Creating Ephemeral (Stateless) Agents (TypeScript)

Overview

An ephemeral agent is a Golem agent that gets a fresh instance for every invocation. Unlike the default durable agents, ephemeral agents:

• No shared state: Each invocation starts from a fresh init() call — state set in one call is gone by the next
• No method recovery replay: An oplog is still recorded lazily (useful for debugging via golem agent oplog). If the executor restarts while preparing an invocation, Golem can replay the recorded initialization so that the method can still start. Once the method starts, a failure is terminal; Golem does not replay the method.
• No persistence: The agent’s memory is discarded after each invocation completes
• Logical target versus concrete identity: The id record selects the logical target; each call uses a fresh, one-shot concrete agent identity

This makes ephemeral agents ideal for pure request handlers, stateless transformers, adapters, and serverless-style functions where each call is independent.

How to Create an Ephemeral Agent

Set mode: 'ephemeral' on the defineAgent(...) spec:

import { z } from 'zod';
import { defineAgent, method } from '@golemcloud/golem-ts-sdk';
 
export const RequestHandler = defineAgent({
    name: 'RequestHandler',
    mode: 'ephemeral',
    id: { name: z.string() },
    methods: {
        handle: method({ input: { input: z.string() }, returns: z.string() }),
    },
});
 
export const RequestHandlerImpl = RequestHandler.implement({
    init: () => ({}),
    methods: {
        handle({ input }) {
            return `processed: ${input}`;
        },
    },
});

What “Fresh Instance Per Invocation” Means

Consider a durable agent vs an ephemeral one:

// DURABLE (default) — state accumulates across calls
export const DurableCounter = defineAgent({
    name: 'DurableCounter',
    id: { name: z.string() },
    methods: { increment: method({ input: {}, returns: z.number() }) },
});
DurableCounter.implement({
    init: () => ({ count: 0 }),
    methods: {
        increment() {
            this.count += 1;
            return this.count;
        },
    },
});
// Call increment() three times → returns 1, 2, 3
 
// EPHEMERAL — state resets every call
export const EphemeralCounter = defineAgent({
    name: 'EphemeralCounter',
    mode: 'ephemeral',
    id: { name: z.string() },
    methods: { increment: method({ input: {}, returns: z.number() }) },
});
EphemeralCounter.implement({
    init: () => ({ count: 0 }),
    methods: {
        increment() {
            this.count += 1;
            return this.count;
        },
    },
});
// Call increment() three times → returns 1, 1, 1

Each invocation of an ephemeral agent:

1. Creates a fresh instance via init()
2. Executes the method
3. Discards the instance entirely

Combining with HTTP Endpoints

Ephemeral agents are a natural fit for HTTP request handlers. Declare an http mount on the agent and an http endpoint on each method:

import { z } from 'zod';
import { defineAgent, method, http } from '@golemcloud/golem-ts-sdk';
 
export const ConverterAgent = defineAgent({
    name: 'ConverterAgent',
    mode: 'ephemeral',
    id: { name: z.string() },
    http: http.mount('/api/convert/{name}'),
    methods: {
        toUpper: method({ input: { input: z.string() }, returns: z.string(), http: http.post('/to-upper') }),
        toLower: method({ input: { input: z.string() }, returns: z.string(), http: http.post('/to-lower') }),
    },
});
 
export const ConverterAgentImpl = ConverterAgent.implement({
    init: () => ({}),
    methods: {
        toUpper({ input }) {
            return input.toUpperCase();
        },
        toLower({ input }) {
            return input.toLowerCase();
        },
    },
});

When to Use Ephemeral Agents

When NOT to Use Ephemeral Agents

• Counters, accumulators, shopping carts — need state across calls → use durable (default)
• Workflow orchestrators, sagas — need oplog for recovery → use durable (default)
• Agents calling external APIs where at-least-once semantics matter → use durable (default)
• Any agent where one call’s result depends on a previous call → use durable (default)

Key Points

• Ephemeral mode is set at the agent type level via mode: 'ephemeral' — all instances of the type are ephemeral
• The id record defines the logical target, not a reusable concrete instance across calls
• Ephemeral agents can call other agents via RPC and make HTTP requests, but do not support durable suspension or unlimited waits
• The oplog is still recorded lazily, so you can inspect what an ephemeral agent did via golem agent oplog. If the executor restarts while preparing an invocation, Golem can replay the recorded initialization so that the method can still start. Once the method starts, a failure is terminal; Golem does not replay the method.