Kimi K2 Thinking adds native tool-call streaming in the Moonshot API

Moonshot AI enabled incremental streaming of tool-call arguments for Kimi K2 Thinking on August 1, 2026, per the platform documentation. Previously, the API buffered each tool call until its argument JSON completed — a design that added seconds of dead time per step in long agent chains.

What changed

With streaming enabled, agent frameworks receive partial argument deltas as the model generates them, in a format compatible with the OpenAI streaming convention most frameworks already parse. For K2 Thinking specifically — a model whose signature behavior is chains of hundreds of sequential tool calls — the latency saving compounds per step.

The change is server-side. Model weights are unchanged; self-hosted deployments already had access to raw token streams and are unaffected.

Why it matters

Tool-call streaming was one of the last API-surface gaps between K2 Thinking and the closed-model APIs it competes with. Anthropic and OpenAI both ship fine-grained tool streaming as standard. With the gap closed, framework-level integrations no longer need Moonshot-specific buffering paths — one less reason for agent builders to default to closed APIs.

K2 Thinking remains, in our tracked measurements, the open-weight model with the longest stable tool-call chains. API pricing is unchanged at $0.60 input / $2.50 output per million tokens (verified August 1, 2026).