Why Microsoft Sentinel over Splunk¶

Status: Authored 2026-04-30 Audience: CISOs, CIOs, Security Architects, Federal Security Leadership Purpose: Executive brief for decision-makers evaluating a Splunk-to-Sentinel migration

Executive summary¶

The security information and event management (SIEM) market is at an inflection point. Cisco's $28 billion acquisition of Splunk, completed in March 2024, has fundamentally altered the competitive landscape. Splunk -- the dominant SIEM in federal and enterprise environments -- is now a product line within Cisco's broader security portfolio rather than an independent, SIEM-focused company.

Simultaneously, Microsoft has invested heavily in Sentinel as a cloud-native SIEM/SOAR platform with AI-native capabilities (Security Copilot), consumption-based pricing, and deep integration across the Microsoft security stack. For organizations already invested in Microsoft 365, Entra ID, and Defender XDR, Sentinel offers a unified security operations experience that Splunk cannot replicate without extensive add-ons and custom integrations.

This document presents the strategic case for migrating from Splunk to Microsoft Sentinel. It is written for decision-makers, not marketing audiences. Where Splunk retains advantages, we say so explicitly.

1. The Cisco acquisition changes the calculus¶

What happened¶

Cisco completed its acquisition of Splunk for $28 billion in March 2024. Splunk is now a wholly owned subsidiary of Cisco Systems, not an independent company.

What this means for Splunk customers¶

The risk of inaction¶

Staying on Splunk is itself a strategic decision with risk. Federal agencies that assume continuity may face:

• License cost escalation at next renewal (Cisco acquisition synergies often translate to price increases)
• Reduced innovation velocity as Splunk R&D competes with other Cisco priorities
• Talent attrition from Splunk engineering as post-acquisition integration progresses
• Integration friction if Cisco prioritizes Cisco-native security products over Splunk's open ecosystem

2. Cloud-native SIEM architecture¶

Splunk: infrastructure-heavy¶

Splunk Enterprise requires significant infrastructure to operate:

Splunk Enterprise Architecture:

    Heavy Forwarders ──> Indexer Cluster ──> Search Head Cluster
         │                    │                     │
    Deploy agents       Provision storage      Manage search
    Manage configs      Scale horizontally     Load balancing
    Network routing     Hot/Warm/Cold tiers    Knowledge objects
                        Replication factor
                        Bucket management

• Indexer clusters must be sized, provisioned, and maintained
• Search head clusters require load balancing and capacity planning
• Storage tiers (hot/warm/cold/frozen) must be managed manually
• Forwarder deployment at scale requires configuration management
• Upgrades are complex multi-component rolling operations
• High availability requires cluster replication configuration

Sentinel: cloud-native, zero infrastructure¶

Sentinel Architecture:

    Data Sources ──> Data Connectors ──> Log Analytics Workspace ──> Sentinel
                                              │                        │
                                         Auto-scales              Analytics Rules
                                         Auto-replicates          Playbooks
                                         Auto-indexes             Workbooks
                                         Managed by Azure         Threat Hunting
                                                                  Security Copilot

• No infrastructure to manage -- Azure handles all compute, storage, indexing
• Auto-scaling -- ingestion capacity scales with demand
• Built-in HA/DR -- Azure infrastructure provides zone and region redundancy
• Seamless updates -- new features deploy automatically, no upgrade windows
• Native multi-tenancy -- Azure Lighthouse for MSSP and multi-agency scenarios

What this means in practice¶

Bottom line: Sentinel eliminates the undifferentiated heavy lifting of SIEM infrastructure management. Your security team spends time on detection engineering and threat hunting, not indexer maintenance.

3. Security Copilot integration¶

Microsoft Security Copilot is the generative AI assistant built into the Microsoft security stack. Its integration with Sentinel is native and deep -- not a bolt-on.

What Security Copilot does in Sentinel¶

Splunk AI comparison¶

Splunk has introduced AI capabilities (Splunk AI Assistant, Splunk MLTK), but these are:

• Add-on products requiring separate licensing
• Not integrated into the core SIEM workflow the way Copilot is embedded in Sentinel
• Limited in scope -- Splunk AI Assistant focuses on SPL generation, not end-to-end incident triage
• Cisco's AI strategy post-acquisition may redirect AI investment to Cisco-branded products

Why this matters for federal¶

Federal SOC analysts face a talent shortage. The cybersecurity workforce gap in the US federal government exceeds 30,000 positions. Security Copilot acts as a force multiplier:

• Junior analysts can perform senior-level threat hunting with Copilot assistance
• KQL learning curve is reduced dramatically with natural-language query generation
• Incident triage time decreases when Copilot summarizes complex, multi-alert incidents
• Documentation burden is reduced with automated report generation

4. Consumption-based pricing vs volume licensing¶

Splunk pricing model¶

Splunk pricing is fundamentally volume-based:

• Splunk Enterprise: priced per GB of daily indexing volume (typically \(1,800-\)3,600 per GB/day annually)
• Splunk Cloud: similar volume-based pricing with platform fees
• Splunk Enterprise Security (ES): additional premium (often 50-100% of base license cost)
• Splunk SOAR: separate product with its own licensing
• Hidden costs: infrastructure (servers, storage, networking), admin FTE, app licensing

The structural problem: Security telemetry volumes grow 30-40% year-over-year. Splunk's volume-based model means costs escalate with data growth, creating a perverse incentive to reduce security visibility to control costs.

