diff --git a/packages/opencode/test/tool/__snapshots__/parameters.test.ts.snap b/packages/opencode/test/tool/__snapshots__/parameters.test.ts.snap
index d6c1bc45d8..9fede81759 100644
--- a/packages/opencode/test/tool/__snapshots__/parameters.test.ts.snap
+++ b/packages/opencode/test/tool/__snapshots__/parameters.test.ts.snap
@@ -319,6 +319,10 @@ exports[`tool parameters JSON Schema (wire shape) task 1`] = `
 {
   "$schema": "https://json-schema.org/draft/2020-12/schema",
   "properties": {
+    "background": {
+      "description": "When true, launch the subagent in the background and return immediately",
+      "type": "boolean",
+    },
     "command": {
       "description": "The command that triggered this task",
       "type": "string",
diff --git a/packages/opencode/test/tool/parameters.test.ts b/packages/opencode/test/tool/parameters.test.ts
index 8b2dc9a74d..3a124be81b 100644
--- a/packages/opencode/test/tool/parameters.test.ts
+++ b/packages/opencode/test/tool/parameters.test.ts
@@ -235,6 +235,10 @@ describe("tool parameters", () => {
       const parsed = parse(Task, { description: "d", prompt: "p", subagent_type: "general" })
       expect(parsed.subagent_type).toBe("general")
     })
+    test("accepts optional background flag", () => {
+      const parsed = parse(Task, { description: "d", prompt: "p", subagent_type: "general", background: true })
+      expect(parsed.background).toBe(true)
+    })
     test("rejects missing prompt", () => {
       expect(accepts(Task, { description: "d", subagent_type: "general" })).toBe(false)
     })
diff --git a/packages/opencode/test/tool/registry.test.ts b/packages/opencode/test/tool/registry.test.ts
index 5ee56300c4..3720492afe 100644
--- a/packages/opencode/test/tool/registry.test.ts
+++ b/packages/opencode/test/tool/registry.test.ts
@@ -15,7 +15,9 @@ import { Question } from "@/question"
 import { Todo } from "@/session/todo"
 import { Skill } from "@/skill"
 import { Agent } from "@/agent/agent"
+import { BackgroundJob } from "@/background/job"
 import { Session } from "@/session/session"
+import { SessionStatus } from "@/session/status"
 import { Provider } from "@/provider/provider"
 import { Git } from "@/git"
 import { LSP } from "@/lsp/lsp"
@@ -32,6 +34,7 @@ import { ToolJsonSchema } from "@/tool/json-schema"
 
 const node = CrossSpawnSpawner.defaultLayer
 const originalExperimentalScout = Flag.OPENCODE_EXPERIMENTAL_SCOUT
+const originalBackgroundAgents = Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS
 const configLayer = TestConfig.layer({
   directories: () => InstanceState.directory.pipe(Effect.map((dir) => [path.join(dir, ".opencode")])),
 })
@@ -44,6 +47,7 @@ const registryLayer = ToolRegistry.layer.pipe(
   Layer.provide(Skill.defaultLayer),
   Layer.provide(Agent.defaultLayer),
   Layer.provide(Session.defaultLayer),
+  Layer.provide(Layer.mergeAll(SessionStatus.defaultLayer, BackgroundJob.defaultLayer)),
   Layer.provide(Provider.defaultLayer),
   Layer.provide(Git.defaultLayer),
   Layer.provide(Reference.defaultLayer),
@@ -62,6 +66,7 @@ const it = testEffect(Layer.mergeAll(registryLayer, node, Agent.defaultLayer))
 
 afterEach(async () => {
   Flag.OPENCODE_EXPERIMENTAL_SCOUT = originalExperimentalScout
+  Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = originalBackgroundAgents
   await disposeAllInstances()
 })
 
@@ -88,6 +93,41 @@ describe("tool.registry", () => {
     }),
   )
 
+  it.instance("hides task_status unless experimental background agents are enabled", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = false
+      const registry = yield* ToolRegistry.Service
+      const ids = yield* registry.ids()
+
+      expect(ids).not.toContain("task_status")
+    }),
+  )
+
+  it.instance("hides task background parameter unless experimental background agents are enabled", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = false
+      const registry = yield* ToolRegistry.Service
+      const agent = yield* Agent.Service
+      const build = yield* agent.get("build")
+      const task = (yield* registry.tools({ providerID: ProviderID.opencode, modelID: ModelID.make("test"), agent: build })).find(
+        (tool) => tool.id === "task",
+      )
+
+      expect(task?.jsonSchema).toBeDefined()
