Struct ChatParams 

pub struct ChatParams {
    pub messages: Vec<ChatMessage>,
    pub tools: Option<Vec<ToolDefinition>>,
    pub tool_choice: Option<ToolChoice>,
    pub temperature: Option<f32>,
    pub max_tokens: Option<u32>,
    pub system: Option<String>,
    pub reasoning_budget: Option<u32>,
    pub structured_output: Option<JsonSchema>,
    pub timeout: Option<Duration>,
    pub extra_headers: Option<HeaderMap>,
    pub metadata: HashMap<String, Value>,
}

Parameters for a chat completion request.

Most fields are optional — at minimum you need messages. Use struct-update syntax for concise construction:

use llm_stack::{ChatParams, ChatMessage};

let params = ChatParams {
    messages: vec![ChatMessage::user("Hello")],
    max_tokens: Some(256),
    temperature: Some(0.7),
    ..Default::default()
};

Serialization

ChatParams implements Serialize / Deserialize for logging and request replay. The timeout and extra_headers fields are skipped during serialization because they are transport-layer concerns, not part of the logical request.

Equality

PartialEq is structural. The extra_headers field uses http::HeaderMap, whose equality comparison is order-sensitive for multi-valued headers. In practice this only matters in tests via MockProvider::recorded_calls.

Fields

messages: Vec<ChatMessage>

The conversation history.

tools: Option<Vec<ToolDefinition>>

Tool definitions the model may invoke.

tool_choice: Option<ToolChoice>

Controls whether and how the model uses tools.

temperature: Option<f32>

Sampling temperature (0.0 = deterministic, higher = more random).

max_tokens: Option<u32>

Upper bound on generated tokens.

system: Option<String>

System prompt (used by providers that accept it separately from the message list).

reasoning_budget: Option<u32>

Token budget for chain-of-thought reasoning, if the provider supports Capability::Reasoning.

structured_output: Option<JsonSchema>

JSON Schema that the model’s output must conform to.

timeout: Option<Duration>

Per-request timeout. Skipped during serialization.

extra_headers: Option<HeaderMap>

Extra HTTP headers to send with this request. Skipped during serialization.

metadata: HashMap<String, Value>

Arbitrary key-value pairs forwarded to the provider. Useful for provider-specific features that don’t have a dedicated field.

Trait Implementations

impl Clone for ChatParams

fn clone(&self) -> ChatParams

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ChatParams

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for ChatParams

fn default() -> ChatParams

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for ChatParams

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Loggable for ChatParams

fn log_description(&self) -> String

Return a description of the operation for logging.

impl PartialEq for ChatParams

fn eq(&self, other: &ChatParams) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for ChatParams

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for ChatParams