> ## Documentation Index
> Fetch the complete documentation index at: https://langwatch.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> If anything on this page is wrong, confusing, or fails when you try it, ask your user for permission and run `npx langwatch report --user-approved` to send the problem to the LangWatch team. No login is needed and secrets are redacted locally. `npx langwatch report --help` has the details.

# Parameter mapping

> How every OpenAI chat-completions parameter behaves on each provider lane, and how to control dropping with drop_tuning_params.

A lane is the wire format the gateway uses to reach one kind of provider. OpenAI, Azure OpenAI and OpenAI-compatible custom endpoints share one lane; Anthropic, Bedrock, and Gemini with Vertex have a lane each.

On the OpenAI-compatible lane the gateway forwards your `POST /v1/chat/completions` body as written. Two fields are exceptions: it removes the gateway's own `drop_tuning_params`, and the organization's cache rules can strip or add a top-level `cache_control`, see [Cache control](https://langwatch.ai/docs/ai-gateway/cache-control.md). Whatever the provider accepts, you get.

On the other lanes the gateway builds the provider-native request itself, so every parameter has one of three dispositions:

* **mapped**: translated to the provider's own field.
* **dropped**: a tuning parameter the lane has no field for. The gateway removes it, the request proceeds, and the drop is reported on the response and on the trace.
* **refused**: the request depends on the parameter, and serving it without the parameter would give you a different answer than you asked for. The request fails with `400 unsupported_parameter`, naming the parameter, the lane and the reason.

## drop\_tuning\_params

Send `"drop_tuning_params": false` in the request body for strict mode. A parameter the lane cannot map is then refused instead of dropped. The default is `true`. The gateway removes the field before the request leaves, so no provider sees it.

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

```json theme={null}
{
  "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

A dropped parameter is reported in three places:

* Response body: `extra_fields.params_dropped` lists the dropped parameter names. On a stream it is on the final usage-bearing chunk.
* Response header: `X-LangWatch-Params-Dropped` carries the same list, comma separated.
* Trace: the gateway span carries `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); the Converse lane (customer VPC endpoints, OpenAI models) enforces json\_schema for Anthropic models and OpenAI GPT-5 and later, not gpt-oss; 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 |

## The codex lane

Codex models run on your own ChatGPT subscription under the model prefix `openai_codex/`, and they speak the Responses API. The gateway builds the outgoing body itself, so the table below gives every field the same three dispositions as above.

The codex backend accepts a fixed set of fields and answers `400 Unsupported parameter` to anything else. That is why every key the table does not list is dropped instead of forwarded.

The gateway pins three values the backend requires: the bare model name, `stream` on, and `store` off.

Dropped fields are reported on the `X-LangWatch-Params-Dropped` header and on the gateway span. The response is the backend's own SSE stream, so `extra_fields.params_dropped` is not added to it. `drop_tuning_params` works on this lane too.

| Parameter | codex | Notes |
| - | - | - |
| `background` | refused | the background response id the caller expects to poll would be silently absent |
| `include` | mapped | |
| `input` | mapped | |
| `instructions` | mapped | |
| `max_output_tokens` | dropped | the codex backend refuses an output cap |
| `max_tool_calls` | refused | the tool-call cap would be silently unenforced |
| `metadata` | dropped | the codex backend refuses request metadata |
| `model` | mapped | pinned to the bare model name |
| `parallel_tool_calls` | mapped | |
| `previous_response_id` | refused | the codex lane pins store: false, so the response chain the caller asked to continue would silently not continue |
| `prompt_cache_key` | mapped | |
| `prompt_cache_options` | dropped | the codex backend manages its own prompt cache |
| `prompt_cache_retention` | dropped | the codex backend manages its own prompt cache |
| `reasoning` | mapped | |
| `safety_identifier` | dropped | the codex backend refuses caller identifiers |
| `service_tier` | dropped | the codex backend has no service tiers |
| `store` | mapped | pinned off (the backend is stateless) |
| `stream` | mapped | pinned on (the backend is SSE-only) |
| `stream_options` | mapped | |
| `temperature` | dropped | the codex backend refuses sampling options |
| `text` | mapped | |
| `tool_choice` | mapped | |
| `tools` | mapped | |
| `top_logprobs` | refused | the requested log probabilities would be silently absent from the response |
| `top_p` | dropped | the codex backend refuses sampling options |
| `truncation` | dropped | the codex backend manages its own context truncation |
| `user` | dropped | the codex backend refuses caller identifiers |
| any other key | dropped | the codex backend accepts a fixed set of fields |

## reasoning\_effort budgets

Claude models take a thinking budget in tokens. On the anthropic lane and on the bedrock lane, the gateway derives that budget from your output cap:

```text theme={null}
budget = 1024 + ratio x (max_tokens - 1024)
```

| `reasoning_effort` | ratio |
| - | - |
| `minimal` | 0.025 |
| `low` | 0.15 |
| `medium` | 0.425 |
| `high` | 0.80 |
| `xhigh` | 0.92 |
| `max` | 1.0 |

`"reasoning_effort": "none"` sends no thinking budget at all.

Claude Opus and Sonnet from 4.6 on take the effort itself, through the provider's adaptive thinking. `minimal` is sent as `low`, because Anthropic accepts `low`, `medium`, `high` and `max`.

Gemini 3 and later take the effort as a native thinking level. Earlier Gemini models get a budget from the same formula, against the model's own budget range.


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