 4 weights drop?
For API-first teams, switch the coding workload now: the benchmark tie plus the 2x list-rate discount makes K3.1 Pro the rational default, and Moonshot documents a run-eval on your own tasks first because thinking-token volume differs per task (AIHubMix). For Opus-committed teams, stay put: the 0.7-point margin on Moonshot's harness and the BenchCAD lead are Anthropic's strongest published case, and Anthropic's recommended default guidance still names Opus 5.5 for most workloads (Anthropic). For self-hosters, the calendar matters more than the benchmark: after November 4 the weights permit in-house serving, which converts the floor of $10 per million output tokens into the cost of GPUs you already own (Moonshot AI). For GPT-6 Astra buyers, the honest comparison is price: Astra publishes $10 and $50 against Kimi's $2 and $10 with no Terminal-Bench edge in Moonshot's table (OpenAI, Moonshot AI). One access note: Kimi Enterprise administrators must enable K3.1 Pro, as access is off by default at launch (Moonshot AI).
FAQ
Q: When do the Kimi K3.1 Pro open weights drop?
A: Moonshot has promised the full model weights by November 4, 2026, per its launch post (Moonshot AI).
Q: Is Kimi K3.1 Pro better than Claude Opus 5.5 on Terminal-Bench 4.0?
A: On Moonshot's own table, Opus leads by 0.7 points, 66.4% to 65.7%; on Artificial Analysis's independent run, Kimi measured 67% and ranked first (Moonshot AI, Artificial Analysis).
Q: How much does Kimi K3.1 Pro cost on the Kimi API?
A: $2 per million input tokens, $10 per million output tokens, and $0.20 per million cached input tokens; the Highspeed variant bills $4 and $20 (Moonshot).
Q: Should small engineering teams self-host the weights after November 4?
A: If you already run GPU capacity and your workload is steady, the November 4 weights make self-hosting economically sensible for the first time at this capability level; otherwise the metered API remains the low-commitment route (Moonshot AI).
Sources and verification
Primary: Moonshot AI launch post and Kimi API rate page. Independent measurement: Artificial Analysis run as quoted by Fello AI. Corroboration: Lyceum model index, HokAI, AIHubMix cost analysis. Competitor rates: Anthropic Opus 5.5 and the Anthropic list-price PDF, plus OpenAI pricing docs. Related reading: Kimi K3 vs Claude Fable 5, four-way 2026 comparison, GPT-6 Astra vs Claude Fable 5.1, open-source coding LLM update, best AI agent for coding. Our methodology: how we work. Corrections are logged there. This article was drafted with AI assistance and verified by a human editor.
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