diff --git a/src/commands/issue/plan.ts b/src/commands/issue/plan.ts
index 7ce8959f6..f5595fed0 100644
--- a/src/commands/issue/plan.ts
+++ b/src/commands/issue/plan.ts
@@ -26,6 +26,7 @@ import {
   extractNoSolutionReason,
   extractRootCauses,
   extractSolution,
+  requireAutofixRunId,
   type SolutionArtifact,
 } from "../../types/seer.js";
 import {
@@ -54,7 +55,7 @@ type NoSolutionContext = {
 
 /** Return type for issue plan — includes state metadata and solution data */
 type PlanData = {
-  run_id: number;
+  run_id: string | number;
   status: string;
   /** The solution data (without the artifact wrapper). Null when no solution is available. */
   solution: SolutionArtifact["data"] | null;
@@ -141,7 +142,7 @@ function buildNoSolutionContext(
 function buildPlanData(state: AutofixState): PlanData {
   const solution = extractSolution(state);
   const data: PlanData = {
-    run_id: state.run_id,
+    run_id: requireAutofixRunId(state),
     status: state.status,
     solution: solution?.data ?? null,
   };
@@ -235,7 +236,7 @@ export const planCommand = buildCommand({
         }
       }
 
-      await triggerSolutionPlanning(org, numericId, state.run_id);
+      await triggerSolutionPlanning(org, numericId, requireAutofixRunId(state));
 
       // Poll until solution is ready or terminal
       const finalState = await pollAutofixState({
diff --git a/src/lib/api/seer.ts b/src/lib/api/seer.ts
index d0437f473..505ad6a4a 100644
--- a/src/lib/api/seer.ts
+++ b/src/lib/api/seer.ts
@@ -54,27 +54,26 @@ function normalizeAgentStatus(status: string): string {
  *
  * @param orgSlug - The organization slug
  * @param issueId - The numeric Sentry issue ID
- * @returns The trigger response with run_id
+ * @returns The trigger response with `sentry_run_id` and the legacy `run_id`
  * @throws {ApiError} On API errors (402 = no budget, 403 = not enabled)
  */
 export async function triggerRootCauseAnalysis(
   orgSlug: string,
   issueId: string
-): Promise<{ run_id: number }> {
+): Promise<{ run_id?: number; sentry_run_id: string | null }> {
   const regionUrl = await resolveOrgRegion(orgSlug);
 
-  const { data } = await apiRequestToRegion<{ run_id: number }>(
-    regionUrl,
-    `/organizations/${orgSlug}/issues/${issueId}/autofix/`,
-    {
-      method: "POST",
-      params: EXPLORER_MODE_PARAMS,
-      body: {
-        step: "root_cause",
-        referrer: "api.cli",
-      },
-    }
-  );
+  const { data } = await apiRequestToRegion<{
+    run_id?: number;
+    sentry_run_id: string | null;
+  }>(regionUrl, `/organizations/${orgSlug}/issues/${issueId}/autofix/`, {
+    method: "POST",
+    params: EXPLORER_MODE_PARAMS,
+    body: {
+      step: "root_cause",
+      referrer: "api.cli",
+    },
+  });
   return data;
 }
 
@@ -113,21 +112,24 @@ export async function getAutofixState(
  * Trigger solution planning for an existing autofix run.
  *
  * Posts to the agent-based autofix endpoint with `step: "solution"` and
- * the existing `run_id`. The agent continues from root cause analysis
- * to generating a solution plan.
+ * the existing run ID (from {@link requireAutofixRunId}).
  *
  * @param orgSlug - The organization slug
  * @param issueId - The numeric Sentry issue ID
- * @param runId - The autofix run ID
+ * @param runId - The autofix run ID (see {@link requireAutofixRunId})
  * @returns The response from the API
  */
 export async function triggerSolutionPlanning(
   orgSlug: string,
   issueId: string,
-  runId: number
+  runId: string | number
 ): Promise<unknown> {
   const regionUrl = await resolveOrgRegion(orgSlug);
 
+  // A UUID sent under run_id (an IntegerField) fails server-side validation.
+  const runIdBodyField =
+    typeof runId === "string" ? { sentry_run_id: runId } : { run_id: runId };
+
   const { data } = await apiRequestToRegion(
     regionUrl,
     `/organizations/${orgSlug}/issues/${issueId}/autofix/`,
@@ -136,7 +138,7 @@ export async function triggerSolutionPlanning(
       params: EXPLORER_MODE_PARAMS,
       body: {
         step: "solution",
-        run_id: runId,
+        ...runIdBodyField,
         referrer: "api.cli",
       },
     }
diff --git a/src/types/seer.ts b/src/types/seer.ts
index d7803714d..f83e6ca41 100644
--- a/src/types/seer.ts
+++ b/src/types/seer.ts
@@ -172,7 +172,10 @@ export type SolutionArtifact = z.infer<typeof SolutionArtifactSchema>;
 
 export const AutofixStateSchema = z
   .object({
-    run_id: z.number(),
+    /** @deprecated Use sentry_run_id instead. */
+    run_id: z.number().optional(),
+    /** Null for legacy runs predating this field. */
+    sentry_run_id: z.string().nullable().optional(),
     status: z.string(),
     updated_at: z.string().optional(),
     request: z
@@ -242,6 +245,18 @@ export function isTerminalStatus(status: string): boolean {
   return TERMINAL_STATUSES.includes(status as AutofixStatus);
 }
 
