diff --git a/app/api/chat/runs/route.ts b/app/api/chat/runs/route.ts
index 0f667665b..1434a07f9 100644
--- a/app/api/chat/runs/route.ts
+++ b/app/api/chat/runs/route.ts
@@ -32,7 +32,7 @@ export async function OPTIONS() {
  * - prompt: String prompt (mutually exclusive with messages)
  * - messages: Array of UIMessages (mutually exclusive with prompt)
  * - artistId: Optional UUID of the artist account
- * - model: Optional model ID override (default anthropic/claude-haiku-4.5)
+ * - model: Optional model ID override (default moonshotai/kimi-k3)
  * - topic: Optional session title
  * - accountId: Optional accountId override (requires org API key)
  *
diff --git a/lib/agents/generalAgent/__tests__/getGeneralAgent.test.ts b/lib/agents/generalAgent/__tests__/getGeneralAgent.test.ts
index 88fbadf94..7c75797fc 100644
--- a/lib/agents/generalAgent/__tests__/getGeneralAgent.test.ts
+++ b/lib/agents/generalAgent/__tests__/getGeneralAgent.test.ts
@@ -117,7 +117,7 @@ describe("getGeneralAgent", () => {
 
       const result = await getGeneralAgent(body);
 
-      expect(result.model).toBe("openai/gpt-5.4-nano");
+      expect(result.model).toBe("moonshotai/kimi-k3");
     });
 
     it("uses custom model when specified in body", async () => {
diff --git a/lib/chat/__tests__/handleChatWorkflowStream.test.ts b/lib/chat/__tests__/handleChatWorkflowStream.test.ts
index 1af062c8b..7a37c4a77 100644
--- a/lib/chat/__tests__/handleChatWorkflowStream.test.ts
+++ b/lib/chat/__tests__/handleChatWorkflowStream.test.ts
@@ -286,7 +286,7 @@ describe("handleChatWorkflowStream", () => {
       mockStartedRun();
       await handleChatWorkflowStream(makeRequest());
       const startArgs = vi.mocked(start).mock.calls[0]?.[1]?.[0] as { modelId: string };
-      expect(startArgs.modelId).toBe("anthropic/claude-haiku-4.5");
+      expect(startArgs.modelId).toBe("moonshotai/kimi-k3");
     });
 
     // Bundle A.4 — forward the Privy JWT from the validated body into
diff --git a/lib/chat/handleChatWorkflowStream.ts b/lib/chat/handleChatWorkflowStream.ts
index 568e546bc..30b2c4086 100644
--- a/lib/chat/handleChatWorkflowStream.ts
+++ b/lib/chat/handleChatWorkflowStream.ts
@@ -1,3 +1,4 @@
+import { DEFAULT_MODEL } from "@/lib/const";
 import { NextRequest, NextResponse } from "next/server";
 import { createUIMessageStreamResponse, type UIMessageChunk } from "ai";
 import { start, getRun } from "workflow/api";
@@ -22,8 +23,6 @@ import { discoverSkills } from "@/lib/skills/discoverSkills";
 import { getSandboxSkillDirectories } from "@/lib/skills/getSandboxSkillDirectories";
 import generateUUID from "@/lib/uuid/generateUUID";
 
-const DEFAULT_MODEL_ID = "anthropic/claude-haiku-4.5";
-
 /**
  * Handles POST /api/chat/workflow.
  *
@@ -90,7 +89,7 @@ export async function handleChatWorkflowStream(request: NextRequest): Promise<Re
   await updateSession(validated.sessionId, buildActiveLifecycleUpdate(session.sandbox_state));
   void persistLatestUserMessage(validated.chatId, validated.messages as never);
 
-  const modelId = chat.model_id ?? DEFAULT_MODEL_ID;
+  const modelId = chat.model_id ?? DEFAULT_MODEL;
 
