diff --git a/docs/src/content/docs/reference/scripts/chat-participants.mdx b/docs/src/content/docs/reference/scripts/chat-participants.mdx
new file mode 100644
index 0000000000..cd63298df0
--- /dev/null
+++ b/docs/src/content/docs/reference/scripts/chat-participants.mdx
@@ -0,0 +1,47 @@
+---
+title: Chat Participants
+sidebar:
+    order: 50
+---
+import { Code } from '@astrojs/starlight/components';
+import scriptSource from "../../../../../../packages/sample/genaisrc/multi-turn.genai.js?raw"
+
+
+The `defChatParticipant` allows to register a function that can add new user messages in the chat sequence.
+This allows to create multi-turn chat, or to simulate a conversation with multiple participants.
+
+```js
+let turn = 0
+defChatParticipant((_, messages) => {
+    if (++turn === 1) _.$`Are you sure?`
+})
+```
+
+In the example above, the `defChatParticipant` function is used to register a function that will be called every time a new message is added to the chat.
+
+The function receives two arguments: the first argument is the `Chat` object, and the second argument is the list of messages that have been added to the chat since the last call to the function.
+
+```js
+defChatParticipant(async (_, messages) => {
+  const text = messages.at(-1).content
+  ...
+})
+```
+
+## Tracking turns
+
+The participant will be called on every turn so it is important to keep track of the turns to avoid infinite loops.
+
+```js
+let turn = 0
+defChatParticipant((_, messages) => {
+    if (++turn === 1) _.$`Are you sure?`
+})
+```
+
+
+## Example: QA generator
+
+This script uses a multi-turn chat to generate questions, answers and validate the quality of the answers.
+
+<Code code={scriptSource} wrap={true} lang="js" title="qa-gen.genai.js" />
diff --git a/packages/core/src/chat.ts b/packages/core/src/chat.ts
index b7c59d8adb..8f03dc6a2d 100644
--- a/packages/core/src/chat.ts
+++ b/packages/core/src/chat.ts
@@ -402,7 +402,6 @@ async function processChatMessage(
     functions: ChatFunctionCallback[],
     chatParticipants: ChatParticipant[],
     schemas: Record<string, JSONSchema>,
-    vars: Partial<ExpansionVariables>,
     genVars: Record<string, string>,
     options: GenerationOptions
 ): Promise<RunPromptResult> {
@@ -445,11 +444,7 @@ async function processChatMessage(
                 const { label } = participantOptions || {}
                 trace.startDetails(`🙋 participant ${label || ""}`)
 
-                const ctx = createChatTurnGenerationContext(
-                    options,
-                    vars,
-                    trace
-                )
+                const ctx = createChatTurnGenerationContext(options, trace)
                 await generator(ctx, structuredClone(messages))
                 const node = ctx.node
                 checkCancelled(cancellationToken)
@@ -578,7 +573,6 @@ export async function executeChatSession(
                     functions,
                     chatParticipants,
                     schemas,
-                    vars,
                     genVars,
                     genOptions
                 )
diff --git a/packages/core/src/promptcontext.ts b/packages/core/src/promptcontext.ts
index 1f46355247..8f33130ab7 100644
--- a/packages/core/src/promptcontext.ts
+++ b/packages/core/src/promptcontext.ts
@@ -198,7 +198,7 @@ export function createPromptContext(
     }
 
     const ctx = Object.freeze<PromptContext & RunPromptContextNode>({
-        ...createChatGenerationContext(options, env, trace),
+        ...createChatGenerationContext(options, trace),
         script: () => {},
         system: () => {},
         env,
@@ -227,7 +227,7 @@ export function createPromptContext(
                 infoCb?.({ text: `run prompt ${label || ""}` })
 
                 const genOptions = mergeGenerationOptions(options, runOptions)
-                const ctx = createChatGenerationContext(genOptions, vars, trace)
+                const ctx = createChatGenerationContext(genOptions, trace)
                 if (typeof generator === "string")
                     ctx.node.children.push(createTextNode(generator))
                 else await generator(ctx)
diff --git a/packages/core/src/runpromptcontext.ts b/packages/core/src/runpromptcontext.ts
index 2842031862..469cae28f3 100644
--- a/packages/core/src/runpromptcontext.ts
+++ b/packages/core/src/runpromptcontext.ts
@@ -22,10 +22,8 @@ import { resolveFileDataUri } from "./file"
 
 export function createChatTurnGenerationContext(
     options: GenerationOptions,
-    vars: Partial<ExpansionVariables>,
     trace: MarkdownTrace
 ): ChatTurnGenerationContext & { node: PromptNode } {
-    const { cancellationToken, infoCb } = options || {}
     const node: PromptNode = { children: [] }
 
     const log = (...args: any[]) => {
@@ -115,10 +113,9 @@ export interface RunPromptContextNode extends ChatGenerationContext {
 
 export function createChatGenerationContext(
     options: GenerationOptions,
-    vars: Partial<ExpansionVariables>,
     trace: MarkdownTrace
 ): RunPromptContextNode {
-    const turnCtx = createChatTurnGenerationContext(options, vars, trace)
+    const turnCtx = createChatTurnGenerationContext(options, trace)
     const node = turnCtx.node
 
     const defTool: (
diff --git a/packages/sample/genaisrc/multi-turn.genai.js b/packages/sample/genaisrc/multi-turn.genai.js
index 74bae0a09d..1b826081f2 100644
--- a/packages/sample/genaisrc/multi-turn.genai.js
+++ b/packages/sample/genaisrc/multi-turn.genai.js
@@ -3,10 +3,9 @@ script({
     title: "Multi-turn conversation",
     files: ["src/rag/markdown.md"],
     system: ["system", "system.files"],
+    tests: {},
 })
 
-def("FILE", env.files)
-
 let turn = 0
 defChatParticipant(
     async (_, messages) => {
@@ -79,4 +78,5 @@ Answer the QUESTION using the contents in FILE.
     { label: "answerer" }
 )
 
+def("FILE", env.files)
 $`Generate a set of questions for the files to build a FAQ. Format one line per question in text.`