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Model ID from List Models, costream/auto, costream/fusion, or a named router as router/<id>. A model that several hosts serve routes across them; a host’s own ID selects that host. Add :nitro, :floor or :exacto to rank its hosts by throughput, price or tool-call validity, :free to keep free hosts, or :thinking to keep hosts that reason; an unknown suffix is refused. A ~author/family-latest alias, such as ~z-ai/glm-latest, selects the newest model of that family.

Conversation messages with roles and content. User content may mix text, image and document (PDF) blocks for models whose input_modalities list them.

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object

Maximum generated output tokens, up to the model’s output cap (top_provider.max_completion_tokens in List Models). Through a named router it is a ceiling on the router’s own limit.

Return protocol-specific server-sent events.

Default: false

Client-defined function tools, which the application executes, and web_search_20250305 to turn on the model’s own search.

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object

Fallback models, tried in order when the one before fails before any output. Each must support the request’s tools, response format and reasoning settings.

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string

OpenRouter provider preferences. only, ignore and order take provider names or slugs, or an endpoint tag such as deepinfra/turbo. sort (price, throughput, latency or exacto, with partition model or none), allow_fallbacks, quantizations, max_price, preferred_min_throughput, preferred_max_latency, zdr and data_collection are honoured; zdr and data_collection can only narrow your workspace’s privacy settings. data_region (us, eu or a country code, or a list of them) routes only to endpoints documented as processing there, fallbacks included; it can narrow the workspace’s Data Region but never widen it, and a request no endpoint can serve is refused with 400 data_region_unavailable. require_parameters: true refuses a request whose sampling parameters the model does not support, or a named router does not let requests override, instead of dropping them. enforce_distillable_text and options are accepted but not honoured, and are named in the x-audiolab-ignored-provider-fields header.

auto-router (allowed_models, cost_quality_tradeoff) with costream/auto; fusion (analysis_models, preset, model); web (the model’s own web search); file-parser (pdf.engine: native, pdf-text or mistral-ocr; max_files); response-healing (repairs a non-streamed JSON answer); context-compression (middle-out).

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object

middle-out removes messages from the middle of a conversation until it fits the smallest context among the requested model and its fallbacks.

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string

Named routers only: the published revision to use. Without it, the router’s current revision applies.

Minimum 1 · Maximum 1000

Named routers match their conditions on these values as metadata.<key>. metadata.user_id also keeps a session’s route, like session_id.

flex (cheaper, slower) or priority (faster) on OpenAI and Gemini models with a reviewed price for that tier, charged at that tier’s rate; the response’s service_tier names the tier that served it. Elsewhere the tier is dropped and named in x-audiolab-dropped-params, or refused under provider.require_parameters. auto and default use the standard tier.

Values: "auto""standard_only""default""flex""priority"

Anthropic prompt caching: {"type": "ephemeral"} here caches the prompt up to the last message; the same marker on a text part, system block or tool sets a breakpoint, at most 4. Writes and reads are charged at the model’s cache rates and reported in usage. A one-hour ttl is sent as five minutes. OpenAI and Gemini cache automatically, so the marker is accepted and named in x-audiolab-dropped-params.

Keeps a session on one route: costream/auto reuses the model it chose (without session_id it recognises a conversation by its first messages), and a named router assigns the same A/B variant (without it, each request is assigned afresh).