   // Connect the sandbox up-front so we can (a) read the real working
   // directory and (b) discover project-level skills. The connected
diff --git a/lib/chat/runs/__tests__/handleStartChatRun.test.ts b/lib/chat/runs/__tests__/handleStartChatRun.test.ts
index 999b12131..366690067 100644
--- a/lib/chat/runs/__tests__/handleStartChatRun.test.ts
+++ b/lib/chat/runs/__tests__/handleStartChatRun.test.ts
@@ -48,7 +48,7 @@ const validated = {
   orgId: null,
   messages: [{ id: "m1", role: "user", parts: [{ type: "text", text: "go" }] }],
   artistId: undefined,
-  modelId: "anthropic/claude-haiku-4.5",
+  modelId: "test/model-y",
 };
 
 const provisioned = {
@@ -86,7 +86,12 @@ describe("handleStartChatRun", () => {
     });
 
     expect(provisionRunSession).toHaveBeenCalledWith(
-      expect.objectContaining({ accountId: "acc-1", title: "Scheduled generation" }),
+      expect.objectContaining({
+        accountId: "acc-1",
+        title: "Scheduled generation",
+        // Provenance (chat#1956): the resolved model reaches the chat insert.
+        modelId: "test/model-y",
+      }),
     );
     // the minted key is injected as recoupAccessToken AND threaded as ephemeralKeyId
     expect(buildRunAgentInput).toHaveBeenCalledWith(
diff --git a/lib/chat/runs/__tests__/provisionRunSession.test.ts b/lib/chat/runs/__tests__/provisionRunSession.test.ts
index 3dd3a13b3..404d438f2 100644
--- a/lib/chat/runs/__tests__/provisionRunSession.test.ts
+++ b/lib/chat/runs/__tests__/provisionRunSession.test.ts
@@ -56,7 +56,7 @@ describe("provisionRunSession", () => {
   });
 
   it("installs global skills into the sandbox before discovering them", async () => {
-    await provisionRunSession({ accountId: "account-1", title: "t" });
+    await provisionRunSession({ accountId: "account-1", title: "t", modelId: "test/model-x" });
 
     // Headless runs must PROVISION skills, not just discover them (chat#1822).
     expect(installSessionGlobalSkills).toHaveBeenCalledWith({
@@ -69,10 +69,24 @@ describe("provisionRunSession", () => {
     expect(installOrder).toBeLessThan(discoverOrder);
   });
 
+  // Provenance thread-through (chat#1956): the resolved model must reach the
+  // chat insert, not stop at the workflow input.
+  it("forwards modelId to createSessionWithInitialChat", async () => {
+    await provisionRunSession({ accountId: "account-1", title: "t", modelId: "test/model-x" });
+
+    expect(createSessionWithInitialChat).toHaveBeenCalledWith(
+      expect.objectContaining({ modelId: "test/model-x" }),
+    );
+  });
+
   it("still completes the run when skill install fails (best-effort)", async () => {
     vi.mocked(installSessionGlobalSkills).mockRejectedValueOnce(new Error("install boom"));
 
-    const result = await provisionRunSession({ accountId: "account-1", title: "t" });
+    const result = await provisionRunSession({
+      accountId: "account-1",
+      title: "t",
+      modelId: "test/model-x",
+    });
 
     expect(result.session).toEqual(updated);
     expect(discoverSkills).toHaveBeenCalled();
diff --git a/lib/chat/runs/__tests__/validateChatRunRequest.test.ts b/lib/chat/runs/__tests__/validateChatRunRequest.test.ts
index aae8f0903..79c2db924 100644
--- a/lib/chat/runs/__tests__/validateChatRunRequest.test.ts
+++ b/lib/chat/runs/__tests__/validateChatRunRequest.test.ts
@@ -50,7 +50,17 @@ describe("validateChatRunRequest", () => {
 
     const noModel = await validateChatRunRequest(req({ prompt: "hi" }));
     if (noModel instanceof NextResponse) throw new Error("unexpected error");
-    expect(noModel.modelId).toBe("anthropic/claude-haiku-4.5");
+    expect(noModel.modelId).toBe("moonshotai/kimi-k3");
+
+    // cubic P2: an empty or whitespace model must normalize to the default,
+    // never persist as "" (provenance) or reach the workflow as "".
+    const emptyModel = await validateChatRunRequest(req({ prompt: "hi", model: "" }));
+    if (emptyModel instanceof NextResponse) throw new Error("unexpected error");
+    expect(emptyModel.modelId).toBe("moonshotai/kimi-k3");
+
+    const blankModel = await validateChatRunRequest(req({ prompt: "hi", model: "   " }));
+    if (blankModel instanceof NextResponse) throw new Error("unexpected error");
+    expect(blankModel.modelId).toBe("moonshotai/kimi-k3");
   });
 
