PLATFORMS Signal 94
The best workflow engine is a programming language
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Vercel's Workflow SDK compiles TypeScript into durable workflows using 'use workflow' and 'use step' directives, eliminating DAG files and replacing Temporal's three interaction primitives with a single hook.
For engineers building long-running stateful logic, this removes the need to operate a separate workflow engine like Temporal, with its own server, worker fleet, and versioning complexity. The SDK promises a simpler developer experience by treating code as the DAG and using a single hook for human-in-the-loop interactions, but it requires adopting Vercel's execution environment and may not cover all Temporal features.
Written by elseif from the cluster below · every claim links back to a sourceThe three things worth knowing
Workflow SDK uses 'use workflow' and 'use step' directives to split TypeScript code into orchestrator and side-effecting steps, with the compiler generating the DAG from control flow.
It replaces Temporal's signals, queries, and updates with a single hook primitive, simplifying human-in-the-loop interactions.
The framework avoids the need to self-host Temporal's server and worker fleet, but versioning in-flight workflows still requires careful handling, as the patching API remains a multi-stage process.
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Vercel's Workflow SDK introduces a new approach to durable execution by treating the programming language itself as the workflow engine. Instead of defining a DAG explicitly, developers write normal TypeScript with 'use workflow' and 'use step' directives, and the compiler splits the code into bundles. This eliminates the need for a separate DAG file and makes the control flow the graph. The SDK also replaces Temporal's three interaction primitives, signals, queries, and updates, with a single hook, simplifying the mental model.
Adopting Workflow SDK means committing to Vercel's execution environment, as the author notes that to ship the desired experience, they needed to own the execution environment. This likely means deploying on Vercel's infrastructure, which may limit portability. Additionally, while the SDK removes the operational burden of running Temporal's server and worker fleet, it introduces its own runtime constraints. Developers must learn the new directive-based model and the hook primitive, which may not cover all use cases that Temporal's separate primitives handle.
The SDK's approach to versioning in-flight workflows still relies on a patching API similar to Temporal's, which can lead to code rot with many version flags. The article admits that evolving workflow code carefully is necessary, and over many changes, the workflow code becomes a thicket of version flags. Also, the hook primitive may not support all interaction patterns that signals, queries, and updates individually allow, such as blocking queries or buffered signals. The SDK is new and likely lacks the maturity and ecosystem of Temporal.
The article argues that a programming language is already a DAG, so workflow engines should leverage that. This is a philosophical shift from explicit graph definition to implicit control flow. For engineers, this means less boilerplate and a more natural way to write durable code. However, it also means trusting the compiler to correctly interpret directives and handle non-determinism, which is a critical concern in durable execution. The success of this approach depends on the robustness of the SDK's runtime and its ability to handle complex scenarios.
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