# Langfuse

Aiolum story: https://aiolum.com/story/langfuse/ · added 2026-11-11 · updated 2026-11-11

**In short.** Langfuse (Open-source platform to trace, evaluate and monitor LLM applications, Germany): More than 2000 paying customers, January 2026. Evidence grade E: no revenue figure was checked. Team: 3 founders in 2022; 13 people at the sale in January 2026 (Startups Acquired, citing InfoWorld); 30 named on the company page in November 2026, after the sale to ClickHouse. Launched 19 July 2023; sold 30 months after launch.

Open-source platform to trace, evaluate and monitor LLM applications · Germany · AI-native · started small, grew after funding · sold · group: Developer tools and coding agents

- Outcome: More than 2000 paying customers, January 2026 (evidence grade of the headline number: E; no revenue figure)
- Launch: 19 July 2023; months from launch to the outcome: 30
- Team: 3 founders in 2022; 13 people at the sale in January 2026 (Startups Acquired, citing InfoWorld); 30 named on the company page in November 2026, after the sale to ClickHouse
- Outside funding: US$4M seed round announced by Langfuse on 7 November 2023; sold to ClickHouse in January 2026, price not disclosed
- Main factor: Own problem
- Meters, 1 to 4: evidence strength 1, copyable pattern 2, capital needed 2
- Tags: AI-native, Small team, Funded, Exit, B2B, Developer tools

Links:

- Visit langfuse.com: https://langfuse.com/

**The product.** A platform that records, scores and monitors the calls that an application makes to language models. Teams use it to find out why an answer was wrong and whether a change to a prompt helped. Developers can host it themselves for free, or pay for the hosted version, Langfuse Cloud.

**Why it worked.** The founders built it to fix a problem they had with their own LLM agents, and they released the code as open source. Langfuse said in November 2023 that they first built a test framework, then a tool for logging and debugging. Orrick, the law firm that advised the company, reported more than 2,000 paying customers in January 2026.

Evidence grades: A = disclosed by a public company, a filing or a payment processor, or verified by one; B = two or more independent reports agree, or a journalist confirmed it; C = a founder claim that no one else verified; D = reported, not verified: one founder claim or a third-party estimate with no second source; E = no revenue figure found, so the headline is a non-money fact and the other facts carry their own grades; calc = computed on this page from graded facts.

## Summary

Langfuse is an LLM observability platform. It records each call that a program makes to a large language model, so that engineers can debug the program. It stores a trace, which is the full record of one request through the application, and it scores the answers for quality.

Marc Klingen, Max Deichmann and Clemens Rawert started working together in 2022, according to the company handbook. Their first product was a usage-based billing tool named Finto, and they switched to LLM tools during Y Combinator's winter 2023 batch. Clemens Rawert wrote in the launch changelog that Langfuse launched on 19 July 2023 after two months of work. Langfuse announced a US$4M seed round on 7 November 2023, and ClickHouse announced the acquisition on 16 January 2026.

The headline is a count, not a money figure. Orrick wrote in January 2026 that Langfuse had more than 2,000 paying customers. No source read gives revenue or the price of the sale. Startups Acquired, a deal tracker, reports a team of 13 at the sale and cites InfoWorld for it.

## Why did Langfuse work?

### The founders built it to fix their own agent problems

In the founders' words, they were building agents themselves and kept meeting the same problems. Going from a demo to a product that runs in production was hard. They tested the first version with other founders from their Y Combinator batch, then released it as open source.

### Engineers in enterprises hosted the open-source version themselves

Langfuse said in November 2023 that it had hit a nerve with individual contributors in enterprises who host Langfuse to keep control of production data. Langfuse Cloud is the hosted version, with a free plan and paid plans. Orrick reported more than 2,000 paying customers by January 2026.

### A move to ClickHouse let it serve large customers

The founders wrote that the first version ran as one container with a Postgres database, and that Postgres became slow for the largest customers. Version 3 moved the trace data to ClickHouse. ClickHouse later became the buyer.

## How it was built

These details come from the founders' own posts. They are grade C.

