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The harness is a separate package. Import its runtime, drivers, definitions, abilities, and policies from @agentium/harness. Continue importing Agent, Team, Workflow, providers, and the neutral execution contracts from @agentium/core.
These removals apply in Agentium 4.0.0. Upgrade core and harness together and follow the full v4 migration guide for other integrations.

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Replace removed entrypoints

The package quickstart shows the complete replacement. A minimal migration keeps your Agent configuration, wraps it with agentDriver(config), and starts it through runtime.run(input, { identity, sessionId }).

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Decide ownership during migration

Passing an existing Agent borrows it. Passing configuration creates a run-owned Agent and applies definition defaults/limits. If your old setup relied on implicit defaults, enumerate workspace access, context files, skills, filesystem, subagents, file memory, and session search before enabling them. Move execution permissions to grants, run-wide limits to budgets, and step selection to a controller. Keep host authentication outside the harness. Do not assume an old transcript contains enough information to resume a partially executed run; legacy imports are marked non-replayable. The old /agents/harness and /api-reference/harness URLs redirect to the package overview and complete reference. They no longer identify separate Agent features. Next: definitions, runtime configuration, or API reference.