+      expect((task?.jsonSchema?.properties as Record<string, unknown> | undefined)?.background).toBeUndefined()
+    }),
+  )
+
+  it.instance("shows task_status when experimental background agents are enabled", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = true
+      const registry = yield* ToolRegistry.Service
+      const ids = yield* registry.ids()
+
+      expect(ids).toContain("task_status")
+    }),
+  )
+
   it.instance("loads tools from .opencode/tool (singular)", () =>
     Effect.gen(function* () {
       const test = yield* TestInstance
diff --git a/packages/opencode/test/tool/task.test.ts b/packages/opencode/test/tool/task.test.ts
index f75fcf84b8..5aa6f5f560 100644
--- a/packages/opencode/test/tool/task.test.ts
+++ b/packages/opencode/test/tool/task.test.ts
@@ -1,20 +1,28 @@
 import { afterEach, describe, expect } from "bun:test"
 import { Effect, Exit, Fiber, Layer } from "effect"
 import { Agent } from "../../src/agent/agent"
+import { BackgroundJob } from "@/background/job"
+import { Bus } from "@/bus"
 import { Config } from "@/config/config"
 import { CrossSpawnSpawner } from "@opencode-ai/core/cross-spawn-spawner"
 import { Session } from "@/session/session"
 import { MessageV2 } from "../../src/session/message-v2"
 import type { SessionPrompt } from "../../src/session/prompt"
 import { MessageID, PartID, SessionID } from "../../src/session/schema"
+import { SessionRunState } from "@/session/run-state"
+import { SessionStatus } from "@/session/status"
 import { ModelID, ProviderID } from "../../src/provider/schema"
 import { TaskTool, type TaskPromptOps } from "../../src/tool/task"
 import { Truncate } from "@/tool/truncate"
 import { ToolRegistry } from "@/tool/registry"
+import { Flag } from "@opencode-ai/core/flag/flag"
 import { disposeAllInstances } from "../fixture/fixture"
 import { testEffect } from "../lib/effect"
 
+const originalBackgroundAgents = Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS
+
 afterEach(async () => {
+  Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = originalBackgroundAgents
   await disposeAllInstances()
 })
 
@@ -26,9 +34,13 @@ const ref = {
 const it = testEffect(
   Layer.mergeAll(
     Agent.defaultLayer,
+    BackgroundJob.defaultLayer,
+    Bus.defaultLayer,
     Config.defaultLayer,
     CrossSpawnSpawner.defaultLayer,
     Session.defaultLayer,
+    SessionRunState.defaultLayer,
+    SessionStatus.defaultLayer,
     Truncate.defaultLayer,
     ToolRegistry.defaultLayer,
   ),
@@ -80,6 +92,7 @@ function stubOps(opts?: { onPrompt?: (input: SessionPrompt.PromptInput) => void;
         opts?.onPrompt?.(input)
         return reply(input, opts?.text ?? "done")
       }),
+    loop: (input) => Effect.succeed(reply({ sessionID: input.sessionID, parts: [] }, opts?.text ?? "done")),
   }
 }
 
@@ -294,6 +307,7 @@ describe("tool.task", () => {
             ready.resolve(input)
             return cancelled.promise
           }).pipe(Effect.as(reply(input, "cancelled"))),
+        loop: (input) => Effect.succeed(reply({ sessionID: input.sessionID, parts: [] }, "done")),
       }
 
       const fiber = yield* def
@@ -432,4 +446,318 @@ describe("tool.task", () => {
       },
     },
   )
+
+  it.instance("rejects background execution when the experiment is disabled", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = false
+      const { chat, assistant } = yield* seed()
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+
+      const exit = yield* def
+        .execute(
+          {
+            description: "inspect bug",
+            prompt: "look into the cache key path",
+            subagent_type: "general",
+            background: true,
+          },
+          {
+            sessionID: chat.id,
+            messageID: assistant.id,
+            agent: "build",
+            abort: new AbortController().signal,
+            extra: { promptOps: stubOps() },
+            messages: [],
+            metadata: () => Effect.void,
+            ask: () => Effect.void,
+          },
+        )
+        .pipe(Effect.exit)
+
+      expect(Exit.isFailure(exit)).toBe(true)
+    }),
+  )
+
+  it.instance("execute launches background tasks without waiting for completion", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = true
