W&B Weave vs Langtrace
Both are observability & tracing tools. Here is how they actually differ on price, billing model and deployment.
W&B Weave
Weights & Biases' LLM tracing and evaluation product, now owned by CoreWeave after a reported $1.7B acquisition. Billed on GB of trace data ingested rather than spans or requests, which is a genuinely different cost model to everything else in the category.
Langtrace
An OpenTelemetry-native open-source tracing tool from Scale3 Labs. The cloud is still free because it has never been monetised - which is either a bargain or a runway risk depending on how you read a seed round raised around 2022. The AGPL-3.0 server license is the other thing to check before you commit.
| W&B Weave | Langtrace | |
|---|---|---|
| Category | Observability & Tracing | Observability & Tracing |
| Our rating | 4/5 | 3/5 |
| Starting price | Per-seat plus usage | Free (not yet monetised) |
| Billing meter | gb-ingested | No usage metering |
| Free plan | Yes | Yes |
| Free self-hosting | No or paid tier only | Yes, free |
| Best for | Teams already running Weights & Biases for model training and experiment tracking, who want LLM traces and evals in the same platform as their fine-tuning runs and are comfortable with usage-based ingestion billing. | Teams that want OpenTelemetry-native tracing with strong vector database visibility, are comfortable with AGPL on the server, and can tolerate the possibility of a pricing model appearing later. |
Our verdict on W&B Weave
W&B Weave is the strongest option in the category for one specific team - the one already on Weights & Biases. The lineage story is real and unmatched - a model fine-tuned in Sweeps and the eval run testing it appear in the same interface, which no AI-native competitor can offer because none of them do training. The instrumentation API is excellent, the custom scorers are plain Python, and the integration coverage is among the broadest available. Two things temper it. The billing metric is GB of trace data ingested, which is genuinely harder to forecast than per-span or per-seat pricing because it scales with prompt and context size, not just traffic. And CoreWeave now owns it following a reported $1.7B acquisition, which has come with interoperability pledges but leaves an open question about long-term direction. If you are not already a W&B customer, the bundled per-seat maths works against you and there are cheaper focused tools.
Full W&B Weave review →Our verdict on Langtrace
Langtrace is a well-built OpenTelemetry-native tracing tool with unusually good vector database instrumentation, and right now it costs nothing. Two things stop us rating it higher, and neither is about the product quality. The first is the license - the application is AGPL-3.0 while the SDKs are Apache 2.0, and that split matters. Instrumenting your app is safe; modifying the server and offering it as a service brings copyleft obligations most commercial teams will want legal review on. The second is commercial. The vendor states it is not currently charging for the cloud and will announce when it decides to monetise, and public funding data shows a roughly $5.3M seed raised around 2022. A free cloud with no revenue model and a four-year-old seed round is not a stable planning assumption. Use it, and self-host if it becomes load-bearing.
Full Langtrace review →Frequently Asked Questions
What is the main difference between W&B Weave and Langtrace?
W&B Weave: Teams already running Weights & Biases for model training and experiment tracking, who want LLM traces and evals in the same platform as their fine-tuning runs and are comfortable with usage-based ingestion billing. Langtrace: Teams that want OpenTelemetry-native tracing with strong vector database visibility, are comfortable with AGPL on the server, and can tolerate the possibility of a pricing model appearing later. Both sit in Observability & Tracing, so the decision usually comes down to billing model and deployment rather than raw capability.
Which is cheaper, W&B Weave or Langtrace?
It depends entirely on your workload shape, because they meter differently - W&B Weave bills on gb-ingested and Langtrace bills on no usage metering. Published starting prices are Per-seat plus usage and Free (not yet monetised) respectively, but those numbers are not comparable until you apply them to the same traffic. Use our cost calculator to model both against your own request volume and span count.
Can I self-host W&B Weave or Langtrace?
W&B Weave: No or paid tier only. Langtrace: Yes, free. Free self-hosting means no licence fee, not no cost - you still own the infrastructure, upgrades and on-call.