DurableAgent

DurableAgent wraps an existing Agent with durable execution and resumable streams. It runs the agentic loop so that a client can disconnect and reconnect without missing events, and it streams those events over PubSub. Use it when a run must outlive a single request or survive a dropped connection.

Create one with the createDurableAgent factory, or use createEventedAgent for fire-and-forget execution on the built-in workflow engine. For Inngest-powered execution, use createInngestAgent from @mastra/inngest.

Usage example

src/mastra/index.ts

import { Mastra } from '@mastra/core'
import { Agent } from '@mastra/core/agent'
import { createDurableAgent } from '@mastra/core/agent/durable'

const agent = new Agent({
  id: 'my-agent',
  name: 'My Agent',
  instructions: 'You are a helpful assistant',
  model: 'openai/gpt-5.5',
})

const durableAgent = createDurableAgent({ agent })

export const mastra = new Mastra({
  agents: { myAgent: durableAgent },
})

Stream a response and read the result. The cleanup function unsubscribes from PubSub when you are done with the run:

const { output, runId, cleanup } = await durableAgent.stream('Hello!')

const text = await output.text

cleanup()

createDurableAgent(options)

Wraps an Agent with durable execution and resumable streams. This is the recommended way to create a DurableAgent.

import { createDurableAgent } from '@mastra/core/agent/durable'

const durableAgent = createDurableAgent({ agent })

Returns: DurableAgent

Parameters

agent:

Agent

The Agent to wrap with durable execution capabilities. Agent methods delegate to this agent.

id?:

string

= agent.id

ID override.

name?:

string

= agent.name

Name override.

cache?:

MastraServerCache | false

Cache for stored stream events, which enables resumable streams. If omitted, the agent inherits the cache from the Mastra instance, or uses an InMemoryServerCache. Set to false to disable caching, which makes streams non-resumable.

pubsub?:

PubSub

= EventEmitterPubSub

PubSub instance for streaming events.

maxSteps?:

number

Maximum number of steps for the agentic loop.

createEventedAgent(options)

Wraps an Agent with fire-and-forget durable execution on the built-in workflow engine. Like createDurableAgent, it returns a result you stream from, but the underlying workflow runs non-blocking (via startAsync) instead of running to completion before the stream is wired up. Use it when you want the run to progress independently of the caller. It doesn't accept id or name overrides.

import { createEventedAgent } from '@mastra/core/agent/durable'

const eventedAgent = createEventedAgent({ agent })

Returns: EventedAgent (a subclass of DurableAgent)

Parameters

agent:

Agent

The Agent to wrap with evented durable execution capabilities.

cache?:

MastraServerCache | false

Cache for stored stream events, which enables resumable streams. If omitted, the agent inherits the cache from the Mastra instance, or uses an InMemoryServerCache. Set to false to disable caching.

pubsub?:

PubSub

= EventEmitterPubSub

PubSub instance for streaming events.

maxSteps?:

number

Maximum number of steps for the agentic loop.

Constructor parameters

The DurableAgent class accepts the same options as createDurableAgent, plus cleanupTimeoutMs. Prefer the factory unless you need to subclass.

agent:

Agent

The Agent to wrap with durable execution capabilities.

id?:

string

= agent.id

ID override.

name?:

string

= agent.name

Name override.

cache?:

MastraServerCache | false

Cache for stored stream events. If omitted, inherits from the Mastra instance or uses an InMemoryServerCache. Set to false to disable caching.

pubsub?:

PubSub

= EventEmitterPubSub

PubSub instance for streaming events.

maxSteps?:

number

Maximum number of steps for the agentic loop.

cleanupTimeoutMs?:

number

= 30000

Grace period in milliseconds before registry entries are cleaned up automatically after a stream finishes or errors. Set to 0 to disable auto-cleanup and require a manual cleanup() call. Auto-cleanup does not fire on suspended events.

Methods

Execution

stream(messages, options?)

