Stateless vs. Stateful: The Memory Trade-off

One of the deepest technical decisions you will make as an agentic engineer is how to handle State. In the world of StrandAgents and event-driven systems, this choice determines how you scale.

1. The Stateless Agent

A stateless agent treats every event as if it is the "first time" it has ever seen the user.

• How it works: Every event must contain all the context needed to solve it.
• Pros: Incredibly easy to scale (Serverless). Low latency. No database lock issues.
• Cons: If the conversation is 20 messages long, the "Event" becomes massive because you have to include all 20 messages every time.

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2. The Stateful Agent

A stateful agent (like LangGraph) remembers the session.

• How it works: The agent receives an "ID." It looks up the user's history in a database before thinking.
• Pros: Cleaner events. Better for long-running user relationships.
• Cons: Slower (DB lookup latency). Harder to scale (you have to worry about "Race conditions" if two events hit the same state at once).

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3. Comparison Matrix

Feature	Stateless	Stateful
Storage	None (Transient)	Database (Persistent)
Payload Size	Large (Contains history)	Small (Contains ID)
Complexity	Low	High
Ideal For	Classification, Translation, Summarization	Personal Assistants, RPG Bots, Coding Agents

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4. Visualizing the Payload Shift

Stateless Event Payload:

{
  "event": "new_message",
  "history": [
    {"user": "Hi"},
    {"bot": "Hello, how can I help?"}
  ],
  "new_input": "What's the weather?"
}

Stateful Event Payload:

{
  "event": "new_message",
  "thread_id": "session_8892",
  "new_input": "What's the weather?"
}

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5. The "Hybrid" Approach (Strand Pattern)

StrandAgents often use a hybrid:

1. The Dispatcher is stateless (handles 10,000 requests/sec).
2. It routes to a Worker which is stateful (loads the context for one specific user).

This gives you the reliability of a stateful system with the scale of a stateless one.

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Key Takeaways

• Stateless is for high-speed, independent tasks.
• Stateful is for multi-turn conversations and long-running workflows.
• Context window limits are the primary reason to move from stateless to stateful as conversations grow.
• Threading and Locking are the primary challenges of stateful multi-agent systems.