diff --git a/src/app/.well-known/agent-card.json/route.ts b/src/app/.well-known/agent-card.json/route.ts
new file mode 100644
index 000000000000..031c4081c6d2
--- /dev/null
+++ b/src/app/.well-known/agent-card.json/route.ts
@@ -0,0 +1,118 @@
+/**
+ * Agent Card Endpoint — /.well-known/agent-card.json
+ *
+ * Serves the OmniRoute A2A Agent Card in the A2A Protocol v1.0 shape for
+ * discovery by 1.0 clients (a2a-sdk 1.x, Hermes, …). The legacy v0.3 card
+ * remains available at /.well-known/agent.json.
+ *
+ * `supportedInterfaces` declares both protocol versions against the same
+ * JSON-RPC endpoint — the v1.0 route handler accepts both `SendMessage` and
+ * the legacy `message/send` (see src/app/a2a/route.ts).
+ */
+
+import { NextResponse } from "next/server";
+
+import { getFleetSkills } from "@/lib/conductor/fleetSkills";
+
+const PACKAGE_VERSION = process.env.npm_package_version || "1.8.1";
+const BASE_URL = process.env.OMNIROUTE_BASE_URL || "http://localhost:20128";
+
+/**
+ * GET /.well-known/agent-card.json
+ *
+ * Returns the OmniRoute Agent Card (A2A v1.0).
+ */
+export async function GET() {
+  const fleetSkills = await getFleetSkills();
+
+  const agentCard = {
+    name: "OmniRoute AI Gateway",
+    description:
+      "Intelligent AI routing gateway with 36+ providers, smart fallback, quota tracking, " +
+      "format translation, and auto-managed combos. Routes AI requests to the optimal " +
+      "provider based on cost, latency, quota availability, and task requirements.",
+    url: `${BASE_URL}/a2a`,
+    version: PACKAGE_VERSION,
+    supportedInterfaces: [
+      {
+        url: `${BASE_URL}/a2a`,
+        protocolBinding: "JSONRPC",
+        protocolVersion: "1.0",
+      },
+      {
+        url: `${BASE_URL}/a2a`,
+        protocolBinding: "JSONRPC",
+        protocolVersion: "0.3",
+      },
+    ],
+    defaultInputModes: ["text/plain"],
+    defaultOutputModes: ["text/plain"],
+    capabilities: {
+      streaming: true,
+      pushNotifications: false,
+    },
+    skills: [
+      {
+        id: "smart-routing",
+        name: "Smart Request Routing",
+        description:
+          "Routes AI requests to the optimal provider based on quota, cost, latency, and reliability.",
+        tags: ["routing", "llm", "optimization", "fallback"],
+        examples: [
+          "Route this coding task to the fastest available model",
+          "Send this review to an analytical model under a $0.50 budget",
+        ],
+      },
+      {
+        id: "quota-management",
+        name: "Quota & Cost Management",
+        description:
+          "Tracks and manages API quotas across providers with auto-fallback when quotas are exhausted.",
+        tags: ["quota", "cost", "monitoring", "budget"],
+        examples: ["Check remaining quota for all providers", "Generate a cost report for today"],
+      },
+      {
+        id: "provider-discovery",
+        name: "Provider Discovery",
+        description:
+          "Discovers providers that can handle a requested capability (chat, images, audio, search, embeddings, rerank, video).",
+        tags: ["providers", "discovery", "capabilities", "health"],
+        examples: ["Which providers can handle image generation?", "Find healthy providers for embeddings"],
+      },
+      {
+        id: "cost-analysis",
+        name: "Cost Analysis",
+        description: "Analyzes usage costs by provider and model and returns cost-saving opportunities.",
+        tags: ["cost", "usage", "analytics", "optimization"],
+        examples: ["How much did we spend this week?", "Which provider costs the most?"],
+      },
+      {
+        id: "health-report",
+        name: "Health Report",
+        description:
+          "Summarizes provider health, circuit-breaker state, rate-limit queues, and telemetry into a structured report.",
+        tags: ["health", "monitoring", "resilience", "telemetry"],
+        examples: ["Is everything healthy?", "Report degraded providers and retry timing"],
+      },
+      {
+        id: "list-capabilities",
+        name: "List Capabilities",
+        description: "Returns the full catalog of OmniRoute agent skills.",
+        tags: ["discovery", "capabilities"],
+        examples: ["What can you do?", "List your skills"],
+      },
+      ...fleetSkills,
+    ],
+    security: {
+      schemes: ["api-key"],
+      apiKeyHeader: "Authorization",
+    },
+  };
+
+  return NextResponse.json(agentCard, {
+    headers: {
+      "Cache-Control": "public, max-age=3600",
+      "Content-Type": "application/json",
+    },
+  });
+}
diff --git a/src/app/a2a/route.ts b/src/app/a2a/route.ts
index 7a5d4ec37b53..e9e90a99abbc 100644
--- a/src/app/a2a/route.ts
+++ b/src/app/a2a/route.ts
@@ -18,6 +18,63 @@ import { createA2AStream, SSE_HEADERS } from "@/lib/a2a/streaming";
 import { A2A_SKILL_HANDLERS, executeA2ATaskWithState } from "@/lib/a2a/taskExecution";
 import { getSettings } from "@/lib/db/settings";
 