+      const jobs = yield* BackgroundJob.Service
+      const { chat, assistant } = yield* seed()
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+
+      const result = yield* def.execute(
+        {
+          description: "inspect bug",
+          prompt: "look into the cache key path",
+          subagent_type: "general",
+          background: true,
+        },
+        {
+          sessionID: chat.id,
+          messageID: assistant.id,
+          agent: "build",
+          abort: new AbortController().signal,
+          extra: {
+            promptOps: {
+              ...stubOps(),
+              prompt: () => Effect.never,
+            } satisfies TaskPromptOps,
+          },
+          messages: [],
+          metadata: () => Effect.void,
+          ask: () => Effect.void,
+        },
+      )
+
+      const job = yield* jobs.get(result.metadata.sessionId)
+      expect(result.metadata.background).toBe(true)
+      expect(result.output).toContain("state: running")
+      expect(job?.status).toBe("running")
+    }),
+  )
+
+  it.instance("background tasks complete through the background job service", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = true
+      const jobs = yield* BackgroundJob.Service
+      const { chat, assistant } = yield* seed()
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+
+      const result = yield* def.execute(
+        {
+          description: "inspect bug",
+          prompt: "look into the cache key path",
+          subagent_type: "general",
+          background: true,
+        },
+        {
+          sessionID: chat.id,
+          messageID: assistant.id,
+          agent: "build",
+          abort: new AbortController().signal,
+          extra: { promptOps: stubOps({ text: "background done" }) },
+          messages: [],
+          metadata: () => Effect.void,
+          ask: () => Effect.void,
+        },
+      )
+
+      const waited = yield* jobs.wait({ id: result.metadata.sessionId, timeout: 1_000 })
+      expect(waited.timedOut).toBe(false)
+      expect(waited.info?.status).toBe("completed")
+      expect(waited.info?.output).toBe("background done")
+    }),
+  )
+
+  it.instance("background task completion does not wait for the parent resume loop", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = true
+      const jobs = yield* BackgroundJob.Service
+      const sessions = yield* Session.Service
+      const { chat, assistant } = yield* seed()
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+
+      const result = yield* def.execute(
+        {
+          description: "inspect bug",
+          prompt: "look into the cache key path",
+          subagent_type: "general",
+          background: true,
+        },
+        {
+          sessionID: chat.id,
+          messageID: assistant.id,
+          agent: "build",
+          abort: new AbortController().signal,
+          extra: {
+            promptOps: {
+              ...stubOps({ text: "background done" }),
+              prompt: (input) =>
+                input.noReply
+                  ? Effect.gen(function* () {
+                      const user = yield* sessions.updateMessage({
+                        id: input.messageID ?? MessageID.ascending(),
+                        role: "user",
+                        sessionID: input.sessionID,
+                        agent: input.agent ?? "build",
+                        model: input.model ?? ref,
+                        time: { created: Date.now() },
+                      })
+                      const parts = input.parts.map((part) => ({
+                        ...part,
+                        id: part.id ?? PartID.ascending(),
+                        messageID: user.id,
+                        sessionID: input.sessionID,
+                      }))
+                      yield* Effect.forEach(parts, (part) => sessions.updatePart(part), { discard: true })
+                      return { info: user, parts }
+                    })
+                  : Effect.succeed(reply(input, "background done")),
+              loop: () => Effect.never,
+            } satisfies TaskPromptOps,
+          },
+          messages: [],
+          metadata: () => Effect.void,
+          ask: () => Effect.void,
+        },
+      )
+
