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AI · head to head

PromptLayer vs Seldon

PromptLayer logo

PromptLayer

AI

Collaboration platform for prompt management, evaluation, and observability

From
Free
Free plan
Yes
Full reviewWebsite
Seldon logo

Seldon

Machine Learning

Kubernetes model serving whose current version is licensed under the Business Source Licence

From
Free
Free plan
Yes
Full reviewWebsite

The short version

  • Each has a real cost: PromptLayer the free plan is capped at only 2,500 requests per month, quite limited for active production use.; Seldon seldon Core v2 is under the Business Source Licence rather than Apache 2.0, so production use requires a commercial agreement, and a team that evaluated it believing it was open source discovers the licence is the blocker exactly when the project is ready to ship.
  • They diverge on capability: PromptLayer covers Visual prompt management, Seldon covers Kubernetes custom resources.
  • Prices and features above were last checked on 30 August 2026.

Where they differ

Only the attributes on which PromptLayer and Seldon actually diverge.

Attributes where PromptLayer and Seldon differ
AttributePromptLayerSeldon
Platformsweb, apiLinux
CategoryAIMachine Learning
FoundedUnknown2014

Identical on both: starting price (Free), pricing model (freemium), free tier (Yes), user rating (Not yet rated).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in PromptLayer

  • Visual prompt management
  • Agent observability
  • Evaluations
  • Version control
  • Cost and latency monitoring
  • Agent workflow tracing

Only in Seldon

  • Kubernetes custom resources
  • Inference graphs
  • Traffic strategies
  • Open Inference Protocol
  • Alibi Explain
  • Alibi Detect
  • Kafka-backed pipelines in v2
  • Commercial control plane

What people use each for

The jobs each tool is most often brought in to do.

PromptLayer

  • Versioning and deploying prompts without code redeploysnot Seldon
  • Running evaluations with human review before production releasenot Seldon
  • Tracing multi-step agent workflows for debuggingnot Seldon
  • Monitoring LLM cost and latency by featurenot Seldon

Seldon

  • Serving an ensemble or a multi-stage inference path as one versioned deployment rather than as a chain of separate servicesnot PromptLayer
  • Running genuine production experiments where a share of live traffic goes to a candidate model and the results are comparednot PromptLayer
  • Regulated environments needing explanations and drift monitoring attached to the served model rather than bolted on laternot PromptLayer
  • Organisations with an established Kubernetes platform team who want serving expressed as manifests under existing deployment controlsnot PromptLayer

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

PromptLayer

  • The free plan is capped at only 2,500 requests per month, quite limited for active production use.
  • The Team plan jumps to $500/month, a large step up from the $49/month Pro plan.
  • Overage transaction fees apply on top of subscription costs, which can make total spend less predictable.
  • Enterprise-grade features like HIPAA BAAs and custom deployment require contacting sales.

Seldon

  • Seldon Core v2 is under the Business Source Licence rather than Apache 2.0, so production use requires a commercial agreement, and a team that evaluated it believing it was open source discovers the licence is the blocker exactly when the project is ready to ship.
  • Core v1 remains Apache 2.0 but is in maintenance, so taking the free route means running software that receives no new development while the architecture it belongs to moves on without it.
  • Version 2 is a different system rather than a newer release, with different custom resources, a scheduler component and a Kafka-based pipeline model, so migrating from v1 is a re-implementation of every deployment manifest rather than an upgrade.
  • Kafka is a dependency for v2 pipelines, so an organisation that does not already operate it takes on a distributed log with its own storage, retention, rebalancing and failure modes purely in order to serve models.
  • Everything assumes Kubernetes fluency and the failure modes are Kubernetes failure modes, custom resource version mismatches, an operator that will not reconcile, admission webhooks and resource limits terminating an inference pod mid-request, so it needs a platform engineer rather than a data scientist.

Pricing, plan by plan

PromptLayer

Free
  • FreeFree
    • 5 users
    • 2,500 requests/month
    • 1 workspace
  • Pro$49/month
    • Unlimited playgrounds and workspaces
    • 150MB datasets
    • Pay-as-you-go overage at $0.003/transaction
  • Team$500/month
    • 25 users
    • 100k+ monthly requests
    • Webhooks
  • Enterprise$undefined/mo
    • Custom limits
    • Role-based access controls
    • HIPAA with BAA

Seldon

Free
  • Seldon CoreFree
    • Open source
    • Kubernetes deployment
    • Model serving
  • Seldon DeployFree
    • Enterprise features
    • GUI
    • Monitoring

Which should you pick?

Choose PromptLayer if

  • You need visual prompt management.
  • You want to start without paying.
  • You work on web, api.
  • You also want agent observability.
PromptLayer review

Choose Seldon if

  • You need kubernetes custom resources.
  • You want to start without paying.
  • You work on Linux.
  • You also want inference graphs.
Seldon review

Questions people ask

Is PromptLayer or Seldon better?
Neither clearly leads. PromptLayer starts at Free and Seldon at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, PromptLayer or Seldon?
PromptLayer starts at Free and Seldon at Free.
Does PromptLayer or Seldon run on more platforms?
PromptLayer runs on web, api. Seldon runs on Linux.
Can I use PromptLayer for free?
Both have a free tier, so you can try either at no cost before committing.
What is PromptLayer best used for?
PromptLayer is most often used for versioning and deploying prompts without code redeploys, running evaluations with human review before production release, tracing multi-step agent workflows for debugging, monitoring llm cost and latency by feature. Of those, versioning and deploying prompts without code redeploys and running evaluations with human review before production release are not what Seldon is typically brought in for.
What can PromptLayer do that Seldon cannot?
PromptLayer covers Visual prompt management, Agent observability, Evaluations, Version control. Seldon covers Kubernetes custom resources, Inference graphs, Traffic strategies, Open Inference Protocol.

Answered from the vendors’ own pages

PromptLayer: What does PromptLayer cost?

PromptLayer has a free plan, a Pro plan at $49/month, a Team plan at $500/month, and custom Enterprise pricing, with additional usage billed per transaction beyond plan limits.

Source
Seldon: Is Seldon open source?

Partly, and this is the thing to check before you build on it. Core v1 is Apache 2.0 but in maintenance. Core v2 was moved to the Business Source Licence in 2024, which allows evaluation but not unlicensed production use. Verify the current licence of each component you intend to run, including MLServer and the Alibi libraries.

PromptLayer: Is there a free plan, and what are its limits?

The Free plan includes 5 users, 2,500 requests per month, 1 workspace, 250 monthly eval cell executions, and datasets up to 10MB.

Source
Seldon: What is the difference between v1 and v2?

Architecture, not just version number. v2 introduces a scheduler, a different set of custom resources and Kafka-backed pipelines. Manifests, mental model and operations all change, so treat a move as a project.

PromptLayer: How is usage metered beyond the plan limits?

Additional usage is charged per transaction for requests, agent runs, and evaluation cell runs, at $0.003/transaction on Pro and $0.002/transaction on Team.

Source
Seldon: Do I need Kubernetes?

Yes. It is a Kubernetes-native system and there is no meaningful deployment without a cluster and someone competent to run it.

Seldon: What is MLServer?

Seldon's Python inference server implementing the Open Inference Protocol, usable inside Seldon deployments or on its own. Check its current licence alongside Core's, since the company has moved projects onto the Business Source Licence.

Seldon: Do I have to run Kafka?

For v2 pipelines, yes. If you only need single models served, that dependency is a large amount of infrastructure for the benefit, and a simpler serving layer may be the better answer.

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