A free Kimi account. Opening kimi.ai needs nothing, but sending your first message asks you to sign in with a Google account or a phone number.
The sign-in window we saw asks for an account and nothing to pay. Kimi's paid plans (from $19 a month, checked October 23) cover its coding tools and API, not this chat.
Hands-on status: we opened kimi.ai signed out, confirmed K3.1 Pro as the default model, typed a task, and hit the sign-in wall at send on October 24. We didn't create an account, so steps after signing in are Kimi-documented, not tested by us.