Open-Source SIEM in 2026: Free Software, Real Costs
"Free SIEM" is one of the most searched terms in security tooling. And open-source SIEM software is genuinely free to download and deploy. But the total cost of running it in production -- infrastructure, specialised staffing, maintenance, and detection rule development -- tells a more nuanced story. This guide provides honest cost analysis for every major open-source option.
The "Free" Reality Check
Open-source SIEM follows the "free software, expensive people" economic model. The software is genuinely free -- you can download Wazuh, ELK Stack, or Security Onion today and run a functional SIEM without paying a licensing fee. But production deployment requires servers (or cloud compute), storage, networking, and most importantly, engineers who understand how to deploy, configure, tune, and maintain these platforms.
The staffing reality is the critical variable. Elastic and Wazuh engineers command salary premiums of 20-40% over general systems administrators because the skillset is specialised and in demand. Finding, hiring, and retaining these engineers is often harder than budgeting for commercial SIEM licensing. In regions with tight cybersecurity labour markets, the time-to-hire for an Elastic engineer averages 3-6 months -- during which your open-source SIEM project stalls.
The honest bottom line: for a 50 GB/day deployment, open-source SIEM costs approximately $180,000-$280,000 per year in total (infrastructure + staffing + maintenance time). Microsoft Sentinel for the same volume costs $57,000-$95,000 in licensing with lower staffing requirements because the platform is managed. Splunk costs $108,000-$180,000 in licensing. Open-source is cheaper than Splunk and more expensive than Sentinel at this scale when staffing is included. At higher volumes (500+ GB/day), open-source becomes significantly cheaper because infrastructure scales linearly while per-GB licensing costs accelerate.
Open-Source SIEM Platforms Compared
Wazuh
License: GPLv2ELK Stack + Elastic Security
License: Elastic License / SSPLOpenSearch
License: Apache 2.0Security Onion
License: GPLv2Apache Metron (retired)
License: Apache 2.0When Open-Source Wins and When It Loses
Open-Source Wins When:
- • You already have Elastic/Wazuh expertise on staff
- • Existing ELK infrastructure can be extended for security
- • Very high data volume (500+ GB/day) makes per-GB licensing prohibitive
- • Unique data requirements need custom processing pipelines
- • Strong engineering culture that values control and customisation
- • Budget allows for specialist hiring but not commercial licensing
Open-Source Loses When:
- • No existing Elastic/Linux expertise on the team
- • Compliance audits require vendor-supported solutions
- • Time-to-value matters (compliance deadline, active threat)
- • Small team (1-2 people) without bandwidth for maintenance
- • Need for vendor support SLAs for critical security infrastructure
- • Total cost comparison favours Sentinel for your environment
The hybrid approach is increasingly popular: use Wazuh for endpoint monitoring and basic SIEM (free) alongside a commercial cloud SIEM like Sentinel for advanced analytics, compliance reporting, and managed infrastructure. This model captures the cost advantage of open-source for high-volume endpoint data while using commercial tooling for the complex correlation and compliance use cases where vendor support and pre-built content add the most value.
For organisations considering the commercial alternative to self-managed Elastic, see our Elastic Security pricing guide. For cost comparison across all vendor pricing models, see SIEM pricing models explained. For budget-constrained organisations of any size, our cost-by-size guide provides vendor recommendations per budget tier.
Open-Source SIEM FAQ
Is open-source SIEM really free?
Open-source SIEM software has zero licensing cost, but running it in production is far from free. The true annual cost includes infrastructure ($15,000-$50,000 for servers or cloud compute), specialised engineering staffing ($120,000-$180,000 per Elastic/Wazuh engineer due to the specialisation premium), ongoing maintenance consuming 20-30% of an engineer's time, custom detection rule development (no vendor-provided content packs), and the opportunity cost of slower time-to-value. For a 50 GB/day deployment, the total annual cost of open-source SIEM is typically $180,000-$280,000 -- cheaper than Splunk but often comparable to or more expensive than Microsoft Sentinel or managed SIEM services.
Which open-source SIEM is best in 2026?
Wazuh is the most popular open-source SIEM in 2026, offering built-in endpoint security, compliance dashboards, and an active community. The ELK Stack (Elasticsearch, Logstash, Kibana) with Elastic Security provides the most powerful search and analytics capabilities. OpenSearch (the AWS fork of Elasticsearch) offers a fully open-source alternative with growing security features. Security Onion bundles multiple tools into a network security monitoring platform. For pure SIEM use, Wazuh offers the best out-of-box experience; for advanced analytics and custom detection engineering, ELK with Elastic Security is more capable.
When does open-source SIEM save money vs commercial?
Open-source SIEM saves money versus commercial alternatives in three scenarios: (1) you already employ Elastic or Wazuh engineers and have existing ELK infrastructure, making the marginal cost of adding SIEM near-zero; (2) you have very high data volumes (500+ GB/day) where commercial per-GB licensing becomes extremely expensive but self-managed infrastructure scales more linearly; (3) you have unique data requirements that need custom processing pipelines not supported by commercial SIEM platforms. For organisations without existing expertise, the staffing investment typically erases the licensing savings.
How does Wazuh compare to Splunk on cost?
For a 50 GB/day deployment, Wazuh costs approximately $15,000-$30,000 per year in infrastructure (cloud or on-premise servers) versus Splunk at $108,000-$180,000 in licensing alone. However, Wazuh requires at least one dedicated engineer at $120,000-$180,000 per year for deployment, maintenance, rule development, and troubleshooting. Including this staffing cost, Wazuh totals $135,000-$210,000 versus Splunk at $238,000-$310,000 (licensing plus shared analyst time). The gap narrows further at smaller scales and widens at larger scales where infrastructure costs dominate over staffing.
Can I use open-source SIEM for compliance?
Open-source SIEM can meet many compliance requirements (log collection, retention, access controls, audit trails) but lacks the pre-built compliance reports, certified integrations, and vendor support SLAs that auditors expect. PCI-DSS, HIPAA, and SOX auditors are familiar with Splunk and Sentinel compliance modules; they may require additional documentation to accept Wazuh or ELK-based solutions. Wazuh includes built-in compliance dashboards for PCI-DSS, HIPAA, and GDPR that partially address this gap, but you may need to invest $20,000-$50,000 in custom report development and documentation to satisfy audit requirements.