zai API

What it is. The Z.ai API is Zhipu AI’s international platform serving the GLM family through an OpenAI-compatible Chat Completions endpoint, with Responses and Anthropic Messages protocols on GLM-5.3. Why it matters. It is the international distribution path for GLM-5.3 and GLM-5.3-Flash, the latter at a budget-tier $0.15/$0.50 per 1M tokens. Key characteristics. Three protocol surfaces (Chat Completions, Responses, Anthropic Messages) plus a dedicated coding-plan endpoint; tool_stream: true for tool streaming (recommended for Flash models); 1M-token context. What a professional should know. The China platform (BigModel, open.bigmodel.cn) is operated separately, and the rate-limit documentation page was not located (docs.z.ai paths 404) — a gap to verify before production use.

The Z.ai API (Zhipu’s international platform) serves the GLM family via an OpenAI-compatible Chat Completions endpoint at https://api.z.ai/api/paas/v4/chat/completions. GLM-5.3 additionally supports the OpenAI Responses protocol (base https://api.z.ai/api/v1) and the Anthropic Messages protocol (base https://api.z.ai/api/anthropic); the GLM Coding Plan uses https://api.z.ai/api/coding/paas/v4.

Authentication is a Bearer API key. Streaming is supported, with tool_stream: true for tool-streaming (recommended for Flash models). The China platform (BigModel, open.bigmodel.cn) is operated separately.

Why it matters

The Z.ai API matters as the multi-protocol surface for open-weight GLM models: it is one of the few tracked APIs exposing OpenAI, Anthropic and a coding-plan endpoint from a single provider, which lowers migration cost for teams that want both general and coding access to the same GLM-5.3 family. The cost trade-off is favorable at the flash tier ($0.15/$0.50) and moderate at the flagship ($1.40/$4.40), while the documented gap — no located rate-limit page — is an operational uncertainty. China AI Hub analysis indicates the API’s structural role is the international, protocol-flexible entry to Zhipu’s open model family, with the BigModel split meaning China and international are managed as separate surfaces.

Labels used above: Official fact (from Z.ai Quick Start and GLM-5.3 docs), Vendor-reported claim (pricing and capability statements by Zhipu AI), and China AI Hub analysis (our synthesis, always introduced as such).