Request field map

Rust and the proxy express the same request semantics through different envelopes. Rust uses an OpenAI-shaped serde_json::Value; the proxy groups its portable subset under config and everything else under provider_config.

Availability: Rust: flexible top-level JSON · Proxy/clients: typed compact envelope

Rust engine request

These are the stable, adapter-recognized fields. A field marked “mapped” is renamed or reshaped for the selected provider; unsupported controls are omitted.

There is no x-xai namespace. OpenAI additionally recognizes store, prompt_cache_key, prompt_cache_retention, safety_identifier, and speed. Anthropic recognizes cache_control, thinking, output_config, and speed. Those fields are provider-specific even when they are not wrapped in an x-* namespace.

The request is a Value, so Rust does not reject unknown keys up front. Adapters deliberately select only fields they understand. Do not assume an arbitrary top-level key reaches the provider; use a documented native namespace.

Reasoning values and family-specific clamps are canonicalized in Reasoning controls. Native namespaces and precedence are covered in Native provider controls.

Message fields

Content blocks may use OpenAI image_url, Anthropic image, or Gemini inline_data input forms. See Images and vision.

Lossless reasoning round-trip

Preserve the complete assistant message, including reasoning[] and tool-call signature objects. llmshim reconstructs native reasoning only when the stored origin matches the target family and wire; encrypted data also requires a matching issuer binding. Anthropic thinking remains first and ordered, and Responses items retain their encrypted payloads. Unknown origins/families are never replayed. See reasoning replay.

Proxy request

The exact config children are:

For example, this proxy fragment:

{
  "config": {"reasoning_effort": "high"},
  "provider_config": {
    "tools": [],
    "x-anthropic": {"disable_1m_context": true}
  }
}

becomes engine fields named reasoning_effort, tools, and x-anthropic. Because provider_config is merged after config, a same-named child there overrides the portable value. Prefer the x-* namespace for an intentional native override; it makes that loss of portability visible.

model and messages are reserved at the provider_config root. After named route defaults and aliases are resolved, the proxy validates only the selected provider's active namespace and wire. Every resolvable explicit fallback is validated the same way before the primary request runs. The proxy rejects fields that would replace the admitted model or main history/input container: x-openai.model/input, x-chatgpt.input, x-anthropic.model/messages, x-gemini.contents, x-openrouter.model/messages, and the corresponding model plus messages/input fields for any OpenAiCompatible provider's configured namespace and wire. A namespace is inactive only when neither the primary nor an explicit fallback or route can select its provider. Native system and instructions, tool definitions, schemas, output limits, OpenRouter routing preferences, and other documented controls remain valid and are included in the estimate when active.

Output contracts

response_format: {type:"json_schema", json_schema:{name?, schema, strict?}} requests validated JSON output. x-shim controls structured_output (auto|native|forced_tool|prompt), tool_calling (auto|native|prompt), and reasoning_capture (off|forced_tool). See capability shims for path selection, bounded repair, streaming behavior, and provenance.