From 1fc96025d66167d87230e678852d658c3683fda2 Mon Sep 17 00:00:00 2001
From: wintrover <wintrover@users.noreply.github.com>
Date: Sat, 13 Jun 2026 14:33:28 +0900
Subject: [PATCH] feat: allow configuring a separate model for subagents

Add [subagents] config section to config.toml that allows overriding
the model used by subagents independently from the parent agent.

Priority order:
1. KIMI_SUBAGENT_MODEL env var (highest)
2. [subagents].model in config.toml
3. Parent agent model (default fallback)

Closes #568
---
 packages/agent-core/src/config/schema.ts      |  8 +++++++
 .../agent-core/src/session/subagent-host.ts   | 22 ++++++++++++++-----
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/packages/agent-core/src/config/schema.ts b/packages/agent-core/src/config/schema.ts
index 094239b73..e00d11328 100644
--- a/packages/agent-core/src/config/schema.ts
+++ b/packages/agent-core/src/config/schema.ts
@@ -104,6 +104,12 @@ export const BackgroundConfigSchema = z.object({
 
 export type BackgroundConfig = z.infer<typeof BackgroundConfigSchema>;
 
+export const SubagentConfigSchema = z.object({
+  model: z.string().optional(),
+});
+
+export type SubagentConfig = z.infer<typeof SubagentConfigSchema>;
+
 export const ExperimentalConfigSchema = z.record(z.string(), z.boolean());
 
 export type ExperimentalConfig = z.infer<typeof ExperimentalConfigSchema>;
@@ -204,6 +210,7 @@ export const KimiConfigSchema = z.object({
   loopControl: LoopControlSchema.optional(),
   background: BackgroundConfigSchema.optional(),
   experimental: ExperimentalConfigSchema.optional(),
+  subagents: SubagentConfigSchema.optional(),
   telemetry: z.boolean().optional(),
   raw: z.record(z.string(), z.unknown()).optional(),
 });
@@ -243,6 +250,7 @@ export const KimiConfigPatchSchema = z
     loopControl: LoopControlPatchSchema.optional(),
     background: BackgroundConfigPatchSchema.optional(),
     experimental: ExperimentalConfigPatchSchema.optional(),
+    subagents: SubagentConfigSchema.optional(),
     telemetry: z.boolean().optional(),
   })
   .strict();
diff --git a/packages/agent-core/src/session/subagent-host.ts b/packages/agent-core/src/session/subagent-host.ts
index b47e1cd68..f6ee96c60 100644
--- a/packages/agent-core/src/session/subagent-host.ts
+++ b/packages/agent-core/src/session/subagent-host.ts
@@ -143,7 +143,7 @@ export class SessionSubagentHost {
     const completion = this.runWithActiveChild(agentId, options, async (runOptions) => {
       this.emitSubagentSpawned(parent, agentId, profileName, runOptions);
       try {
-        child.config.update({ modelAlias: parent.config.modelAlias });
+        child.config.update({ modelAlias: this.resolveSubagentModel(parent) });
         return await this.runPromptTurn(parent, agentId, child, profileName, runOptions);
       } catch (error) {
         this.emitSubagentFailed(parent, agentId, runOptions, error);
@@ -159,7 +159,7 @@ export class SessionSubagentHost {
     const completion = this.runWithActiveChild(agentId, options, async (runOptions) => {
       try {
         runOptions.signal.throwIfAborted();
-        child.config.update({ modelAlias: parent.config.modelAlias });
+        child.config.update({ modelAlias: this.resolveSubagentModel(parent) });
         this.emitSubagentStarted(parent, agentId);
         const turnId = child.turn.retry('agent-host');
         if (turnId === null) {
@@ -220,7 +220,7 @@ export class SessionSubagentHost {
     );
 
     child.config.update({
-      modelAlias: parent.config.modelAlias,
+      modelAlias: this.resolveSubagentModel(parent),
       thinkingLevel: parent.config.thinkingLevel,
       systemPrompt: parent.config.systemPrompt,
     });
@@ -350,15 +350,27 @@ export class SessionSubagentHost {
     return { result, usage };
   }
 
+  private resolveSubagentModel(parent: Agent): string {
+    // Env var override has highest priority
+    const envModel = process.env.KIMI_SUBAGENT_MODEL;
+    if (envModel) return envModel;
+
+    // Config override from [subagents] section
+    const subagentModel = this.session.options.config?.subagents?.model;
+    if (subagentModel) return subagentModel;
+
+    // Default: inherit parent model
+    return parent.config.modelAlias;
+  }
+
   private async configureChild(
     parent: Agent,
     child: Agent,
     profile: ResolvedAgentProfile,
   ): Promise<void> {
-    // A subagent always inherits the parent agent's model.
     child.config.update({
       cwd: parent.config.cwd,
-      modelAlias: parent.config.modelAlias,
+      modelAlias: this.resolveSubagentModel(parent),
       thinkingLevel: parent.config.thinkingLevel,
     });