Z.ai: GLM 5.3 FlashX

POST/v1/chat/completions

GLM-5.3-FlashX is the high-speed tier of Z.ai's GLM-5.3-Flash, documented together with Flash and delivering inference speeds of up to 200 tokens per second. It shares Flash's native multimodal design and hybrid sparse-plus-linear attention, with image, video and file input, always-on reasoning, tool calling and structured output. Pick it over standard Flash for latency-sensitive coding agents, GUI and browser tasks, and interactive chat.

Request body

Parameters supported by this model. Values, defaults, and limits are read from the model registry.

stringmodelrequired

Model identifier. Set to z-ai/glm-5.3-flashx.

Default: z-ai/glm-5.3-flashx

array<object>messagesrequired

Conversation messages in system, user, or assistant order.

Optional<integer>max_tokens

Maximum number of tokens the model may generate in the response.

Maximum: 131072

Optional<number>temperature

Sampling temperature. Lower values are more deterministic; higher values are more creative.

Range: 0 to 2

Default: 1

Optional<number>top_p

Nucleus sampling threshold. Use this or temperature, but usually not both.

Range: 0 to 1

Optional<boolean>stream

When true, returns incremental Server-Sent Events instead of one completed response.

Default: false

Optional<array>tools

Tool definitions that the model may call during the response.

Optional<string>tool_choice

Controls whether the model may call a tool and, when supported, which tool it must call.

Optional<object>response_format

Controls the response format, including JSON mode or structured JSON output when supported.

Optional<array<string>>stop

Sequences that stop generation when the model produces one of them.

Optional<number>presence_penalty

Penalizes tokens that already appeared, encouraging the model to introduce new topics.

Range: -2 to 2

Optional<number>frequency_penalty

Penalizes repeated tokens, reducing repetition in the generated response.

Range: -2 to 2

Optional<integer>seed

Seed used to make sampling more reproducible when the provider supports it.

Optional<string>reasoning_effort

Request parameter supported by this model.

Allowed values: low, high, max

Default: max

Optional<integer>top_k

Request parameter supported by this model.

Minimum: 0

Response Schema

Fields returned by this model API response.

array<object>choicesrequired

Generated completion choices.

stringidrequired

Unique chat completion identifier.

stringmodelrequired

Model that generated the response.

Optional<object>usage

Token usage when available.

Model capabilities

array<string>capability_tagsrequired

Capabilities declared by the model registry.

Default: chat, vision, reasoning, structured_output, function_calling

integercontext_lengthrequired

Maximum context window accepted by this model.

Default: 1048576 tokens

stringexecution_moderequired

Execution mode declared by the model registry.

Default: sync

curl -X POST https://api.sandbase.ai/v1/chat/completions \
  -H "Authorization: Bearer $SANDBASE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "z-ai/glm-5.3-flashx",
  "messages": [
    {
      "role": "user",
      "content": "Describe this product in one sentence."
    }
  ]
}'

Response200 OK

{
  "id": "chatcmpl_abc123",
  "model": "z-ai/glm-5.3-flashx",
  "choices": [
    {
      "message": {
        "role": "assistant",
        "content": "A concise product description."
      }
    }
  ]
}