   it("rejects when neither prompt nor messages is provided (400)", async () => {
diff --git a/lib/chat/runs/handleStartChatRun.ts b/lib/chat/runs/handleStartChatRun.ts
index 4122834c8..5328145c9 100644
--- a/lib/chat/runs/handleStartChatRun.ts
+++ b/lib/chat/runs/handleStartChatRun.ts
@@ -46,6 +46,7 @@ export async function handleStartChatRun(request: NextRequest): Promise<Response
       accountId,
       title: DEFAULT_RUN_SESSION_TITLE,
       artistId,
+      modelId,
     });
 
     const { rawKey, keyId } = await mintEphemeralAccountKey(accountId);
diff --git a/lib/chat/runs/provisionRunSession.ts b/lib/chat/runs/provisionRunSession.ts
index df1b054f8..34f4f1a21 100644
--- a/lib/chat/runs/provisionRunSession.ts
+++ b/lib/chat/runs/provisionRunSession.ts
@@ -37,16 +37,20 @@ export async function provisionRunSession({
   accountId,
   title,
   artistId,
+  modelId,
 }: {
   accountId: string;
   title: string;
   artistId?: string;
+  /** Resolved model for this run — written to the chat row for provenance (chat#1956). */
+  modelId: string;
 }): Promise<ProvisionedRunSession> {
   const created = await createSessionWithInitialChat({
     accountId,
     title,
     chatTitle: "Scheduled generation",
     artistId,
+    modelId,
   });
   if (created.ok === false) {
     throw new Error(
diff --git a/lib/chat/runs/validateChatRunRequest.ts b/lib/chat/runs/validateChatRunRequest.ts
index 154f47e6c..342fc14f0 100644
--- a/lib/chat/runs/validateChatRunRequest.ts
+++ b/lib/chat/runs/validateChatRunRequest.ts
@@ -6,9 +6,7 @@ import { validateAuthContext } from "@/lib/auth/validateAuthContext";
 import { errorResponse } from "@/lib/networking/errorResponse";
 import { validationErrorResponse } from "@/lib/zod/validationErrorResponse";
 import { generateUUID } from "@/lib/uuid/generateUUID";
-
-/** Default model for headless generation when the caller omits `model`. */
-export const DEFAULT_RUN_MODEL_ID = "anthropic/claude-haiku-4.5";
+import { DEFAULT_MODEL } from "@/lib/const";
 
 /**
  * Body schema for `POST /api/chat/runs` (the durable-workflow re-point,
@@ -78,11 +76,15 @@ export async function validateChatRunRequest(
     ? [{ id: generateUUID(), role: "user", parts: [{ type: "text", text: trimmedPrompt }] }]
     : (messages as UIMessage[]);
 
+  // `||` not `??`: an empty/whitespace model must fall back too, or "" would
+  // be persisted as provenance and sent to the workflow as the model id.
+  const trimmedModel = typeof model === "string" ? model.trim() : "";
+
   return {
     accountId: auth.accountId,
     orgId: auth.orgId,
     messages: uiMessages,
     artistId,
-    modelId: model ?? DEFAULT_RUN_MODEL_ID,
+    modelId: trimmedModel || DEFAULT_MODEL,
   };
 }
diff --git a/lib/const.ts b/lib/const.ts
index 86a460432..3af5c33b9 100644
--- a/lib/const.ts
+++ b/lib/const.ts
@@ -9,7 +9,14 @@ export const SMART_ACCOUNT_ADDRESS = "0xbAf31935ED514e8F7da81D0A730AB5362DEEEEb7
 export const USDC_ADDRESS = "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913" as Address;
 export const PAYMASTER_URL = `https://api.developer.coinbase.com/rpc/v1/base/${process.env.PAYMASTER_KEY}`;
 export const IMAGE_GENERATE_PRICE = "0.15";
-export const DEFAULT_MODEL = "openai/gpt-5.4-nano";
+/**
+ * THE default model, everywhere a caller picks none: interactive chats,
+ * headless runs (persisted to `chats.model_id` at provision time, chat#1956),
+ * evals, catalog batch analysis, and the general agent's fallback.
+ * kimi-k3 chosen 2026-08-12: best recall and lowest cost in a 4-model A/B on
+ * a production roster-brief task (api#830 review thread).
+ */
+export const DEFAULT_MODEL = "moonshotai/kimi-k3";
 export const LIGHTWEIGHT_MODEL = "openai/gpt-4o-mini";
 export const PRIVY_PROJECT_SECRET = process.env.PRIVY_PROJECT_SECRET;
 /** Base URL for the public API documentation site */
diff --git a/lib/sessions/__tests__/createSessionHandler.persistence.test.ts b/lib/sessions/__tests__/createSessionHandler.persistence.test.ts
index 043b65e6e..898ba58cc 100644
--- a/lib/sessions/__tests__/createSessionHandler.persistence.test.ts
+++ b/lib/sessions/__tests__/createSessionHandler.persistence.test.ts
@@ -68,6 +68,9 @@ describe("createSessionHandler — persistence", () => {
     const chatArgs = vi.mocked(insertChat).mock.calls[0][0];
     expect(chatArgs.session_id).toBe("sess_1");
     expect(chatArgs.title).toBe("New chat");
+    // Provenance (chat#1956): every writer sets model_id explicitly so the
+    // chats.model_id column default can be dropped.
+    expect(chatArgs.model_id).toBe("moonshotai/kimi-k3");
   });
 
