We promoted the GLM 5.1 API to our production reasoning path — the outputs are consistent enough that we stopped babysitting them with retries.
The GLM 5.1 API is Z.ai's refined flagship GLM model — a polish of GLM-5 that keeps the frontier reasoning while tightening consistency, with native tool calling, structured outputs, and a long context window. The GLM 5.1 API is OpenAI-compatible: point any existing SDK at RouterBase and set the model to glm-5-1. Input at $1.26 / 1M tokens, output at $3.96 / 1M tokens — 10% below the official rate, all through one REST endpoint.
Input
GLM-5.1
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GLM 5.1 API: Chat
Use the GLM 5.1 API to run Z.ai's refined flagship — GLM-5.1 sharpens GLM-5's reasoning and tightens consistency, so high-stakes prompts come back right the first time.
The GLM 5.1 API is Z.ai's refined flagship — a polish of GLM-5 that keeps the frontier reasoning while tightening consistency, with native tool calling, structured outputs, and a long context window. Routed through RouterBase, the GLM 5.1 API is fully OpenAI-compatible: point any existing SDK at RouterBase's base URL, set the model to glm-5-1, and your first GLM 5.1 API call goes through immediately.
Pricing for the GLM 5.1 API is $1.26 / 1M input and $3.96 / 1M output — 10% below the official rate, via one RouterBase key (no Z.ai account).
Six reasons teams ship on the GLM 5.1 API
From dependable, consistent answers to a 10%-off price — what sets the GLM 5.1 API apart.
Consistent, not just capable
GLM-5.1 is a refinement of GLM-5 — the same frontier reasoning, with steadier outputs and fewer off-runs, so the quality you see in testing is the quality you ship.
Dependable on hard tasks
Hand the GLM 5.1 API your gnarliest reasoning, analysis, or coding problems — it stays accurate and well-structured where lighter models wobble.
Native tool calling
GLM-5.1 drives multi-step tool use in the OpenAI format with consistent judgment — agents behave the same way run after run, not just on a good day.
Long context window
The GLM 5.1 API takes long inputs — fit big documents, full codebases, or an entire agent session into one call without losing the thread.
OpenAI-compatible, one key
The GLM 5.1 API uses the OpenAI chat-completions format, so one RouterBase key swaps GLM-5.1 in beside GPT-5.5, Claude, Gemini, and 200+ other models.
10% off the list price
GLM-5.1 runs 10% under Z.ai's published rate — $1.26 / 1M input, $3.96 / 1M output. Top-tier consistency, billed per token, nothing per request.
Quickstart
Get started with the GLM 5.1 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 GLM-5.1 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 glm-5-1. Streaming, tool calls, and structured outputs all follow the standard chat-completions schema.
Inspect usage
Every GLM 5.1 API response returns a token breakdown — input and output — so 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 GLM 5.1 API
Real production loads running on the RouterBase model catalog across 200+ models.
GLM-5.1 gives us the same answer quality every run through RouterBase — that predictability is what let us ship it to customers.
Our agents behave consistently on the GLM 5.1 API run after run — the variance that used to break long workflows is basically gone.
We A/B the GLM 5.1 API against GPT and Claude behind one RouterBase key — it matches their quality on our evals at a lower token price.
Pointing our OpenAI SDK at the GLM 5.1 API took one base-URL change, and the answers have been steady ever since.
Structured outputs on the GLM 5.1 API come back clean every time — we parse straight into our pipeline with zero cleanup.
Swapped my OpenAI base URL to the GLM 5.1 API and the quality held up — fewer weird answers than the cheaper models I tried.
On our hardest eval set the GLM 5.1 API is the most consistent model we tested — not just the smartest on a good day.
Per-token billing plus consistent GLM 5.1 API output means predictable cost and predictable quality — both matter at our scale.
Frequently Asked Questions
Common questions about the GLM 5.1 API.
The GLM 5.1 API is RouterBase's pass-through to Z.ai's GLM-5.1 — a refined GLM-5 that keeps the frontier reasoning while improving consistency, served over an OpenAI-compatible REST interface with native tool calling and structured outputs.