+// At least one of sentry_run_id/run_id is always present on a non-null
+// autofix state, so a missing run ID means a malformed response.
+export function requireAutofixRunId(state: AutofixState): string | number {
+  const runId = state.sentry_run_id ?? state.run_id;
+  if (runId === undefined) {
+    throw new Error(
+      "Unexpected autofix response: missing both sentry_run_id and run_id."
+    );
+  }
+  return runId;
+}
+
 /** Container that may hold root cause analysis data (legacy format) */
 type WithCauses = { key: string; causes?: RootCause[] };
 
diff --git a/test/lib/api-client.seer.test.ts b/test/lib/api-client.seer.test.ts
index afcbcfe3f..ba5ade22b 100644
--- a/test/lib/api-client.seer.test.ts
+++ b/test/lib/api-client.seer.test.ts
@@ -110,7 +110,7 @@ describe("getAutofixState", () => {
       return new Response(
         JSON.stringify({
           autofix: {
-            run_id: 12_345,
+            sentry_run_id: "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
             status: "processing",
             blocks: [],
             updated_at: "2025-01-01T00:00:00Z",
@@ -125,7 +125,7 @@ describe("getAutofixState", () => {
 
     const result = await getAutofixState("test-org", "123456789");
 
-    expect(result?.run_id).toBe(12_345);
+    expect(result?.sentry_run_id).toBe("a1b2c3d4-e5f6-7890-abcd-ef1234567890");
     expect(result?.status).toBe("PROCESSING");
     expect(capturedRequest?.method).toBe("GET");
     expect(capturedRequest?.url).toContain(
@@ -134,6 +134,29 @@ describe("getAutofixState", () => {
     expect(capturedRequest?.url).toContain("mode=explorer");
   });
 
+  test("still parses legacy run_id when sentry_run_id is absent", async () => {
+    globalThis.fetch = async () =>
+      new Response(
+        JSON.stringify({
+          autofix: {
+            run_id: 12_345,
+            status: "processing",
+            blocks: [],
+            updated_at: "2025-01-01T00:00:00Z",
+          },
+        }),
+        {
+          status: 200,
+          headers: { "Content-Type": "application/json" },
+        }
+      );
+
+    const result = await getAutofixState("test-org", "123456789");
+
+    expect(result?.run_id).toBe(12_345);
+    expect(result?.sentry_run_id).toBeUndefined();
+  });
+
   test("normalizes agent status values to uppercase", async () => {
     globalThis.fetch = async () =>
       new Response(
@@ -274,4 +297,37 @@ describe("triggerSolutionPlanning", () => {
       referrer: "api.cli",
     });
   });
+
+  test("sends a UUID run ID under the sentry_run_id body field, not run_id", async () => {
+    let capturedBody: unknown;
+
+    globalThis.fetch = async (input: RequestInfo | URL, init?: RequestInit) => {
+      capturedBody = await new Request(input, init).json();
+
+      return new Response(
+        JSON.stringify({
+          run_id: 12_345,
+          sentry_run_id: "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+        }),
+        {
+          status: 202,
+          headers: { "Content-Type": "application/json" },
+        }
+      );
+    };
+
+    await triggerSolutionPlanning(
+      "test-org",
+      "123456789",
+      "a1b2c3d4-e5f6-7890-abcd-ef1234567890"
+    );
+
+    // sentry_run_id is a UUIDField server-side; run_id is an IntegerField.
+    // Sending the UUID under run_id would fail server-side validation.
+    expect(capturedBody).toEqual({
+      step: "solution",
+      sentry_run_id: "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+      referrer: "api.cli",
+    });
+  });
 });
diff --git a/test/types/seer.test.ts b/test/types/seer.test.ts
index f202b4145..96db67ec8 100644
--- a/test/types/seer.test.ts
+++ b/test/types/seer.test.ts
@@ -13,6 +13,7 @@ import {
   extractSolution,
   isTerminalStatus,
   type RootCause,
+  requireAutofixRunId,
   TERMINAL_STATUSES,
 } from "../../src/types/seer.js";
 
@@ -49,6 +50,29 @@ describe("isTerminalStatus", () => {
   });
 });
 
+describe("requireAutofixRunId", () => {
+  test("prefers sentry_run_id over legacy run_id", () => {
+    const state: AutofixState = {
+      sentry_run_id: "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+      run_id: 123,
+      status: "COMPLETED",
+    };
+    expect(requireAutofixRunId(state)).toBe(
+      "a1b2c3d4-e5f6-7890-abcd-ef1234567890"
+    );
+  });
+
+  test("falls back to legacy run_id when sentry_run_id is absent", () => {
+    const state: AutofixState = { run_id: 123, status: "COMPLETED" };
+    expect(requireAutofixRunId(state)).toBe(123);
+  });
+
+  test("throws when neither field is present", () => {
+    const state: AutofixState = { status: "COMPLETED" };
+    expect(() => requireAutofixRunId(state)).toThrow(/missing both/);
+  });
+});
+
 describe("extractRootCauses", () => {
   test("extracts causes from root_cause_analysis step", () => {
     const state: AutofixState = {