   it("uses auth.accountId for personal sessions", async () => {
diff --git a/lib/sessions/__tests__/createSessionWithInitialChat.test.ts b/lib/sessions/__tests__/createSessionWithInitialChat.test.ts
index f30286ffd..95f9a9a75 100644
--- a/lib/sessions/__tests__/createSessionWithInitialChat.test.ts
+++ b/lib/sessions/__tests__/createSessionWithInitialChat.test.ts
@@ -16,7 +16,13 @@ vi.mock("@/lib/supabase/sessions/insertSession", () => ({ insertSession: vi.fn()
 vi.mock("@/lib/supabase/sessions/deleteSessionById", () => ({ deleteSessionById: vi.fn() }));
 vi.mock("@/lib/supabase/chats/insertChat", () => ({ insertChat: vi.fn() }));
 
-const args = { accountId: "acc-1", title: "T", chatTitle: "New chat", artistId: "art-1" };
+const args = {
+  accountId: "acc-1",
+  title: "T",
+  chatTitle: "New chat",
+  artistId: "art-1",
+  modelId: "test/model-x",
+};
 
 describe("createSessionWithInitialChat", () => {
   beforeEach(() => {
@@ -38,6 +44,13 @@ describe("createSessionWithInitialChat", () => {
     );
   });
 
+  // Provenance: the chat row must record the model that will run (chat#1956) —
+  // never rely on the chats.model_id column default to fill it in.
+  it("writes the caller's modelId onto the inserted chat row", async () => {
+    await createSessionWithInitialChat(args);
+    expect(insertChat).toHaveBeenCalledWith(expect.objectContaining({ model_id: "test/model-x" }));
+  });
+
   it("uses workspaceAccountId for the repo when provided", async () => {
     await createSessionWithInitialChat({ ...args, workspaceAccountId: "org-9" });
     expect(ensurePersonalRepo).toHaveBeenCalledWith({ accountId: "org-9" });
diff --git a/lib/sessions/chats/__tests__/createSessionChatHandler.test.ts b/lib/sessions/chats/__tests__/createSessionChatHandler.test.ts
index efc6797cd..2d91e91a4 100644
--- a/lib/sessions/chats/__tests__/createSessionChatHandler.test.ts
+++ b/lib/sessions/chats/__tests__/createSessionChatHandler.test.ts
@@ -95,6 +95,9 @@ describe("createSessionChatHandler", () => {
     expect(insertArgs.id).toBe("chat_requested");
     expect(insertArgs.session_id).toBe("sess_1");
     expect(insertArgs.title).toBe("New chat");
+    // Provenance (chat#1956): every writer sets model_id explicitly so the
+    // chats.model_id column default can be dropped.
+    expect(insertArgs.model_id).toBe("moonshotai/kimi-k3");
   });
 
