Kimi K3.1 Pro explained: long-horizon coding, 3D creation, factuality and the upgrade from K3

The takeaway

Kimi K3.1 Pro is available. Kimi describes it as the first model in its K3.1 series, in the three-trillion-parameter class, with improvements targeting long-horizon coding, 3D creation and complex agent workflows. A Highspeed version is also offered.

For existing K3 users, two questions deserve testing: can longer tasks finish more reliably with the same tools and budget, and does work requiring extensive factual cross-checking need less manual repair? Treat Highspeed as a separate comparison for latency-sensitive workflows.

This article analyzes official documentation. TboxIO has not independently rerun these benchmarks or measured API latency. Information and prices were checked on October 24, 2026.

From writing code to delivering a project

The official examples span repository fixes, complete projects, games, interactive pages, 3D modeling and professional workflows across files and tools.

These tasks test sustained execution. A correct function does not establish that an agent can coordinate dependencies, edits, testing and delivery. A convincing render does not establish that geometry, materials and later edits meet the requirements.

For 3D work, the documented approach includes writing and running scripts for Blender, SolidWorks and Rhino. This is collaboration with professional software, not a claim that all modeling can happen without tools.

Official benchmarks and comparisons with K3

All numbers below are vendor-reported. A public benchmark name does not mean independent verification by TboxIO. Kimi Code Bench 3.0 Long-horizon is explicitly an internal evaluation.

Evaluation	K3.1 Pro	Comparison reported by Kimi	Interpretation
Terminal-Bench 4.0	65.7%	GPT-6 Astra 58.2%; Claude Opus 5.5 66.4%	Terminal tasks in the vendor’s comparison, not a universal coding ranking
Kimi Code Bench 3.0 Long-horizon, internal	61.2%	K3 55.95%	An increase of 5.25 percentage points on this internal test
Difficult factuality stress test: error rate per factual claim	6.85%	K3 23.35%	A decrease of 16.50 percentage points on deliberately challenging samples

The 0.7-percentage-point Terminal-Bench gap to Opus 5.5 is not a claim that every project is only “0.7% behind.” It also says nothing by itself about price, speed or other agent frameworks.

The internal long-horizon comparison is useful evidence about progress over K3, but it remains a vendor-created task set. Validate your own repository, toolchain and acceptance criteria.

Lower factual error rates are not everyday accuracy rates

The stress test uses de-identified conversations previously flagged by users for factual errors. It intentionally concentrates difficult cases. Its 6.85% result must not be rewritten as “93.15% accuracy in daily use.”

The documentation gives a separate measure: the proportion of answers containing at least one factual error was about 46.4% of the predecessor’s level. That is an answer-level measure, not a per-claim error rate.

Continue checking important numbers, dates and references across documents. The reported improvement is relevant, but it does not remove the need for verification.

What does a million-token context mean?

The pricing page lists a 1,048,576-token context window for the K3 series. This provides room for longer documents, larger repositories and multi-turn tool results.

Capacity is different from reliable retrieval. More input costs more and may introduce duplicate or conflicting material. Keep a clear file structure, sources and task boundaries rather than sending every document with every request.

Pro or Highspeed?

Kimi describes Highspeed as offering the same intelligence with approximately 2–3 times the output speed. This is a vendor statement, not our measurement or a guarantee that a whole task takes one-third as long.

Tools, external services, tests and retries also consume time. Compare initial waiting, output generation and end-to-end latency separately. Faster output may help little when external tools dominate the workflow.

API pricing: Pro is cheaper than K3; Highspeed is separate

The following prices are from the official Chinese pricing page, in RMB per million tokens (MTok), not US dollars or per million Chinese characters.

Model	Input	Output	Cache hit	Cache write: 5-minute TTL	Cache write: 1-hour TTL
kimi-k3.1-pro	¥13.00	¥68.00	¥1.30	¥13.00	¥26.00
kimi-k3.1-pro-highspeed	¥26.00	¥136.00	¥1.30	¥26.00	¥52.00
kimi-k3	¥20.00	¥100.00	¥2.00	¥20.00	¥40.00

On base rates alone, Pro input is 35% cheaper than K3 and output is 32% cheaper. Highspeed’s base input and output prices are twice Pro’s. The standard version’s discount should not be attributed to Highspeed.

For one million ordinary input tokens and 100,000 output tokens, excluding cache operations and other fees, the illustration is ¥19.80 for Pro, ¥39.60 for Highspeed and ¥30.00 for K3. This calculates prices for assumed usage; it does not predict task consumption.

Caching is not a blanket discount. K3 cache writes are billed separately by TTL, while hits use the hit price. The default TTL is five minutes; one hour is also available. Savings depend on repeated prefixes, reuse intervals and measured usage.

Integration details to check

• Thinking is always enabled. Reasoning effort supports low, high and max, defaulting to max; do not assume an old thinking-off option applies.
• Multi-turn and tool workflows must preserve the complete assistant message, not just the final text.
• Some sampling parameters, including temperature, are fixed. Review old settings before migration.
• Visual input has format restrictions. The guide does not support direct public image URLs; use its specified file or base64 formats.
• The guide currently says web search is being updated and is not recommended for production workflows in the near term.

Test message history, tool loops and output parsing in an isolated environment before increasing traffic.

Available API, planned weights

The guide says full model weights will be released by November 4. As of this article’s check, that is a release plan, not proof that weights are already downloadable. Verify the official repository, license and runtime requirements before deployment.

The API guide requires a recharge to unlock the flagship model, with a stated minimum of ¥10. The ¥15 voucher given to new users cannot be used for K3.1 Pro. These are API-platform rules and should be distinguished from Kimi membership or Kimi Code subscriptions.

Is upgrading worthwhile?

Compare long repository changes, editable 3D or interactive projects, and document work requiring claim-by-claim checks. Fix tools, reasoning effort, retries and acceptance rules; record completion rate, manual edits, total cost and elapsed time.

Our judgment is that Pro’s lower base prices and the reported improvement in long workflows are the most promising combination. Evaluate Highspeed separately: is less waiting worth the extra fee? A broad migration should follow evidence from your own work.

Sources

• Official K3.1 Pro overview and integration guide: capabilities, reported evaluations, reasoning, access and planned weights.
• Official Kimi API pricing: RMB prices, caching and context capacity.

Models, services and prices can change. Check current official documentation when integrating.