Dynamic Parameters

Not yet available. The Agent SDK is tracked to be built — today, use the Client SDKs against the live chat completions API. The docs below describe the intended design.

Static parameters — a fixed temperature, a single model slug — work for most loops. Dynamic parameters let you compute them fresh each turn based on the current item list, so the agent can adapt as it runs.

The dynamicParams function#

Pass a function to callModel() under dynamicParams. The SDK calls it with the current item list immediately before each turn and merges the returned values into the call parameters.

const result = await client.callModel({
  model: "anthropic/claude-sonnet-5",
  messages: initialMessages,
  tools: myTools,
  dynamicParams: (items) => {
    const turnCount = new Set(items.map((i) => i.turnIndex)).size;

    // Cool off temperature as the agent progresses
    return {
      temperature: Math.max(0.2, 1.0 - turnCount * 0.1),
    };
  },
});

Switching models mid-loop#

Return a new model slug from dynamicParams to route different turns to different models — for example, use a cheaper model for tool-heavy exploration turns and a more capable one for final synthesis.

dynamicParams: (items) => {
  const lastItem = items[items.length - 1];
  const isFinalising = lastItem?.type === "message" && lastItem.role === "user"
    && lastItem.content.includes("summarise");

  return {
    model: isFinalising ? "anthropic/claude-opus-4.8" : "meta-llama/llama-4-maverick",
  };
},

Adjusting tool availability#

Return a different tools array to expose or hide tools as the loop progresses — restricting tools when the agent should focus on outputting a result rather than making more calls.

dynamicParams: (items) => {
  const toolCalls = items.filter((i) => i.type === "tool_call").length;
  return {
    tools: toolCalls >= 5 ? [] : allTools,  // No more tools after 5 calls
  };
},

What you can return#

The function may return any subset of CallModelParams. These fields are merged on top of the static parameters you passed to callModel():

• model
• tools
• temperature
• topP
• maxTokens
• stream
• stopConditions

You cannot change messages or inputItems via dynamicParams — those are set once per callModel() call.

Interaction with stop conditions#

Dynamic stop conditions (returned from dynamicParams) are merged with any static stop conditions you declared. The loop stops as soon as any condition is met.

Also see#

• Call Model — the callModel() API.
• Stop Conditions — declarative loop termination.
• Next Turn Params — passing context forward without affecting the item list.
• API Reference — full type definitions.