Letta + Fable 5: Persistent Memory for Multi-Week Projects

The Stack

Tested Against

Prerequisites

• Python (pip install letta-client)
• A running Letta server (self-hosted or Letta Cloud) and LETTA_API_KEY
• An Anthropic API key for anthropic/claude-fable-5

Steps

1. 1

   Create a Letta agent on Fable with memory blocks

   pip install letta-client. Then client.agents.create(model='anthropic/claude-fable-5', memory_blocks=[{label:'human', value:'...'}, {label:'persona', value:'...'}]). The agent reads and rewrites those blocks over time, so it remembers across restarts.

2. 2

   What CI checks: the agent config is valid and names Fable

   CI confirms the agent config dict is valid, model equals anthropic/claude-fable-5, and the required human and persona memory blocks are present and non-empty. Deterministic, no key. The recall and self-editing are fenced.

   cat > letta-agent.json <<'EOF'
   {
     "model": "anthropic/claude-fable-5",
     "memory_blocks": [
       { "label": "human", "value": "Lead engineer migrating a monolith to services." },
       { "label": "persona", "value": "I am a long-horizon coding agent. I keep notes and update them." }
     ]
   }
   EOF
   cat > checkletta.mjs <<'EOF'
   import { readFileSync } from 'node:fs';
   const cfg = JSON.parse(readFileSync('letta-agent.json', 'utf8'));
   let ok = true;
   function check(label, cond){ console.log(label + ': ' + (cond ? 'yes' : 'NO')); if(!cond) ok=false; }
   check('agent config parses', true);
   check('model is anthropic/claude-fable-5', cfg.model === 'anthropic/claude-fable-5');
   const blocks = cfg.memory_blocks || [];
   const by = Object.fromEntries(blocks.map(b => [b.label, (b.value || '').trim()]));
   check('human memory block present and non-empty', !!by.human && by.human.length > 0);
   check('persona memory block present and non-empty', !!by.persona && by.persona.length > 0);
   if(!ok){ console.log('letta agent config check FAILED'); process.exit(1); }
   console.log('letta agent config check OK: anthropic/claude-fable-5 + human/persona blocks');
   EOF
   node checkletta.mjs

3. 3

   Run it across sessions (the model step, not checked by CI)

   Send messages over days or weeks; Fable recalls and updates its memory blocks. That runs the model and is non-deterministic, so CI never claims it. The badge covers the agent config, not the recall.