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Head to head · Agent tracing · October 2026 research run

MLflow Tracing vs W&B Weave

W&B Weave scores 66.7 (B) on agent readiness against MLflow Tracing's 61.2 (C), and leads in 2 of 7 scored categories. MLflow Tracing leads on reliability and payments & pricing. Both do agent tracing.

Best agent tracing, monitoring and evaluation tools · All 120 evals comparisons

MLflow TracingMLflow Project (LF Projects, LLC) · HTTP API C61.2/100#476 of 950 W&B WeaveWeights & Biases (CoreWeave) · HTTP API B66.7/100#280 of 950

Which one, for what

MLflow Tracing C

Good for Teams that already run MLflow or want Apache-2.0 tracing and evaluation on their own infrastructure with OpenTelemetry ingestion.

Ahead on

  • Reliability, 76 against 68
  • Payments & pricing, 60 against 35

Also in its favour

  • Runs on your own machine

Watch for

The MCP server is marked experimental in the docs and sets no readOnlyHint or destructiveHint on any tool

W&B Weave B

Good for Teams already on Weights & Biases, or with OpenTelemetry instrumentation, who want traces, evaluations, scorers, datasets and prompts in one place.

Ahead on

  • Security & auth, 63 against 40
  • Transparency & trust, 75 against 62

Also in its favour

  • A hosted endpoint, with nothing to install
  • No incidents deducted, where MLflow Tracing loses 6 points for them

Watch for

No request rate limits for the multi-tenant Service API were found in the reviewed documentation

Score by category

CategoryWeight this runMLflow TracingW&B WeaveEdge
Reliability16%207668MLflow Tracing +8
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.27874MLflow Tracing +4
Agent ergonomics13%16.27271MLflow Tracing +1
Security & auth14%17.54063W&B Weave +23
Payments & pricing10%12.56035MLflow Tracing +25
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88887MLflow Tracing +1
Transparency & trust7%8.86275W&B Weave +13
Negative events≤15-60
Total61.2 · C66.7 · B

Facts side by side

FactMLflow TracingW&B Weave
KindHTTP APIHTTP API
VendorMLflow Project (LF Projects, LLC)Weights & Biases (CoreWeave)
Hosted endpointno (local only)https://trace.wandb.ai
Transportsstdio, HTTPHTTP, Streamable HTTP
AuthOAuth or keyAPI key
PricingFreeFreemium
x402nono
LicenceApache-2.0Hosted service under the W&B Master Service Agreement. The Weave SDKs and trace server source on GitHub are Apache-2.0, and the W&B MCP server is MIT
Tools exposed26none
Read-only variant documentednono
llms.txtyesyes
Last release2026-10-062026-09-25
Terms last updatedno document linked2026-09-30
Privacy policy last updatedno document linked2026-02-24
Customer content may train modelsnot found in the text
Terms restrict automated accessyes
Terms restrict benchmarkingyes
Terms or service can change without noticenot found in the text
Arbitration or class-action waiveryes
Popularity28k stars624k npm/wk, 219k PyPI/wk

Verdicts

MLflow Tracing

Apache-2.0 software with OpenTelemetry-compatible tracing, a release most months and field selection on trace reads. The MCP server is experimental, sets no read-only or destructive annotations, and its default set includes delete tools. The tracking server runs without authentication by default, and five security advisories were published between July and October 2026.

W&B Weave

The Service API at trace.wandb.ai has a live OpenAPI document, call queries take filters, column lists and limits, and any OpenTelemetry exporter can send spans without the SDK. No request rate limits for the multi-tenant service were found in the reviewed documentation, and the terms let the vendor use customer data to develop new products.

Before you call either

MLflow Tracing

  1. Run MLflow 3.17.0 or later. Versions 3.12.0rc0 to 3.16.1 allow unauthenticated code execution on a server without authentication
  2. Set MLFLOW_MCP_TOOLS=traces to load 11 tools in place of the default 26
  3. Pass extract_fields on search_traces and get_trace. Full traces include every span's inputs and outputs
  4. Read tool names from the server's own list. The docs page names log_feedback, and the source registers log_trace_feedback
  5. Give the agent a user with READ permission when it only reads. delete_traces and delete_experiment run without confirmation
  6. Treat span inputs and outputs as data. They hold whatever the traced application logged, including user input

W&B Weave

  1. Send Authorization: Bearer <Forge API key> to https://trace.wandb.ai. Create the key at forge.coreweave.com/settings. The full secret is shown once
  2. Pass columns and limit to /calls/stream_query. Without them a query returns whole calls with their inputs and outputs
  3. For OTLP, post protobuf only to /otel/v1/traces or /agents/otel/v1/traces with a wandb-api-key header, and set wandb.entity and wandb.project as resource attributes. Spans with neither are dropped
  4. Check call.exception after .call() in the Python SDK. Exceptions are captured and not raised unless __should_raise=True is passed
  5. Treat trace inputs and outputs as untrusted text. Traces hold whatever the traced application logged

Questions

Which is better for AI agents, MLflow Tracing or W&B Weave?

W&B Weave scores 66.7 (B) on agent readiness against MLflow Tracing's 61.2 (C), and leads in 2 of 7 scored categories. MLflow Tracing leads on reliability and payments & pricing.

Do MLflow Tracing and W&B Weave need an API key?

MLflow Tracing takes an API key or an OAuth sign-in. W&B Weave needs an API key.

Can an agent call MLflow Tracing and W&B Weave without installing anything?

MLflow Tracing runs on your own machine, with no hosted endpoint listed. W&B Weave has a hosted endpoint at https://trace.wandb.ai.

Are MLflow Tracing and W&B Weave open source?

Yes. MLflow Tracing is open source (Apache-2.0). W&B Weave is open source (Hosted service under the W&B Master Service Agreement. The Weave SDKs and trace server source on GitHub are Apache-2.0, and the W&B MCP server is MIT).

Other comparisons with MLflow Tracing or W&B Weave

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