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@mastra/client-js

What changed in @mastra/client-js 1, from its official release notes, upgrade guides and advisories. Sources checked 2026-10-19.

3 breaking1 deprecations19 new APIs and options4 fixes and other

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@unstale/cli on npm

@mastra/client-js 127 changes

Breaking changes 3

  • Supports mode: 'merge' for atomic working-memory merges; requests are rejected with HTTP 400 when the storage adapter does not support atomic merges.

    1.53.0release notes

  • Requests conflicting with a run's state now return 409 Conflict instead of 500.

    1.53.0release notes

  • With reconnect enabled, resubscribe failures with 4xx or 501 errors now reject with the original error instead of retrying; other documented retry cases remain.

    1.53.0release notes

Deprecations 1

  • experimentIdA and experimentIdB still support two-experiment comparisons but are deprecated in favor of experimentIds.

    1.54.0release notes

New APIs and options 19

  • Adds a method for queuing a typed signal behind the active thread run.

    1.55.0release notes

  • Adds client-side trace aggregation by time range, grouping, and measures; check capabilities.traceAggregate before calling it.

    1.55.0release notes

  • Adds errorPreview to trace list rows and querySpans() rows.

    1.55.0release notes

  • Adds errorTruncated to querySpans() rows.

    1.55.0release notes

  • Adds outputPreview to trace list rows.

    1.55.0release notes

  • Adds an optional observability capability indicating how long traces are kept, so clients can avoid offering dates whose traces are gone.

    1.55.0release notes

  • An exported type describes the output stored for agent experiment targets, including preserved error details.

    1.54.0release notes

  • Compare two to ten experiments at once against a baseline by passing experimentIds and optionally baselineId.

    1.54.0release notes

  • An exported type describes experiment result output by target.

    1.54.0release notes

  • The /steer and /follow-up routes accept the files field and limits already supported by /messages.

    1.54.0release notes

  • AgentController followUp accepts file attachments, including when the message is queued behind an active run.

    1.54.0release notes

  • Generated Agent Controller tool-suspension route types now include an optional run id field.

    1.54.0release notes

  • An exported type describes the output stored for scorer experiment targets.

    1.54.0release notes

  • AgentController steer accepts file attachments, including when the message is queued behind an active run.

    1.54.0release notes

  • Experiment results include targetType, which lets TypeScript narrow output to typed agent or scorer results; workflow, processor, and caller-driven outputs remain unknown.

    1.54.0release notes

  • Gets an experiment by ID without requiring its dataset.

    1.53.0release notes

  • Added as a trace-query operator in the generated trace-query types.

    1.53.0release notes

  • Added as a trace-query operator in the generated trace-query types.

    1.53.0release notes

  • The Client SDK recognizes this live session event, allowing web clients to respond immediately to the agent's task-completion verdict.

    1.53.0release notes

Fixes and other changes 4

  • Failed agent runs now store error.message and error.stack instead of an empty object.

    1.54.0release notes

  • Session streams send the current display state as their first event; merge currentMessage by message ID rather than appending it.

    1.53.0release notes

  • nestUnderParent is no longer dropped from agent and workflow requests sent over HTTP, preserving the run's parent-child trace relationship.

    1.53.0release notes

  • Forwards options, including speaker, to the voice provider; options.speaker takes precedence over the top-level speakerId when both are sent.

    1.53.0release notes