Streams a response using durable execution. Returns immediately with a result whose output produces events as the run progresses.

const { output, runId, cleanup } = await durableAgent.stream('Hello!', {
  onChunk: chunk => console.log(chunk),
  onFinish: result => console.log('done', result),
})

const text = await output.text
cleanup()

Returns: Promise<DurableAgentStreamResult>

resume(runId, resumeData, options?)

Resumes a suspended run, for example after a tool approval. Pass the runId from the original stream and the data the run was waiting on. Throws if no registry entry exists for the run.

const { output, cleanup } = await durableAgent.resume(runId, {
  approved: true,
})

await output.text
cleanup()

Returns: Promise<DurableAgentStreamResult>

observe(runId, options?)

Reconnects to an existing run, replaying cached events before delivering live ones. Use this after a network disconnection. Pass offset to start replay from a known position.

const { output, cleanup } = await durableAgent.observe(runId, {
  offset: 0,
  onChunk: chunk => console.log(chunk),
})

await output.text

Returns: Promise<DurableAgentStreamResult>

warning

The cleanup() returned by observe() destroys the run's registry entries and cached events. Only call it when you are done with the run. If the run is suspended and you intend to resume later, don't call cleanup() — let the auto-cleanup timer handle it after the run finishes or errors. Auto-cleanup doesn't fire on suspended events.

prepare(messages, options?)

Prepares a run for durable execution without starting it. Registers the run in the internal registry and returns the serialized workflow input. Use this when you need to control when and how the workflow is triggered.

const { runId, messageId, workflowInput, threadId, resourceId } = await durableAgent.prepare(
  'Summarize the document',
  {
    memory: { threadId: 'thread-1', resourceId: 'user-1' },
  },
)

Returns:

interface PrepareResult {
  runId: string
  messageId: string
  workflowInput: any
  registryEntry: object
  threadId?: string
  resourceId?: string
}

Stream options

stream() accepts a DurableAgentStreamOptions object. It supports the agent execution options below, plus lifecycle callbacks.

runId?:

string

Unique identifier for this run. Use it later with resume() or observe().

instructions?:

AgentExecutionOptions['instructions']

Overrides the agent's default instructions for this run. Accepts a static string or the same dynamic instructions value the agent supports.

context?:

ModelMessage[]

Additional context messages to provide to the agent.

memory?:

object

Memory configuration for conversation persistence and retrieval.

requestContext?:

RequestContext

Request context carrying dynamic configuration and state for this run.

maxSteps?:

number

Maximum number of steps to run for this stream.

toolsets?:

object

Additional tool sets available for this run.

clientTools?:

object

Client-side tools available during execution.

toolChoice?:

'auto' | 'none' | 'required' | { type: 'tool'; toolName: string }

Tool selection strategy.

activeTools?:

string[]

Restricts execution to the named subset of the agent's tools.

modelSettings?:

object

Model-specific settings such as temperature. Credential-bearing headers (Authorization, X-Api-Key, and similar) are stripped from the serialized snapshot before it crosses process boundaries.

stopWhen?:

AgentExecutionOptions['stopWhen']

Predicate or composition that ends the agentic loop early. The closure rides on the in-process run registry; cross-process resumes degrade to maxSteps only.

system?:

string | string[]

Additional system message appended after the agent instructions and before user messages.

requireToolApproval?:

boolean | ((args: { toolName: string; args: unknown; requestContext: RequestContext; workspace?: string }) => boolean | Promise<boolean>)

Require approval for tool calls. Pass true or false to gate all or none, or a function for per-call policy. Function-form policies live on the in-process run registry; cross-process resumes fall back to a true shadow.

autoResumeSuspendedTools?:

boolean

Automatically resume tools that suspended, instead of waiting for an external resume() call.

toolCallConcurrency?:

number

Maximum number of tool calls to execute concurrently.

includeRawChunks?:

boolean

Include raw provider chunks in the stream output.

maxProcessorRetries?:

number

Maximum number of processor retries per generation.

structuredOutput?:

object

Structured output configuration.