+// ============ A2A v1.0 ↔ v0.3 compatibility layer ============
+// A2A 1.0 renamed the JSON-RPC methods (message/send → SendMessage,
+// message/stream → SendStreamingMessage) and changed the synchronous
+// response shape: a 1.0 client reads the reply from
+// `task.status.message.parts[].text` (and `task.artifacts`), whereas OmniRoute's
+// v0.3 server returns top-level `artifacts`/`metadata`. This layer aliases the
+// 1.0 method names and reshapes the synchronous response so 1.0 clients
+// (a2a-sdk 1.x, Hermes, …) can call the endpoint unchanged. v0.3 clients are
+// unaffected.
+
+const V1_METHOD_ALIASES: Record<string, string> = {
+  SendMessage: "message/send",
+  SendStreamingMessage: "message/stream",
+};
+
+/** Map a v0.3 task state to the v1.0 TASK_STATE_* enum string. */
+function toV1State(state: string): string {
+  const s = state.toUpperCase();
+  return s.startsWith("TASK_STATE_") ? s : `TASK_STATE_${s}`;
+}
+
+/**
+ * Rebuild a v1.0 Task from a v0.3 task + skill result. v0.3 carries the reply in
+ * `artifacts[].content` (type: "text"); v1.0 expects the text inside
+ * `task.status.message.parts[].text` and `task.artifacts` as Message parts.
+ */
+function buildV1Task(
+  task: { id: string; state: string },
+  result: { artifacts?: unknown },
+  contextId?: unknown
+): Record<string, unknown> {
+  const text = Array.isArray(result.artifacts)
+    ? result.artifacts
+        .map((a) =>
+          a && typeof a === "object" && typeof (a as { content?: unknown }).content === "string"
+            ? ((a as { content: string }).content)
+            : ""
+        )
+        .filter((s) => s.length > 0)
+        .join("\n")
+    : "";
+
+  const v1Task: Record<string, unknown> = {
+    id: task.id,
+    status: {
+      state: toV1State(task.state),
+      message: {
+        role: "ROLE_AGENT",
+        parts: [{ text, mediaType: "text/plain" }],
+      },
+    },
+    artifacts: [{ role: "ROLE_AGENT", parts: [{ text, mediaType: "text/plain" }] }],
+  };
+  if (typeof contextId === "string" && contextId) v1Task.contextId = contextId;
+  return v1Task;
+}
+
 type A2AMessage = { role: string; content: string };
 
 function toMessageArray(raw: unknown): A2AMessage[] | null {
@@ -144,7 +201,11 @@ export async function POST(req: NextRequest) {
 
   const tm = getTaskManager();
 
-  switch (method) {
+  // A2A 1.0 method-name compatibility (SendMessage → message/send, etc.)
+  const isV1Method = method in V1_METHOD_ALIASES;
+  const normalizedMethod = V1_METHOD_ALIASES[method] ?? method;
+
+  switch (normalizedMethod) {
     // ── message/send ──────────────────────────────────────
     case "message/send": {
       const skill = params?.skill || "smart-routing";
@@ -189,6 +250,15 @@ export async function POST(req: NextRequest) {
           });
         }
 
