## TL;DR

Size your blocks deliberately: raise limits only for blocks that earn the context, and keep the sum of all blocks well under the model's window or Letta refuses to run. When seeding values, use templates so every agent starts consistent. If an agent reports it cannot update its memory, check whether its old_content matched the block exactly, and consider the newer patch-style memory tools that avoid fragile exact-match replacements.

## Fix

Size your blocks deliberately: raise limits only for blocks that earn the context, and keep the sum of all blocks well under the model's window or Letta refuses to run. When seeding values, use templates so every agent starts consistent. If an agent reports it cannot update its memory, check whether its old_content matched the block exactly, and consider the newer patch-style memory tools that avoid fragile exact-match replacements.

Context: A Letta deep-dive documents the core memory sizing trap. Every block defaults to a 2000 character limit, configurable per block, but all blocks combined plus the instructions plus the conversation must fit in the model's context window, and Letta warns or errors when total core memory would overflow it. A second gotcha: the agent edits blocks with core_memory_replace using exact string matching, so if the old_content is off by even one character the replacement fails and the agent must retry.

## Matched source
Source: Published skill
Original query: "Letta core memory blocks default to 2000 chars and must all fit in context"
Key terms: 2000, blocks, chars, context, core, default, letta, memory, must

## When to use this

- Use this when your task, error, or question matches the title above and the setup in the Fix section.

## When not to use this

- Skip it when the error text, tool, or situation is different. Forcing a mismatched fix usually costs more time than searching again.

## Compatibility

The original write-up does not pin tool versions. Treat the commands and UI paths above as reflecting the author's setup, and check your tool's own docs if your version looks different.

---

## Vectle citations

- Exact version: <https://vectle.com/skills/skl_zo045mIsobAYHm_nEohJSA/versions/skv_kNg2mzmUo2EBc2ZyuPO2-w>
- Canonical HTML skill page: <https://vectle.com/skills/skl_zo045mIsobAYHm_nEohJSA>
- Current Markdown URL: <https://vectle.com/skills/skl_zo045mIsobAYHm_nEohJSA/markdown>

## Selected public attribution and original notices/references

```json
{
  "author": "issueatlas",
  "client": null,
  "notices_and_references": [
    "https://github.com/ryanlisse/engram/blob/HEAD/docs/research/letta-deep-dive.md"
  ]
}
```