untilIdle?:

boolean | { maxIdleMs?: number }

When set, keeps the stream open across background-task continuations until the agent is idle. Pass true for the default 5-minute idle timeout, or { maxIdleMs } to customise. Equivalent to the deprecated streamUntilIdle() method. Also supported on resume().

disableBackgroundTasks?:

boolean

Disable background-task dispatch for this run. Background-eligible tools execute inline instead.

tracingOptions?:

AgentExecutionOptions['tracingOptions']

Tracing metadata, tags, trace ID, parent span ID, and requestContextKeys forwarded to the agent and model spans. Fully JSON-serializable.

actor?:

AgentExecutionOptions['actor']

Per-call actor signal forwarded to FGA checks and tool execution.

transform?:

AgentExecutionOptions['transform']

Per-invocation tool payload transform policy. The transformToolPayload closure lives on the in-process run registry; only the JSON-safe targets shadow is serialized.

prepareStep?:

AgentExecutionOptions['prepareStep']

Per-step preparation hook invoked as a PrepareStepProcessor at the start of every iteration. Closure-only — stored on the in-process run registry. Cross-process resumes lose the hook.

isTaskComplete?:

AgentExecutionOptions['isTaskComplete']

Per-call completion policy. Scorer instances and onComplete live on the in-process run registry; the JSON-safe primitives (strategy, timeout, parallel, suppressFeedback, scorerNames) are serialized for cross-process observability.

delegation?:

AgentExecutionOptions['delegation']

Sub-agent delegation hooks (onDelegationStart, onDelegationComplete, messageFilter). Callbacks are baked into the sub-agent tool wrappers at prepare time. Cross-process resumes lose the callbacks.

versions?:

object

Version overrides for sub-agent delegation.

abortSignal?:

AbortSignal

External abort signal. Forwarded to the durable run's internal AbortController, so either source can cancel the run. Cross-process resumes cannot recover the signal — pass a fresh one to resume() if you need post-resume abortability.

onChunk?:

(chunk: ChunkType) => void | Promise<void>

Called for each streamed chunk.

onStepFinish?:

(result: AgentStepFinishEventData) => void | Promise<void>

Called when a step in the agentic loop finishes.

onFinish?:

(result: AgentFinishEventData) => void | Promise<void>

Called when the run finishes.

onError?:

(error: Error) => void | Promise<void>

Called when the run errors.

onSuspended?:

(data: AgentSuspendedEventData) => void | Promise<void>

Called when the run suspends, for example for tool approval.

onAbort?:

AgentExecutionOptions['onAbort']

Called when the run is aborted via abortSignal or result.abort().

onIterationComplete?:

AgentExecutionOptions['onIterationComplete']

Called after every agentic-loop iteration with the latest messageList, finishReason, and isFinal flag. Observation-only on durable agents: returning continue: false or feedback does not influence the loop.

resume() and observe() accept the same lifecycle callbacks (onChunk, onStepFinish, onFinish, onError, onSuspended). observe() also accepts an offset to control where replay starts.

DurableAgentStreamResult

The object returned by stream(), resume(), and observe().

interface DurableAgentStreamResult<OUTPUT = undefined> {
  output: MastraModelOutput<OUTPUT>
  readonly fullStream: ReadableStream<any>
  runId: string
  threadId?: string
  resourceId?: string
  cleanup: () => void
  abort: () => void
}

output:

MastraModelOutput

The streaming output. Await output.text for the full text, or consume output.fullStream.

fullStream:

ReadableStream

The full event stream, delegating to output.fullStream.

runId:

string

The unique run ID. Pass it to resume() or observe() to reconnect.

threadId?:

string

Thread ID when using memory.

resourceId?:

string

Resource ID when using memory.

cleanup:

() => void

Unsubscribes from PubSub and clears registry entries for the run. Call it when done with the run.

abort:

() => void

Aborts the run by flipping the internal AbortController. Surfaces as an AbortError inside the durable LLM-execution step and fires the onAbort callback. Safe to call after the run has finished — a no-op in that case.

Related

• createInngestAgent()
• Agent class
• PubSub
• .getMemory()