- The first version was written on Next.js, Vercel and Postgres, and ran as a single container with one Postgres database.
- By summer 2023 traffic spikes pushed response times of the ingestion API up to 50 seconds, according to the founders.
- Version 3 sends all ingestion traffic through a queue in Redis, keeps events in S3, and writes traces to ClickHouse.
- The founders traced Langfuse itself with Datadog while they compared Postgres and ClickHouse read times.
- All SDKs, integrations and the application are open source, and the founders describe them as simple to self-host.

Sources: [9, 2]

## Who tried this before Langfuse, and why did they fail?

Three developer-tool startups in our database of failed startups sold to engineers and then closed. The values below are from that database on 11 November 2026 and are not independently verified.

The failed startups come from our database of dead startups, retold here in our own words; Its entries are AI-assisted summaries of public sources, so they carry no evidence grade.

### CodeSee (2020 to 2024; funding US$10.0M burned; cause: Free users did not become paying customers)

- Promise: Automatic visual maps of a codebase, so developers understand it faster.
- Why it died: The record says it had traction with open-source projects and some enterprise pilots. It struggled to convert free users to paid customers and shut down in 2024.
- Record: 

### Testmunk (2012 to 2015; funding US$120K burned; cause: Competition)

- Promise: Automated testing of mobile apps on real devices.
- Why it died: The record attributes the failure to a market that filled up with automated testing platforms. It names BrowserStack as a competitor and says a device farm was costly to run.
- Record: 

### Nitrous.io (2012 to 2016; funding US$8.0M burned; cause: Competition and timing)

- Promise: A cloud development environment that removes the setup of a developer's local machine.
- Why it died: The record calls the cause "right idea, wrong timing, fatal competition" and says larger platforms later won this market.
- Record: 

## What changed

Each of the three sold tools to engineers and met either larger platforms or a free alternative. CodeSee did not turn free users into paying ones. Testmunk and Nitrous.io were pushed out by bigger competitors, according to the database.

Langfuse gave its code away under an open-source licence and charged for hosting and enterprise features. It also used ClickHouse for its data layer, and ClickHouse became the buyer. The sources do not say whether this caused the sale.

## Can one person copy Langfuse now?

**Verdict: Partly. The open-source start can be copied, but the sale cannot be planned.**

Three founders with engineering skill built a tool for a problem they had, and released it for free. The founders say the sale was not planned. A new team can copy the sequence, and it needs funding to reach enterprise scale.

1. Build the tool for a problem you meet in your own AI projects.
2. Release the code under an open-source licence and let engineers self-host it.
3. Sell a hosted version for teams that do not want to run it.
4. Move the data layer to a database that fits the load before the largest customers leave.

**What is still open.** Other tools that engineers need when AI applications reach production: cost tracking, test sets, prompt review, and access control.

## How much did Langfuse make, and what was it sold for? The numbers, graded

A funded open-source company that was sold with no price and no revenue figure. The facts below are mostly statements by the company, its law firm and its buyer

