Letta changelog: what's new each month
Every stable Letta release summarised by month: the highlights, new features, improvements, fixes and anything you need to act on. 3 months covered; the current month updates daily.
May 2026
1 release: 0.16.8
May brought security improvements and bug fixes to Letta. The month focused on stability and safer data handling between components.
Highlights
- Security fix: tool results now use JSON instead of pickle for safer data transport between sandbox and server
Fixed
- Workflows update fix
March 2026
2 releases: 0.16.6 → 0.16.7
March brought major improvements to conversation management and memory handling in Letta. The release focused on fixing edge cases in system message initialization, removing outdated block limits, and substantially improving the compaction and summarization pipeline.
- Block limit validation has been removed; blocks no longer have size restrictions.
Highlights
- Conversations now support agent-direct mode with conversationid="default", simplifying the API for direct agent interactions.
- Global context window default increased from 32k to 128k tokens for better out-of-the-box performance.
- Block limits have been removed, allowing memory blocks to grow freely without artificial constraints.
- System messages are now compiled and persisted when conversations are created, eliminating timing edge cases.
- Compaction and summarization pipeline significantly improved to handle overflow, preserve models correctly, and maintain structured content during memory summarization.
New
- Support for conversationid="default" combined with agentid across all conversation endpoints.
- Lock-key handling in agent-direct flows to prevent concurrent execution conflicts.
- Immediate system message compilation and persistence at conversation creation time.
Improved
- Context window is now preserved when overriding conversation models, fixing fallback to 32k behavior.
- Summarizer prompt enhanced to retain plan files, GitHub PRs, and other structured content during memory compaction.
- Error messages for context window exceeded conditions now provide descriptive information.
- System prompt size warnings are displayed during compaction operations.
- Compaction model selection no longer leaves old summarizer models behind when agent model is changed.
- Global context window default raised from 32k to 128k tokens for self-hosted servers with unknown models.
Fixed
- Fixed modelsettings.maxoutputtokens default behavior to avoid silently overriding existing maxtokens unless explicitly set.
- Fixed double-compaction and runaway compaction loops in the overflow handling.
- Fixed bug where non-default conversations fell back to 32k context window on model override.
- Fixed BYOK summarization provider fallback that was incorrectly firing for BYOK requests.
February 2026
1 release: 0.16.5
February brought a maintenance release to Letta with version updates.
Summaries are written automatically from the official release notes (full changelog ↗); check the original notes before relying on a detail. Letta: pricing, features and alternatives · All changelogs