   it("creates a chat with a generated id when no id is provided", async () => {
diff --git a/lib/sessions/chats/__tests__/getSessionChatsHandler.test.ts b/lib/sessions/chats/__tests__/getSessionChatsHandler.test.ts
index 624a7f75e..10a08e3da 100644
--- a/lib/sessions/chats/__tests__/getSessionChatsHandler.test.ts
+++ b/lib/sessions/chats/__tests__/getSessionChatsHandler.test.ts
@@ -70,7 +70,7 @@ describe("getSessionChatsHandler", () => {
       defaultModelId: string;
     };
     expect(body.chats).toEqual(summaries);
-    expect(body.defaultModelId).toBe("openai/gpt-5.4-nano");
+    expect(body.defaultModelId).toBe("moonshotai/kimi-k3");
     expect(getChatSummaries).toHaveBeenCalledWith({
       sessionId: "sess_1",
       accountId,
diff --git a/lib/sessions/chats/createSessionChatHandler.ts b/lib/sessions/chats/createSessionChatHandler.ts
index 868691246..433bdbc9a 100644
--- a/lib/sessions/chats/createSessionChatHandler.ts
+++ b/lib/sessions/chats/createSessionChatHandler.ts
@@ -5,6 +5,7 @@ import { validateCreateSessionChatRequest } from "@/lib/sessions/chats/validateC
 import { selectChats } from "@/lib/supabase/chats/selectChats";
 import { insertChat } from "@/lib/supabase/chats/insertChat";
 import { toChatResponse } from "@/lib/sessions/toChatResponse";
+import { DEFAULT_MODEL } from "@/lib/const";
 
 const INITIAL_CHAT_TITLE = "New chat";
 
@@ -53,6 +54,7 @@ export async function createSessionChatHandler(
     id: requestedChatId ?? generateUUID(),
     session_id: sessionId,
     title: INITIAL_CHAT_TITLE,
+    model_id: DEFAULT_MODEL,
   });
 
   if (!chatRow) {
diff --git a/lib/sessions/createSessionHandler.ts b/lib/sessions/createSessionHandler.ts
index 9667695cd..4ec02ed9f 100644
--- a/lib/sessions/createSessionHandler.ts
+++ b/lib/sessions/createSessionHandler.ts
@@ -9,6 +9,7 @@ import {
 import { failedToCreateSession } from "@/lib/sessions/failedToCreateSession";
 import { toSessionResponse } from "@/lib/sessions/toSessionResponse";
 import { toChatResponse } from "@/lib/sessions/toChatResponse";
+import { DEFAULT_MODEL } from "@/lib/const";
 
 const INITIAL_CHAT_TITLE = "New chat";
 
@@ -49,6 +50,7 @@ export async function createSessionHandler(request: NextRequest): Promise<NextRe
     title,
     chatTitle: INITIAL_CHAT_TITLE,
     artistId: body.artistId,
+    modelId: DEFAULT_MODEL,
   });
 
   if (result.ok === false) {
diff --git a/lib/sessions/createSessionWithInitialChat.ts b/lib/sessions/createSessionWithInitialChat.ts
index 766c20530..0653679fe 100644
--- a/lib/sessions/createSessionWithInitialChat.ts
+++ b/lib/sessions/createSessionWithInitialChat.ts
@@ -35,12 +35,15 @@ export async function createSessionWithInitialChat({
   title,
   chatTitle,
   artistId,
+  modelId,
 }: {
   accountId: string;
   workspaceAccountId?: string;
   title: string;
   chatTitle: string;
   artistId?: string;
+  /** Model recorded on the chat row — provenance, never left to a column default (chat#1956). */
+  modelId: string;
 }): Promise<CreateSessionWithChatResult> {
   const cloneUrl = await ensurePersonalRepo({ accountId: workspaceAccountId ?? accountId });
   if (!cloneUrl) return { ok: false, reason: "repo" };
@@ -50,7 +53,12 @@ export async function createSessionWithInitialChat({
   );
   if (!session) return { ok: false, reason: "insert" };
 
-  const chat = await insertChat({ id: generateUUID(), session_id: session.id, title: chatTitle });
+  const chat = await insertChat({
+    id: generateUUID(),
+    session_id: session.id,
+    title: chatTitle,
+    model_id: modelId,
+  });
   if (!chat) {
     const rolledBack = await deleteSessionById(session.id);
     if (!rolledBack) {