| Fact | Value | Grade | Note | Sources |
|---|---|---|---|---|
| Company start | 2022, by three founders | C | Company handbook: "We got started working together in 2022", first on a usage-based billing product named Finto. Orrick wrote on 26 January 2026 that Langfuse was "founded in 2023". The company page names Marc Klingen, Max Deichmann and Clemens Rawert as co-founders. | [12, 4, 6] |
| Launch | 19 July 2023 | C | Launch changelog, signed by Clemens Rawert: "After working on the initial version for 2 months, we are excited to launch Langfuse today!" That is 30 months before the January 2026 sale. | [8] |
| Seed round | US$4M, announced 7 November 2023 | C | Langfuse's own announcement names Lightspeed Venture Partners, La Famiglia and Y Combinator. Orrick lists Y Combinator, Lightspeed and General Catalyst as earlier investors, so the two lists differ. | [2, 4] |
| Sale to ClickHouse | announced 16 January 2026 | A | ClickHouse announced the acquisition in its press release of 16 January 2026. The release names no price. Langfuse's founders wrote that the whole team joins ClickHouse. | [3, 1] |
| Sale price | not disclosed | D | Startups Acquired: "Neither side disclosed the price or how it was paid." The ClickHouse release and the Langfuse post give no price. | [5, 3, 1] |
| Paying customers, January 2026 | more than 2,000 | C | Orrick's release, 26 January 2026. Orrick advised Langfuse, so this is a statement by the seller's side. It is a count, not revenue. | [4] |
| Team at the sale | 13 people | D | Startups Acquired reports that InfoWorld wrote this. The InfoWorld article could not be read, so the number rests on one retelling. | [5] |
| Team on the company page, November 2026 | 30 named people | C | The company page lists 30 names with roles, ten months after the sale. Three are co-founders. This is the team inside ClickHouse, not the team at the sale. | [6] |
| Open-source use, end of 2025 | 20,470 GitHub stars, 26M+ SDK installs a month, 6M+ Docker pulls | C | ClickHouse's description of Langfuse in its January 2026 release. These are the buyer's counters and no source checks them. | [3] |
| Plan to sell | none, with Series A term sheets in hand | C | The founders wrote in the post that announced the sale: "We didn't plan to sell the company. Actually, we had Term Sheets for a great Series A". | [1] |
| Prices, November 2026 | US$29, US$199 and US$2,499 a month | C | Core, Pro and Enterprise on the pricing page read on 11 November 2026, after the sale. The company handbook dates the Core price of US$29 to September 2025. | [7, 12] |
| Link to the buyer before the sale | Langfuse Cloud is a large customer of ClickHouse Cloud | C | The founders' post of January 2026. The product moved from Postgres to ClickHouse with its version 3. | [1, 9] |

How to read this table. Grade A is a disclosure by the buyer. Grade C is a statement by the company or by a firm that spoke for it. Grade D is a report that rests on one unchecked retelling.

## Pricing

Langfuse Cloud prices on the company's pricing page, read on 11 November 2026, ten months after the sale (grade C)

| Plan | Per month, billed yearly (US$) | Per month, billed monthly (US$) | Limit |
|---|---|---|---|
| Hobby |  | 0 | 50,000 units a month, 30 days of data, 2 users |
| Core |  | 29 | 100,000 units a month, 90 days of data, unlimited users |
| Pro |  | 199 | 100,000 units a month, 3 years of data, high rate limits |
| Enterprise |  | 2,499 | Pro plus Teams, audit logs, uptime and support SLAs |

The Hobby plan is free. Core, Pro and Enterprise each include 100,000 units a month, and the page lists US$8 for each further 100,000 units. The page shows monthly prices only. The Teams add-on at US$300 a month is optional with Pro. The site now belongs to ClickHouse, and no copy of the page from before the sale could be read. The company handbook says the Core price fell from US$59 to US$29 a month in September 2025, before the sale.

## When did Langfuse launch, and how did it grow? Timeline

From a first product in 2022 to a sale in January 2026, 30 months after the Langfuse launch. Each entry carries its grade.

- **2022 to early 2023** (grade C [12, 2, 6]): The three founders start with a billing product named Finto. They enter Y Combinator's winter 2023 batch in San Francisco and build several LLM applications.
- **19 July 2023** (grade C [8, 2]): Launch after two months of work on the first version. The code is open source.
- **August 2023** (grade C [2]): Langfuse becomes product of the day when it launches on Product Hunt.
- **7 November 2023** (grade C [2]): Langfuse announces a US$4M seed round.
- **16 January 2026** (grade A [3, 1]): ClickHouse announces the acquisition on the day of its US$400M Series D announcement. The whole Langfuse team joins ClickHouse.
- **26 January 2026** (grade C [4]): Orrick publishes its release and reports more than 2,000 paying customers.

