Model · Z.ai

Z.ai GLM 5.3 Flash

Z.ai GLM 5.3 Flash is served by Z.ai through OpenRouter. It provides 1.05M tokens of context and supports text, vision, video inputs.

Snapshot 2026-10-16 z-ai/glm-5.3-flash Formerly known as OX Alpha

Context window

1.05M tokens

Input / 1M tokens

$0.150

Output / 1M tokens

$0.500

Key facts

Provider	Z.ai
OpenRouter ID	`z-ai/glm-5.3-flash`
Modalities	Text, Vision, Video
Best for	Budget, Long Context, Multimodal

Source openrouter.ai/api/v1/models Verified 2026-10-16 Drift-checked daily 06:00 CST

Best-fit workloads

Best for long context

Large context window for documents and transcripts.

Best for budget

Low input/output cost for high-volume workloads.

Best multimodal

Handles images, files, audio or video inputs.

Cost estimates

These examples use the 2026-10-16 input and output prices. Cache discounts, provider surcharges and tool fees are excluded.

Workload	Input	Output	Estimated cost
Quick test	20,000	5,000	$0.005
Product chat month	500,000	125,000	$0.138
Document batch	5,000,000	1,000,000	$1.25

Strengths

✓ Mid-tier pricing that undercuts the frontier models by a wide margin
✓ 1M-token window — large, though no longer the largest in this snapshot
✓ Useful for bulk document processing and multimodal extraction

Limitations

! Reasoning depth may trail frontier models
! Vendor-specific tool behavior should be tested before production

OpenRouter API quickstart

Run these examples from your server or edge function. Keep the OpenRouter API key private and do not expose it in browser code.

cURL

curl https://openrouter.ai/api/v1/chat/completions \
  -H "Authorization: Bearer $OPENROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "z-ai/glm-5.3-flash",
    "messages": [{ "role": "user", "content": "Summarize this document in five bullet points." }],
    "max_tokens": 500
  }'

JavaScript / TypeScript

const response = await fetch("https://openrouter.ai/api/v1/chat/completions", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.OPENROUTER_API_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    model: "z-ai/glm-5.3-flash",
    messages: [{ role: "user", content: "Summarize this document in five bullet points." }],
    max_tokens: 500,
  }),
});

const data = await response.json();
console.log(data.choices[0].message.content);

How to evaluate Z.ai GLM 5.3 Flash

Run five real tasks from your product, not generic demo prompts.
Record token usage, latency and output quality.
Estimate cost using your real input/output mix.
Compare it against one model with a similar price and one stronger model.

Compare models View on OpenRouter ↗

Z.ai GLM 5.3 Flash FAQ

What is Z.ai GLM 5.3 Flash?

Z.ai GLM 5.3 Flash is a Z.ai model available through OpenRouter. It supports text, vision, video inputs and is suited for budget, long context, multimodal workloads.

How much does Z.ai GLM 5.3 Flash cost on OpenRouter?

The 2026-10-16 snapshot lists $0.150 per 1M input tokens and $0.500 per 1M output tokens. Verify current pricing on OpenRouter before production.

How large is Z.ai GLM 5.3 Flash's context window?

Z.ai GLM 5.3 Flash offers 1.05M tokens of context in the current snapshot. Provider-specific limits and surcharges may apply.

Head-to-head comparisons

DeepSeek V4 Flash vs Z.ai GLM 5.3 Flash

Since the 2026-09-22 repricing this is a read-versus-write decision rather than a cheaper-versus-dearer one. DeepSeek V4 Flash wins on anything that reads a lot and writes a little; GLM 5.3 Flash wins on mixed-media input and on generation.

Xiaomi MiMo-V2.5 vs Z.ai GLM 5.3 Flash

GLM 5.3 Flash is still the pick when the document genuinely needs more than a million tokens of window. MiMo-V2.5 is now the cheaper of the two for everything else, and the only one of the pair that takes audio.

Union Alpha vs Z.ai GLM 5.3 Flash

Pick Pareto only when something else about it wins your evaluation — it is roughly fifteen times the price per token, and since the 2026-09-22 repricing GLM 5.3 Flash is cheaper on both directions than it was. Both now have a named vendor, so the anonymity that made Union Alpha hard to recommend is gone.

Pricing and context data are based on a 2026-10-16 snapshot. Provider limits can change; always verify on OpenRouter before production.

Z.ai GLM 5.3 Flash is the model that was released anonymously as OX Alpha. That release, and every other one like it, is documented in the stealth models register — see the archive for the timeline of the reveal. The line's most recent codename, Union Alpha, has since been revealed as Unbiased Pareto too — so there is no anonymous release on OpenRouter at the moment.