We send our hardest reasoning to the Kimi K2 Thinking API — the step-by-step thinking solves cases our direct model kept missing.
The Kimi K2 Thinking API is Moonshot AI's open-weight Kimi K2 reasoning model — extended chain-of-thought for hard reasoning, math, and agentic tasks, with native tool calling, structured outputs, and a long context window. The Kimi K2 Thinking API is OpenAI-compatible: point any existing SDK at RouterBase and set the model to kimi-k2-thinking. Input at $0.51 / 1M tokens, output at $2.125 / 1M tokens — 15% below the official rate, all through one REST endpoint.
Input
Kimi K2 Thinking
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Kimi K2 Thinking API: Chat
Use the Kimi K2 Thinking API to run Moonshot AI's reasoning model — Kimi K2 Thinking works through problems step by step with extended chain-of-thought, for the hardest reasoning, math, and agentic tasks, open-weight.
The Kimi K2 Thinking API is Moonshot AI's open-weight Kimi K2 reasoning model — it works through problems with extended chain-of-thought for hard reasoning, math, and agentic tasks, with native tool calling, structured outputs, and a long context window. Routed through RouterBase, the Kimi K2 Thinking API is fully OpenAI-compatible: point any existing SDK at RouterBase's base URL, set the model to kimi-k2-thinking, and your first Kimi K2 Thinking API call goes through immediately.
Pricing for the Kimi K2 Thinking API is $0.51 / 1M input and $2.125 / 1M output — 15% below the official rate, via one RouterBase key (no Moonshot AI account).
Six reasons teams ship on the Kimi K2 Thinking API
From deep, step-by-step reasoning to a 15%-off price — what sets the Kimi K2 Thinking API apart.
Thinks before it answers
Kimi K2 Thinking spends test-time compute reasoning through a problem — extended chain-of-thought that cracks multi-step math, logic, and planning where direct models guess.
Reasoning-grade coding & agents
The Kimi K2 Thinking API reasons across long tool chains — it plans, self-corrects, and works through complex coding and agentic tasks instead of one-shotting them.
Native tool calling
The Kimi K2 Thinking API calls tools in the OpenAI format and reasons between calls — Kimi K2 was built for tool use, so thinking agents drop in without custom glue.
Long context window
The Kimi K2 Thinking API takes a long context — fit whole codebases, long documents, or a full reasoning trajectory into one call.
OpenAI-compatible, one key
The Kimi K2 Thinking API uses the OpenAI chat-completions format, so one RouterBase key swaps Kimi K2 Thinking in beside GPT-5.5, Claude, Gemini, and 200+ other models.
15% off the list price
Kimi K2 Thinking runs 15% under Moonshot AI's published rate — $0.51 / 1M input, $2.125 / 1M output. Frontier-grade reasoning at open-weight prices, billed per token.
Quickstart
Get started with the Kimi K2 Thinking API in 3 steps
From sign-up to your first response in under 5 minutes.
Create a RouterBase API key
Sign up and create an API key — it reaches Kimi K2 Thinking and every other model in the RouterBase catalog from one account.
Send your first message
Point any OpenAI-compatible SDK at routerbase.com/v1 and set the model to kimi-k2-thinking. Streaming, tool calls, and structured outputs all follow the standard chat-completions schema.
Inspect usage
Every Kimi K2 Thinking API response returns a token breakdown — input and output — so reasoning cost stays visible on every call.
Pay only for what you use
RouterBase passes through partner-tier pricing. Compared against the model's official published API rate.
What teams build with the Kimi K2 Thinking API
Real production loads running on the RouterBase model catalog across 200+ models.
Kimi K2 Thinking is our model for complex planning through RouterBase — it reasons through the whole task instead of guessing the first step.
Our agents reason between tool calls on the Kimi K2 Thinking API — fewer dead ends on long multi-step jobs.
We A/B the Kimi K2 Thinking API against frontier reasoners behind one RouterBase key — it holds up on our math and logic evals for far less.
Switching our hard prompts to the Kimi K2 Thinking API was one base-URL change, and the answers came back actually worked-through.
Multi-step refactors got more reliable once we routed them to the Kimi K2 Thinking API — it plans the change before writing it.
For the gnarly stuff I reach for the Kimi K2 Thinking API — open weights, real reasoning, and cheap enough to let it think.
On our toughest eval set the Kimi K2 Thinking API is the best reasoning value we tested — frontier-ish at open-model cost.
Per-token billing keeps the Kimi K2 Thinking API affordable even when it spends tokens reasoning — we budget for the hard requests.
Frequently Asked Questions
Common questions about the Kimi K2 Thinking API.
The Kimi K2 Thinking API is RouterBase's pass-through to Moonshot AI's Kimi K2 Thinking — the open-weight Kimi K2 reasoning model that works through problems with extended chain-of-thought, served over an OpenAI-compatible REST interface with native tool calling and structured outputs.