## What could go wrong for Langfuse?

- **What is not verified.** No revenue figure and no sale price was found. The count of more than 2,000 paying customers comes from Orrick, the law firm of Langfuse. The team of 13 comes from Startups Acquired, which cites InfoWorld. Orrick gives 2023 as the founding year, and the company handbook says the founders started in 2022 with another product. A reader could look for the InfoWorld article, a ClickHouse filing or an interview with a founder.
- **Counters, logo rows and badges are company claims.** The home page in November 2026 says Langfuse is used by 21 of the Fortune 50, by 50,000+ companies and has 35,000+ GitHub stars. The pricing page shows "Trusted by" logo rows. The home page lists SOC 2 Type II, ISO 27001, FIPS 140-3, GDPR and a HIPAA-ready region, and it shows 65M+ SDK installs a month. ClickHouse said 19 of the Fortune 50 and 20,470 stars in January 2026. Orrick's text says ">2,000 GitHub stars". No source read confirms these.
- **The pages now belong to the buyer.** The site footer reads "2022–2026 ClickHouse, Inc.". The prices, counters and team list on it describe Langfuse after the sale, not at the sale. The Internet Archive refused automated access, so no earlier copy was read.
- **The team grew after the seed round.** Three founders started the company in 2022, and the first two engineers joined in February 2024, according to the company handbook. Startups Acquired reports 13 people at the sale. The company page lists 30 named people in November 2026, ten months after ClickHouse bought the company. That number is the team inside ClickHouse, not the team that built the business.

## Sources

1. Langfuse blog: Langfuse joins ClickHouse, January 2026 — https://langfuse.com/blog/joining-clickhouse (grade C). Read in full. The founders' account of the sale, the move to ClickHouse and the Series A term sheets.
2. Langfuse blog, 7 November 2023: Langfuse raises $4M — https://langfuse.com/blog/announcing-our-seed-round (grade C). Read in full. Source for the seed round, the Product Hunt launch and the open-source release.
3. ClickHouse press release, 16 January 2026: ClickHouse raises $400 million Series D, acquires Langfuse, launches Postgres — https://clickhouse.com/blog/clickhouse-raises-400-million-series-d-acquires-langfuse-launches-postgres (grade A). Read in full. The buyer's announcement of the acquisition and its counters for Langfuse.
4. Orrick, 26 January 2026: Open-source LLM Observability: Langfuse Acquired by ClickHouse, Inc. — https://www.orrick.com/en/News/2026/01/Open-source-LLM-Observability-Langfuse-Acquired-by-ClickHouse-Inc (grade C). Read in full. The law firm's release. Source for the founding year, the founders and the paying-customer count.
5. Startups Acquired: ClickHouse acquires Langfuse, the open-source LLM observability platform — https://www.startupsacquired.com/deals/clickhouse-acquires-langfuse (grade D). Read in full. A deal tracker. Source for the team of 13 (citing InfoWorld, not read) and for the undisclosed price.
6. Langfuse company page, read 11 November 2026 — https://langfuse.com/about (grade C). Read in full. Source for the co-founders, the Y Combinator batch and the list of 30 named people.
7. Langfuse pricing page, read 11 November 2026 — https://langfuse.com/pricing (grade C). Read in full. Source for the plans and prices, which are those of the time after the sale.
8. Langfuse changelog, 19 July 2023: Launch — https://langfuse.com/changelog/2023-07-19-launch (grade C). Read in full. Signed by Clemens Rawert. Source for the launch date and the two months of work.
9. Langfuse blog: Langfuse v3 infrastructure evolution — https://langfuse.com/blog/2024-12-langfuse-v3-infrastructure-evolution (grade C). Read in full. The founders' account of the first stack and the move from Postgres to ClickHouse.
10. Langfuse home page, read 11 November 2026 — https://langfuse.com/ (grade C). Read in full. Source for the counters, badges and the self-hosting offer.
11. Database of failed startups, local export — /method/#dead (grade C). Record pages read on the website on the day of writing. AI-written summaries, not independently verified. Source for the failed predecessors.
12. Langfuse handbook: How did we get here?, read 11 November 2026 — https://langfuse.com/handbook/chapters/story (grade C). Read in full. The company's own timeline. Source for the 2022 start with the billing product Finto and the first engineers in February 2024. Also the source for the Core price change of September 2025.

Contact: aiolum@livyden.com. Run Langfuse? Send corrections or a verified figure to aiolum@livyden.com (subject: Correction: Langfuse).