The short answer: Kimi K3.1 Pro for lower token cost and open weights, Opus 5.5 for Anthropic's platforms
Choose Kimi K3.1 Pro if token cost matters most, since its list price is half of Opus 5.5 for both input and output, or if you plan to run the model yourself once Moonshot releases the weights by November 4, 2026. Choose Claude Opus 5.5 if you build on Anthropic's API or its cloud partners. Coding benchmarks favour neither clearly: in Moonshot's own table Opus 5.5 leads Terminal-Bench 4.0 by 0.7 points and BenchCAD by 3.5 points.
What was compared and how
Task: using a frontier model through an API for coding agents, long documents and multi-step knowledge work. We compared the API models kimi-k3.1-pro on the Kimi API Platform and claude-opus-5-5 on the Claude API, not the Kimi or Claude consumer apps and their subscriptions.
Evidence: Moonshot AI's Kimi K3.1 Pro announcement and Kimi API pricing page, and Anthropic's Claude Opus 5.5 model page, what's new page and pricing page, all read on October 25, 2026. Benchmark figures are vendor-reported; AppFor.ai has not run either model, so nothing below is a measured result. Prices are per million tokens in US dollars before tax.
Compare the same criteria
Each criterion states what each vendor documents and what it means for the task. Where a vendor does not publish something, we write that it is not established.
- Token price. Kimi K3.1 Pro: $2 input and $10 output. Opus 5.5: $4 input and $20 output. What this means: at list prices the same workload costs half as much on Kimi K3.1 Pro before caching.
- Caching. Kimi K3.1 Pro: cached input $0.20, cache writes $2 for a 5-minute and $4 for a 1-hour lifetime, with caching applied automatically to repeated prefixes. Opus 5.5: cache hits $0.20, writes $5 for 5 minutes and $8 for 1 hour. What this means: cache reads cost the same; writes cost less on Kimi, which matters for agents that resend long system prompts.
- Context and output. Kimi K3.1 Pro: a 1,048,576-token context window; the maximum output length is not established from the pages we read. Opus 5.5: 1M tokens of context and 128K tokens of maximum output. What this means: both take very long inputs; check Kimi's output limit before generating long files.
- Coding results. Moonshot reports Terminal-Bench 4.0 scores of 65.7% for K3.1 Pro and 66.4% for Opus 5.5, and BenchCAD with tools of 92.7% versus 96.2%, citing Anthropic's system card for the Opus figures. What this means: on these vendor-reported tests the two are close on terminal work and Opus leads on CAD reconstruction; independent results are not established.
- Reasoning controls and compatibility. Kimi K3.1 Pro: Moonshot reports its benchmark runs at reasoning effort max. Opus 5.5: adaptive thinking is always on with an effort parameter, and forced tool use returns an error. What this means: requests copied from older Claude models may fail on Opus 5.5; test your tool-calling code first.
- Speed options. Kimi K3.1 Pro Highspeed: $4 input and $20 output, which Moonshot says runs 2 to 3 times faster. Opus 5.5: a fast mode on the Claude API and some cloud platforms, priced separately. What this means: both offer a faster tier at a higher price; measured latency is not established.
- Deployment and data. Kimi K3.1 Pro: Kimi API, Kimi apps and Kimi Code, with Zero Data Retention available to API customers and open weights promised by November 4. Opus 5.5: Claude API, Amazon Bedrock, Claude Models on Google Cloud and Claude in Microsoft Foundry. What this means: open weights allow self-hosting once released; Anthropic's model is reachable through major cloud providers.
Which fits your real work?
A coding agent that runs many long sessions a day. Kimi K3.1 Pro fits a fixed budget, because input and output cost half as much and cache writes are cheaper. Opus 5.5 fits if your agent already runs on Claude and the slightly higher Terminal-Bench score Moonshot reports for it matters to you; verify on your own tasks.
Reviewing a contract bundle of several hundred pages. Both accept around a million tokens. Opus 5.5 documents a 128K output limit, which helps if you need long structured reports; for Kimi, test long outputs first.
A company that must keep data inside its own infrastructure. Kimi K3.1 Pro is the candidate once the weights are released, subject to the licence terms, which are not established yet. Opus 5.5 is available only as a hosted model through Anthropic and its cloud partners.
Cost of getting the work done
Worked example at list prices, without caching: a job that reads 2 million tokens and writes 200,000 tokens costs $6 on Kimi K3.1 Pro (2 x $2 plus 0.2 x $10) and $12 on Opus 5.5 (2 x $4 plus 0.2 x $20). On Kimi K3.1 Pro Highspeed the same job costs $12.
Both providers bill pay as you go. Kimi says its API has no subscription plan and is separate from Kimi memberships. Prices exclude taxes, and tool use, search or fast mode can add charges. Total cost per finished task also depends on how many tokens each model spends on reasoning, which is not established for either model on your workload.
Try both on the same small task
Suggested comparison, not a test we have run: take a small bug from your own repository with a failing test, send both models the same prompt and files, and record tokens used and the cost each API reports.
- The failing test passes and no other test breaks.
- The patch touches only the files that need to change.
- The explanation names the actual cause, not just the symptom.
- Record input and output tokens, so cost per fixed bug can be compared, not just price per token.
What would change the choice
Check these conditions before you commit. For model details, see our Kimi K3 profile, which covers K3.1 Pro pricing, and our Claude Opus 5.5 profile.
- If you need to self-host, wait for the Kimi K3.1 Pro weights and check the licence.
- If your stack depends on forced tool use, Opus 5.5 returns an error for it; plan the migration.
- If you must buy through AWS, Google Cloud or Azure, Opus 5.5 is listed on all three.
- If a long generated output is essential, confirm Kimi's maximum output before choosing it.
Go to the source
Sources & further reading
Based on the official documentation below. Features and access can change; check the provider before making a decision.
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