+        if (isV1Method) {
+          // A2A 1.0 SendMessageResponse — the reply text lives in
+          // task.status.message.parts (1.0 clients read it there; the v0.3
+          // top-level artifacts/metadata are not part of the 1.0 shape).
+          return jsonRpcResult(id, {
+            task: buildV1Task(task, result, params?.message?.contextId),
+          });
+        }
+
         return jsonRpcResult(id, {
           task: { id: task.id, state: "completed" },
           artifacts: result.artifacts,
diff --git a/tests/unit/a2a-v1-compat-10839.test.ts b/tests/unit/a2a-v1-compat-10839.test.ts
new file mode 100644
index 000000000000..075a3e29368d
--- /dev/null
+++ b/tests/unit/a2a-v1-compat-10839.test.ts
@@ -0,0 +1,112 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import type { NextRequest } from "next/server";
+
+const TEST_DATA_DIR = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-a2a-v1-compat-"));
+process.env.DATA_DIR = TEST_DATA_DIR;
+delete process.env.OMNIROUTE_API_KEY;
+
+const core = await import("../../src/lib/db/core.ts");
+const settingsDb = await import("../../src/lib/db/settings.ts");
+const a2aRoute = await import("../../src/app/a2a/route.ts");
+const agentCardRoute = await import("../../src/app/.well-known/agent-card.json/route.ts");
+
+function makeJsonRpcRequest(body: unknown): NextRequest {
+  return new Request("http://localhost/a2a", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  }) as unknown as NextRequest;
+}
+
+test.beforeEach(async () => {
+  core.resetDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+  fs.mkdirSync(TEST_DATA_DIR, { recursive: true });
+  await settingsDb.updateSettings({ a2aEnabled: true });
+});
+
+test.after(() => {
+  core.resetDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+});
+
+test("#10839: v1.0 SendMessage is aliased to message/send and reshapes the response", async () => {
+  const res = await a2aRoute.POST(
+    makeJsonRpcRequest({
+      jsonrpc: "2.0",
+      id: "1",
+      method: "SendMessage",
+      params: {
+        skill: "provider-discovery",
+        messages: [{ role: "user", content: "which providers support tools?" }],
+      },
+    })
+  );
+  assert.equal(res.status, 200);
+  const body = (await res.json()) as {
+    result?: { task?: { id: string; status?: { message?: { parts?: { text?: string }[] } }; artifacts?: unknown } };
+    error?: unknown;
+  };
+  assert.equal(body.error, undefined, JSON.stringify(body));
+  assert.ok(body.result?.task?.id, "v1.0 response must carry a task id");
+  const text = body.result?.task?.status?.message?.parts?.[0]?.text;
+  assert.equal(typeof text, "string");
+  assert.ok((text as string).length > 0, "task.status.message.parts[].text must carry the reply");
+  assert.ok(Array.isArray(body.result?.task?.artifacts));
+});
+
+test("#10839: v0.3 message/send keeps its existing top-level artifacts/metadata shape", async () => {
+  const res = await a2aRoute.POST(
+    makeJsonRpcRequest({
+      jsonrpc: "2.0",
+      id: "2",
+      method: "message/send",
+      params: {
+        skill: "provider-discovery",
+        messages: [{ role: "user", content: "which providers support tools?" }],
+      },
+    })
+  );
+  assert.equal(res.status, 200);
+  const body = (await res.json()) as {
+    result?: { task?: { id: string; state?: string }; artifacts?: unknown; metadata?: unknown };
+  };
+  assert.equal(body.result?.task?.state, "completed");
+  assert.ok(Array.isArray(body.result?.artifacts), "v0.3 shape must keep top-level artifacts");
+  // v0.3 responses must NOT carry the v1.0 status.message shape
+  assert.equal((body.result?.task as Record<string, unknown> | undefined)?.status, undefined);
+});
+
+test("#10839: SendStreamingMessage no longer 404s (aliased to message/stream)", async () => {
+  const res = await a2aRoute.POST(
+    makeJsonRpcRequest({
+      jsonrpc: "2.0",
+      id: "3",
+      method: "SendStreamingMessage",
+      params: {
+        skill: "provider-discovery",
+        messages: [{ role: "user", content: "hi" }],
+      },
+    })
+  );
+  assert.notEqual(res.status, 404);
+  const contentType = res.headers.get("content-type") || "";
+  assert.ok(
+    contentType.includes("text/event-stream") || res.status === 200,
+    `expected an SSE stream, got status=${res.status} content-type=${contentType}`
+  );
+});
+
+test("#10839: GET /.well-known/agent-card.json serves a v1.0 card declaring both interfaces", async () => {
+  const res = await agentCardRoute.GET();
+  assert.equal(res.status, 200);
+  const card = (await res.json()) as { supportedInterfaces?: { protocolVersion?: string }[] };
+  assert.ok(Array.isArray(card.supportedInterfaces));
+  const versions = (card.supportedInterfaces || []).map((i) => i.protocolVersion);
+  assert.ok(versions.includes("1.0"), `expected 1.0 in ${JSON.stringify(versions)}`);
+  assert.ok(versions.includes("0.3"), `expected 0.3 in ${JSON.stringify(versions)}`);
+});