Parameter mapping

The gateway speaks the OpenAI chat-completions wire format to every provider. OpenAI-compatible targets (OpenAI, Azure OpenAI, self-hosted vLLM and other custom OpenAI-compatible endpoints) bypass the policy on this page entirely: the request body is forwarded byte-for-byte apart from the gateway-only drop_tuning_params field, which is consumed before forwarding, so whatever the provider accepts, you get. For the translated lanes (Anthropic, Bedrock, Gemini, Vertex) the gateway builds the provider-native request itself, and every parameter follows an explicit policy:

mapped: translated faithfully to the provider’s native field.
dropped: a tuning parameter with no equivalent on the lane. By default it is removed, the request proceeds, and the drop is signaled (see below). It is never silently ignored.
refused: the request depends on the parameter functionally; honoring the request without it would change what you observably get. These always fail with a clear 400 unsupported_parameter error naming the parameter, the lane, and why.

drop_tuning_params

Send "drop_tuning_params": false in the request body to opt into strict mode: any parameter the lane cannot map then refuses instead of dropping. The default is true. The field itself is consumed by the gateway and never reaches a provider.

{
  "model": "anthropic/claude-haiku-4-5",
  "messages": [{"role": "user", "content": "hi"}],
  "seed": 42,
  "drop_tuning_params": false
}

{
  "error": {
    "type": "unsupported_parameter",
    "code": "unsupported_parameter",
    "message": "refusing to drop 'seed' for anthropic/claude-haiku-4-5: drop_tuning_params is false and Anthropic has no sampling seed. Remove it, set drop_tuning_params to true, or use a model that supports it"
  }
}

Drop signals

When a parameter is dropped, the drop is visible in three places:

Response body: extra_fields.params_dropped lists the dropped parameter names (on streams, on the final usage-bearing chunk).
Response header: X-LangWatch-Params-Dropped carries the same list, comma separated.
Trace: the gateway span records langwatch.gateway.params_dropped.

The table

Parameter	anthropic	bedrock	gemini / vertex	Notes
`audio`	dropped	dropped	dropped
`frequency_penalty`	dropped	dropped	mapped
`function_call`	refused	refused	refused
`functions`	refused	refused	refused
`logit_bias`	dropped	dropped	dropped
`logprobs`	refused	refused	mapped
`metadata`	dropped	dropped	dropped
`modalities`	dropped	dropped	dropped
`n`	dropped	dropped	dropped	n: 1 passes; n > 1 is reduced to one completion and signaled
`parallel_tool_calls`	dropped	dropped	dropped
`prediction`	dropped	dropped	dropped
`presence_penalty`	dropped	dropped	mapped
`prompt_cache_key`	dropped	dropped	dropped
`prompt_cache_retention`	dropped	dropped	dropped
`reasoning_effort`	mapped	mapped	mapped	bedrock: mapped for Anthropic (thinking) and Nova; refused for other families; a customer VPC endpoint maps Anthropic only
`response_format`	mapped	mapped	mapped	anthropic: json_schema enforced; json_object refused (no parseable-JSON guarantee); bedrock: json_schema enforced; json_object refused (no parseable-JSON guarantee); a customer VPC endpoint enforces json_schema for Anthropic models only; gemini: json_object and json_schema both enforced
`safety_identifier`	dropped	dropped	dropped
`seed`	dropped	dropped	dropped
`service_tier`	dropped	dropped	dropped	anthropic: “auto” passes natively; other values dropped; bedrock: dropped (AWS validates a different enum); gemini: dropped
`stop`	mapped	mapped	mapped
`store`	dropped	dropped	dropped
`stream_options`	mapped	mapped	mapped
`temperature`	mapped	mapped	mapped
`tool_choice`	mapped	mapped	mapped	anthropic: none/auto/required/named mapped; named must exist in tools; allowed_tools refused; bedrock: none maps by removing tools (Converse has no none mode); named must exist in tools; allowed_tools refused; gemini: none/auto/required/named mapped; named must exist in tools; allowed_tools refused
`tools`	mapped	mapped	mapped
`top_logprobs`	refused	refused	mapped
`top_p`	mapped	mapped	mapped	anthropic: dropped with a signal when temperature is also set (Anthropic models reject the pair); bedrock: dropped with a signal when temperature is also set on Anthropic models (they reject the pair); other families take both
`user`	dropped	dropped	dropped
`verbosity`	dropped	dropped	dropped
`web_search_options`	dropped	dropped	dropped
any other key	dropped	dropped	dropped	vendor params with no mapping on translated lanes

reasoning_effort budgets

On lanes that map reasoning_effort to a thinking budget (Anthropic models without adaptive thinking, on both the anthropic and bedrock lanes), the budget is derived from your output cap: budget = 1024 + ratio x (max_tokens - 1024) with ratios minimal 0.025, low 0.15, medium 0.425, high 0.80, xhigh 0.92, max 1.0. Claude Opus and Sonnet 4.6+ use the provider’s adaptive thinking with your effort passed through (minimal maps to low). Gemini thinking models receive the effort natively. Thinking tokens count inside usage.completion_tokens.

Get Started

SDK Integration

Coding CLI Integrations

Virtual Keys & Budgets

Governance

Providers

Features

API Reference

Self-Hosting

Cookbooks

drop_tuning_params

Drop signals

The table

reasoning_effort budgets

​drop_tuning_params

​Drop signals

​The table

​reasoning_effort budgets

drop_tuning_params

Drop signals

The table

reasoning_effort budgets