AI SDK WorkflowAgent: prepareStep overrides now last one step, and tools no longer see the system prompt (November 13, 2026)

What changed

On November 13, 2026 Vercel published @ai-sdk/workflow 2.0.104 and 2.0.105. Both are patch releases, but they change how WorkflowAgent behaves.

In 2.0.104:

• model, toolChoice, activeTools and generation settings returned from prepareStep now apply only to the current step. Before, they carried into all later steps.
• Tools and tool callbacks no longer receive the system prompt or the assistant message holding the current tool call in messages.
• onError and onAbort can be set in the constructor, like ToolLoopAgent. Constructor callbacks run first.
• stream() adds up totalUsage like ToolLoopAgent, and counts the provider did not report stay undefined instead of 0.

In 2.0.105:

• An abort during a model step now calls onAbort instead of onError.
• Instructions, provider options and headers from prepareStep now behave as they do in ToolLoopAgent.
• An async generator tool's result is the last value it yields. A generator that throws after yielding gives a tool error.
• New options: toolApproval (overrides needsApproval; denied calls get an execution-denied result), toolOrder, experimental_refineToolInput, and a timeout object with totalMs, stepMs, firstChunkMs and chunkMs. Invalid timeout values throw InvalidArgumentError.
• Provider warnings from every model call go through the AI SDK warning logger, controlled by AI_SDK_LOG_WARNINGS.

Prerequisites

• An app that uses WorkflowAgent from @ai-sdk/workflow

Steps

1. If your prepareStep returns a model, , or settings and you relied on them staying in force, return them on every step where you need them.