+      const waited = yield* jobs.wait({ id: result.metadata.sessionId, timeout: 1_000 })
+      expect(waited.timedOut).toBe(false)
+      expect(waited.info?.status).toBe("completed")
+    }),
+  )
+
+  it.instance("removing the parent session cancels running background tasks", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = true
+      const jobs = yield* BackgroundJob.Service
+      const sessions = yield* Session.Service
+      const { chat, assistant } = yield* seed()
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+
+      const result = yield* def.execute(
+        {
+          description: "inspect bug",
+          prompt: "look into the cache key path",
+          subagent_type: "general",
+          background: true,
+        },
+        {
+          sessionID: chat.id,
+          messageID: assistant.id,
+          agent: "build",
+          abort: new AbortController().signal,
+          extra: {
+            promptOps: {
+              ...stubOps(),
+              prompt: () => Effect.never,
+            } satisfies TaskPromptOps,
+          },
+          messages: [],
+          metadata: () => Effect.void,
+          ask: () => Effect.void,
+        },
+      )
+
+      yield* sessions.remove(chat.id)
+      const waited = yield* jobs.wait({ id: result.metadata.sessionId, timeout: 1_000 })
+      expect(waited.timedOut).toBe(false)
+      expect(waited.info?.status).toBe("cancelled")
+    }),
+  )
+
+  it.instance("removing the child task session cancels its running background task", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = true
+      const jobs = yield* BackgroundJob.Service
+      const sessions = yield* Session.Service
+      const { chat, assistant } = yield* seed()
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+
+      const result = yield* def.execute(
+        {
+          description: "inspect bug",
+          prompt: "look into the cache key path",
+          subagent_type: "general",
+          background: true,
+        },
+        {
+          sessionID: chat.id,
+          messageID: assistant.id,
+          agent: "build",
+          abort: new AbortController().signal,
+          extra: {
+            promptOps: {
+              ...stubOps(),
+              prompt: () => Effect.never,
+            } satisfies TaskPromptOps,
+          },
+          messages: [],
+          metadata: () => Effect.void,
+          ask: () => Effect.void,
+        },
+      )
+
+      yield* sessions.remove(result.metadata.sessionId)
+      const waited = yield* jobs.wait({ id: result.metadata.sessionId, timeout: 1_000 })
+      expect(waited.timedOut).toBe(false)
+      expect(waited.info?.status).toBe("cancelled")
+    }),
+  )
+
+  it.instance("cancelling the parent run cancels running background tasks", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = true
+      const jobs = yield* BackgroundJob.Service
+      const runState = yield* SessionRunState.Service
+      const { chat, assistant } = yield* seed()
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+
+      const result = yield* def.execute(
+        {
+          description: "inspect bug",
+          prompt: "look into the cache key path",
+          subagent_type: "general",
+          background: true,
+        },
+        {
+          sessionID: chat.id,
+          messageID: assistant.id,
+          agent: "build",
+          abort: new AbortController().signal,
+          extra: {
+            promptOps: {
+              ...stubOps(),
+              prompt: () => Effect.never,
+            } satisfies TaskPromptOps,
+          },
+          messages: [],
+          metadata: () => Effect.void,
+          ask: () => Effect.void,
+        },
+      )
+
+      yield* runState.cancel(chat.id)
+      const waited = yield* jobs.wait({ id: result.metadata.sessionId, timeout: 1_000 })
+      expect(waited.timedOut).toBe(false)
+      expect(waited.info?.status).toBe("cancelled")
+    }),
+  )
+
+  it.instance("cancelling a parent run recursively cancels descendant background tasks", () =>
+    Effect.gen(function* () {
+      const jobs = yield* BackgroundJob.Service
+      const runState = yield* SessionRunState.Service
+      const sessions = yield* Session.Service
+      const { chat } = yield* seed()
