| Sumn | Temporal | |
|---|---|---|
| What you're buying | Isolated stages, run budgets, judged and held gates, an attention inbox and a per-run record, supplied together and enforced by the runner rather than asked for in a prompt. | A durable runtime, mature SDKs, and first-party integrations that make agent calls durable. The layer above them, where the bounds and the checks live, is yours to write. |
| Best fit | Unattended agent processes, where model work needs bounds, checks, and somewhere for a person to step in. | Durable workflows of any kind. Payments, provisioning, order fulfilment, long-running service coordination. Agent work is one use among many. |
| Durability | Runs checkpoint at stage boundaries and resume from the last completed one after a crash or deploy. Inside a stage, finished turns are recorded (what the model said, the tools it called, what came back) and replayed into the new attempt rather than run again. | Event-sourced workflow history with replay after a worker failure, and years of production hardening behind it.Both keep your progress, at different units. Temporal's is finer, because it replays the workflow code itself where a stage boundary is the smallest thing a Sumn run resumes from. In practice a crash costs you the model call that was in flight, not the ones before it. |
| Agent workloads | Every stage runs in a fresh isolated VM with its own kernel, destroyed after, so its files and processes never reach the next stage. Model routing and output contracts are part of the platform. | Model calls run as activities, and their agent SDK integrations make those calls durable and retryable. Per-stage workload isolation, model routing, key handling and output contracts sit outside all of that, so that layer is yours to build and keep patched. |
| Spend control | A budget per run and per playbook, enforced mid-run. At the cap the playbook does what it declared: stop, or pause warm holding its work and send the decision to the inbox. Nothing inside the run can raise the ceiling. | Temporal Cloud meters and bills its own usage. What a run spends on model calls sits outside the engine, so a cap that halts one mid-flight is code you write and test. |
| Human oversight | Gates are first-class: judged gates apply criteria you wrote, held gates wait for a person. Both land in one attention inbox, so someone clears the exceptions instead of reading every run. | A workflow can wait on a person through signals or updates. The reviewer's screen, the routing rules and the queue are an app your team builds and runs. |
| Who can own a process | A process owner can change a playbook once its systems are connected, without waiting on an engineer to ship a code change. New integrations and new checks still need one. | Workflow definitions are application code, so an engineer implements and maintains them even when someone else owns the process. |
| Multi-model | Bring your own keys. Anthropic, OpenAI, Google and any OpenAI-compatible endpoint sit in one playbook, with per-call cost on the receipt. | Each provider is a client library called from an activity, with Temporal's retry, timeout and history wrapped around the call. Routing, fallback, key isolation and cost attribution are yours. |
| Keeping the pieces in step | One runner holds the budget, the gates, the record and the queue, so the ceiling knows what the retry already spent and the gate sees the run that produced the work. | Durable coordination for whatever you build on it. The budget, the gates, the record and the queue still have to know what each other did, and keeping them in step is your application's job. |
| Who operates it | Hosted. Sumn runs the infrastructure, including the isolated VM each stage gets. | Your choice. Run the server yourself on your own hardware, or take Temporal Cloud and skip operating it.If running the orchestrator yourself is a requirement rather than a preference, Temporal is the one that offers it. |
| What your team has to implement | Define the stages, connect the systems they touch, then set the budgets and gates. | Implement the workflow and its activities, then build whichever isolation, spend enforcement, approval surface and record the process needs, and operate them for as long as it runs. |
Where Temporal is strong
- It's MIT-licensed and self-hostable. You can run the server on your own hardware with no vendor between you and your workflows, or take Temporal Cloud and skip operating it.
- A mature runtime for long-lived workflows, with event history, retries, timers, signals and child workflows, hardened over years of production use.
- Workflow logic stays in code, in SDKs your backend engineers may already know, across the major languages.
Pick Temporal when the job is durable application workflows and you want that logic in code, especially where it already runs services you depend on. The two also coexist without much friction: service orchestration stays in Temporal, and the processes someone currently babysits by hand move to Sumn playbooks. Pick Sumn when the job is specifically unattended agent processes, and you want the isolation, the spend ceiling, the gates and the queue a person clears already enforced on every run.
Is Sumn built on Temporal?
No, and we looked at it seriously when we were building. Sumn runs its own durable execution layer, checkpointing completed stages and resuming from the last one after a crash or deploy. Temporal persists workflow history and replays the workflow code. Both keep your progress; they do it at different units.
What happens if a stage dies part-way through?
The run resumes from the last completed stage, and the finished turns inside the dead stage are replayed into the new attempt from the record rather than run again. The model call that was in flight when it died is the part you pay for twice. Tool calls that change something outside the run need to be safe to repeat, the same as they would anywhere else.
Can Sumn and Temporal coexist?
Yes. Keep code-first service workflows in Temporal, and use Sumn for agent processes that need isolated execution, a model-spend cap, enforced gates or a queue a person clears.
Do I need engineers to write a playbook?
Someone has to describe the process precisely, and someone has to connect the systems it touches and write the checks. Once those exist, a playbook is versioned data a process owner can change without touching workflow code.
We already run Temporal. Is Sumn redundant?
It can be. If your Temporal stack already gives agent runs isolated execution, an enforced spend cap, gates and a queue people actually clear, compare that setup with Sumn directly. If those are still separate projects, count what it takes to keep them running.
See how Sumn runs a playbook →The homepage has a live run you can watch. No signup.