Do you need an LLM gateway, observability, or both?
An LLM gateway controls requests before they reach a provider. An observability tool records traces so you can inspect what happened. AcruxCore, MLflow’s gateway, and Helicone sit in the request path and act as a proxy. There they can route a call, cache it, check a budget, and hold the provider key. Langfuse, Phoenix, Opik, and Laminar collect traces without sitting in the request path, so they add no proxy.
Can you add and version the tools a model calls without deploying code?
In AcruxCore you define a tool once, keep every version of it, and the gateway runs it when the model calls it. So the tool the model sees and the code that ran are always the same version. You can add a tool, change it, or roll it back without deploying application code. No other platform in this comparison keeps versions of a tool and also runs it. Langfuse saves a tool schema in its playground, but does not version it or run it. Laminar stores tool schemas inside playground entries. Phoenix, Opik, and Helicone have no tool catalog. MLflow catalogs whole MCP servers rather than individual tools. In the MLflow workflow we tested, a single tool had no version history, and nothing ran the call.
Can you update prompts without deploying code?
Every platform here except Laminar has a prompt registry, so you can change a prompt without redeploying code. The registries differ in templating. AcruxCore and MLflow support Jinja2 conditionals and loops, so a prompt can branch on its inputs. Langfuse, Phoenix, Opik, and Helicone substitute variables only, and any branching logic stays in your application code. Laminar’s playground had no prompt versions, aliases, or variables.
What team structure and permissions do you need?
AcruxCore has members, invites, and roles inside a single team, with nothing above it, and one role per member. In the self-hosted versions we tested, Langfuse and Laminar had an organization or workspace layer above projects. Laminar had three workspace roles. Phoenix, Opik, and MLflow had no team, member, or invite management, and MLflow had no login screen. Helicone had one organization tier and no role field in its invite dialog.
Can you see who changed what and when, and does it cost extra?
Yes, in AcruxCore, and it costs nothing extra. Every prompt and every tool keeps its own change history. Owners and admins also see one audit trail for the whole team in the dashboard. That trail records 39 event types across eight areas: prompts, tools, members and invites, API keys, gateway credentials and budgets, secrets, evaluations, and trace settings. You can filter the trail by area, by one event type, or by person. Entries stay in the trail after the person who made them leaves the team, so you can still filter by that person. The trail is on by default, whether hosted or self-hosted, with nothing to pay and nothing to switch on. Of the other six platforms, Langfuse is the only one where we found an audit log, and that log needs the top paid plan even if you self-host. For Phoenix, Opik, Helicone, MLflow and Laminar we found no activity audit option in the platform.
How do you turn feedback into better prompts?
AcruxCore labels end-user feedback and developer notes separately, and both can be added to a dataset of test cases. Experiments run those cases against different prompt versions and models so you can compare the results. Automated rules score live traffic as it arrives. The optimizer uses a large language model to propose rewrites and tests them on the same cases as your production prompt. You can edit the prompt that instructs the optimizer, so the rewrites follow your own rules for a good prompt. Promoting a better rewrite creates a numbered version and moves the alias, so your app picks it up without a deployment. Opik and MLflow also have optimizers, with more algorithms than AcruxCore. Both run from the SDK only and cannot be started from the UI. Langfuse, Phoenix, and Helicone have no optimizer in the product, and Laminar has no stored prompt to optimize.
What does the license include?
Opik, Helicone, MLflow, Laminar, and AcruxCore are Apache 2.0, with no folder under a separate paid license. Langfuse has an MIT-licensed core and one folder under an enterprise license. Its audit log needs the top paid plan even if you self-host. Phoenix uses Elastic License 2.0, which is source-available rather than OSI-approved open source.