+      const child = yield* sessions.create({ parentID: chat.id, title: "child" })
+      const grandchild = yield* sessions.create({ parentID: child.id, title: "grandchild" })
+
+      yield* jobs.start({
+        id: child.id,
+        type: "task",
+        metadata: { parentSessionId: chat.id, sessionId: child.id },
+        run: Effect.never,
+      })
+      yield* jobs.start({
+        id: grandchild.id,
+        type: "task",
+        metadata: { parentSessionId: child.id, sessionId: grandchild.id },
+        run: Effect.never,
+      })
+
+      yield* runState.cancel(chat.id)
+
+      expect((yield* jobs.get(child.id))?.status).toBe("cancelled")
+      expect((yield* jobs.get(grandchild.id))?.status).toBe("cancelled")
+    }),
+  )
 })
diff --git a/packages/opencode/test/tool/task_status.test.ts b/packages/opencode/test/tool/task_status.test.ts
new file mode 100644
index 0000000000..448f24e766
--- /dev/null
+++ b/packages/opencode/test/tool/task_status.test.ts
@@ -0,0 +1,95 @@
+import { afterEach, describe, expect } from "bun:test"
+import { Effect, Layer } from "effect"
+import { Agent } from "@/agent/agent"
+import { BackgroundJob } from "@/background/job"
+import { Bus } from "@/bus"
+import { CrossSpawnSpawner } from "@opencode-ai/core/cross-spawn-spawner"
+import { Session } from "@/session/session"
+import { MessageID } from "@/session/schema"
+import { SessionStatus } from "@/session/status"
+import { TaskStatusTool } from "@/tool/task_status"
+import { Truncate } from "@/tool/truncate"
+import { Flag } from "@opencode-ai/core/flag/flag"
+import { disposeAllInstances } from "../fixture/fixture"
+import { testEffect } from "../lib/effect"
+
+const originalBackgroundAgents = Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS
+
+afterEach(async () => {
+  Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = originalBackgroundAgents
+  await disposeAllInstances()
+})
+
+const it = testEffect(
+  Layer.mergeAll(
+    Agent.defaultLayer,
+    BackgroundJob.defaultLayer,
+    Bus.defaultLayer,
+    CrossSpawnSpawner.defaultLayer,
+    Session.defaultLayer,
+    SessionStatus.defaultLayer,
+    Truncate.defaultLayer,
+  ),
+)
+
+describe("tool.task_status", () => {
+  it.instance("returns completed background job output", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = true
+      const jobs = yield* BackgroundJob.Service
+      const sessions = yield* Session.Service
+      const tool = yield* TaskStatusTool
+      const def = yield* tool.init()
+      const chat = yield* sessions.create({})
+
+      yield* jobs.start({ id: chat.id, type: "task", run: Effect.succeed("all done") })
+
+      const result = yield* def.execute(
+        { task_id: chat.id, wait: true, timeout_ms: 1_000 },
+        {
+          sessionID: chat.id,
+          messageID: MessageID.ascending(),
+          agent: "build",
+          abort: new AbortController().signal,
+          messages: [],
+          metadata: () => Effect.void,
+          ask: () => Effect.void,
+        },
+      )
+
+      expect(result.output).toContain("state: completed")
+      expect(result.output).toContain("all done")
+      expect(result.metadata.timed_out).toBe(false)
+    }),
+  )
+
+  it.instance("wait=true times out while the background job is running", () =>
+    Effect.gen(function* () {
+      Flag.OPENCODE_EXPERIMENTAL_BACKGROUND_AGENTS = true
+      const jobs = yield* BackgroundJob.Service
+      const sessions = yield* Session.Service
+      const tool = yield* TaskStatusTool
+      const def = yield* tool.init()
+      const chat = yield* sessions.create({})
+
+      yield* jobs.start({ id: chat.id, type: "task", run: Effect.never })
+
+      const result = yield* def.execute(
+        { task_id: chat.id, wait: true, timeout_ms: 50 },
+        {
+          sessionID: chat.id,
+          messageID: MessageID.ascending(),
+          agent: "build",
+          abort: new AbortController().signal,
+          messages: [],
+          metadata: () => Effect.void,
+          ask: () => Effect.void,
+        },
+      )
+
+      expect(result.output).toContain("state: running")
+      expect(result.output).toContain("Timed out after 50ms")
+      expect(result.metadata.timed_out).toBe(true)
+    }),
+  )
+})