Mastra core 1.76.0 adds durable run ownership and fencing

Mastra published @mastra/core 1.76.0 on GitHub on October 13, 2026. The release notes themselves are dated October 11, 2026. Mastra is an open-source TypeScript agent framework, and the main change in this release makes durable agent crash recovery safe across multiple instances: each run is now claimed by the execution driving it. The release also adds atomic working-memory merges on PostgreSQL and a new model: 'auto' default for Observational Memory.

Release facts

What changed

• Durable run ownership. The release notes say a run is claimed by the execution driving it: stream(), generate(), resume() or recover(). The claim lapses about 30 seconds after that process dies. recoverActiveRuns() skips runs that still have a live claim. recover() throws DURABLE_AGENT_RUN_ACTIVE unless you pass force: true. This fixes a bug where recovery re-ran runs that another process was still executing.
• Run fencing. If a storage adapter supports run fencing, it rejects writes from an execution that lost its run, so that execution can't overwrite messages, threads or workflow state. Mastra logs a warning when the store doesn't support fencing.
• Atomic working-memory merges on PostgreSQL. With scope: 'resource', partial updates are deep-merged inside a row-locked transaction. You can merge with mergeWorkingMemory() or with mode: "merge" over HTTP. If an adapter can't merge atomically, the server returns a 400 error instead of silently replacing the record.
• File handling. When a provider rejects an attached file, the new default UnsupportedFileHandler retries with the file removed or swapped for a sandbox path. FileUploadProcessor can upload user files into the workspace sandbox.
• Observational Memory auto model. The default is now model: 'auto' instead of google/gemini-2.5-flash. Explicit model IDs stay pinned.
• Observability. tracingOptions.nestUnderParent attaches a run as a child span under an earlier run. Trace queries gain matches / notMatches, and metrics add a usageId.

The notes also list breaking changes in @mastra/playground-ui. Old Metrics card views were removed, and MetricsCardGroup no longer accepts variant.

Questions

Will Observational Memory use a different model after upgrading? It may. The release notes say model: 'auto' may pick a different provider or model depending on which credentials are available. Setting an explicit model ID keeps it pinned.

Does every storage adapter get full crash-recovery protection? No, according to the notes. Run claims let recovery skip runs that are still live. But rejecting writes from an execution that lost ownership requires a storage adapter that supports run fencing.

Is Mastra open source? The Mastra site calls it an open-source TypeScript framework. However, the GitHub API reports no recognized license for the repository.

More context is on the Mastra tool hub and in the agent frameworks category. Related reading: the earlier Mastra Agent Controller launch and our OpenAI Agents alternatives comparison.