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The request block enables you to perform lightweight transformations on the payload before it gets sent to the upstream provider.

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Header Operations

You can arbitrarily set or delete HTTP headers going to the upstream server. 
request {
  set_header "x-trace-id" "trace-123";
  set_header "x-foo" concat("a-", $request.model_mapped);
  
  del_header "x-remove-me";
}
Note: If the same header is set multiple times, the last one wins. Deletions apply in order.

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Model Mapping

Use model_map to alias or hardcode model names conditionally. 
request {
  model_map "gpt-4o-mini" "gpt4o-mini-prod";
  model_map "gpt-4o-mini" $request.model;
  
  model_map_default $request.model;
}
  • Maps $request.model to $request.model_mapped.
  • Exact match on the from string.
  • If no matches occur, model_map_default dictates what $request.model_mapped becomes.

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JSON Mutations

Apply lightweight mutations directly to the upstream JSON body. 
request {
  json_set "$.stream" true;
  json_set_if_absent "$.instructions" "";
  
  json_rename "$.max_tokens" "$.max_completion_tokens";
  json_wrap_input_text "$.input";
  json_del "$.tools";
}
  • Supports a subset of object-path JSONPath expressions (e.g. $.a.b.c).
  • json_set values support primitives (true, false, null, integers, strings) or expressions (like concat(...)).
  • json_wrap_input_text converts a string field into an OpenAI Responses input message list, leaves missing or already-array values unchanged, and rejects other types.

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Structural Request Mapping

Use req_map to apply heavy, cross-provider schema transformations (such as converting an OpenAI JSON request into a Gemini or Anthropic JSON request). 
request { req_map <mode>; }
Use after_req_map when a request JSON mutation must run after the structural mapping step. 
request {
  req_map openai_chat_to_anthropic_messages;

  after_req_map {
    json_set "$.anthropic_version" "bedrock-2023-05-31";
    json_del_if_missing "$.tool_choice" "$.tools";
  }
}
  • Only request JSON mutation directives are allowed inside after_req_map.
  • If no req_map is configured, after_req_map runs after the normal request JSON operations.

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Built-in Modes (v0.1)

  • openai_chat_to_openai_responses
  • anthropic_to_openai_chat
  • gemini_to_openai_chat
  • openai_chat_to_gemini_generate_content
  • openai_chat_to_anthropic_messages