Sentinel pricing model¶

Sentinel pricing is consumption-based with significant cost optimizations:

• Pay-per-GB ingestion: no upfront licensing; pay only for data ingested
• Commitment tiers: discounts of 15-50% for committed daily ingestion volumes
• Free Microsoft data sources: Microsoft 365 audit logs, Entra ID sign-in logs, Defender XDR alerts, Azure Activity logs -- ingested at no cost
• Basic Logs tier: 60-75% cost reduction for high-volume, low-query data (e.g., verbose network flow logs)
• Archive tier: near-zero cost storage for compliance retention
• No separate SOAR licensing: Logic Apps (playbooks) are pay-per-execution
• No infrastructure costs: zero servers, zero storage management

Cost comparison at scale¶

For a federal SOC ingesting 50 TB/month:

See TCO Analysis for detailed modeling.

5. Unified Microsoft security stack¶

The integration advantage¶

Organizations using Microsoft 365, Entra ID, and Azure already have security telemetry flowing through Microsoft services. Sentinel is the natural aggregation point.

flowchart TD
    subgraph Microsoft["Microsoft Security Ecosystem"]
        M365[Microsoft 365]
        EID[Entra ID]
        DXDR[Defender XDR]
        DEP[Defender for Endpoint]
        DO365[Defender for Office 365]
        DCA[Defender for Cloud Apps]
        DCI[Defender for Cloud - Infrastructure]
        INTUNE[Intune]
    end

    subgraph Sentinel["Microsoft Sentinel"]
        SENT[Unified Incident Queue]
        ANALYTICS[Analytics Rules]
        COPILOT[Security Copilot]
    end

    M365 -->|Free ingestion| SENT
    EID -->|Free ingestion| SENT
    DXDR -->|Native integration| SENT
    DEP -->|Bi-directional| SENT
    DO365 -->|Auto-correlation| SENT
    DCA -->|UEBA signals| SENT
    DCI -->|Cloud alerts| SENT
    INTUNE -->|Device compliance| SENT

    SENT --> COPILOT

Key integrations that Splunk cannot replicate natively:

6. SIEM Migration Experience¶

Microsoft has built a purpose-built migration tool for Splunk customers.

What the SIEM Migration Experience provides¶

1. Upload SPL detection rules -- export your Splunk correlation searches and upload to the Defender portal
2. Copilot-powered translation -- each SPL rule is automatically translated to KQL with entity mapping
3. Translation status -- each rule is categorized as fully translated, partially translated, or not translated
4. Side-by-side review -- see SPL and KQL side by side for validation
5. Data connector recommendations -- the tool identifies which Sentinel data connectors you need
6. One-click deployment -- deploy validated analytics rules directly to your Sentinel workspace

Why this matters¶

The number-one barrier to SIEM migration is detection rule conversion. Organizations with 500+ Splunk correlation searches face months of manual SPL-to-KQL translation. The SIEM Migration Experience reduces this to days of review and validation rather than months of rewriting.

See Tutorial: SIEM Migration Experience for the step-by-step walkthrough.

7. Federal positioning¶

Splunk in federal today¶

Splunk holds dominant SIEM market share in the federal government:

• DoD: Splunk is the most widely deployed SIEM across military departments and combatant commands
• Intelligence Community: Splunk is used extensively for security analytics and operational intelligence
• Civilian agencies: Splunk is the incumbent SIEM at most large civilian agencies (DHS, DOJ, Treasury, State, HHS)
• CISA CDM: Splunk is used by many agencies for CDM dashboard integration

Sentinel in federal today¶

Sentinel's federal footprint is growing rapidly:

• Azure Government: Sentinel is available in Azure Government with FedRAMP High authorization
• IL4/IL5: Full support for IL4 workloads; IL5 support for most Sentinel capabilities
• DoD adoption: Multiple DoD components have migrated or are actively migrating to Sentinel
• ArcSight displacement: Sentinel is the primary beneficiary of ArcSight end-of-life migrations in federal
• CISA alignment: Microsoft's federal security team actively supports CDM integration with Sentinel

Compliance advantage¶

Note: For IL6 (classified SCI) workloads, Splunk retains an advantage. Sentinel does not currently operate at IL6. Organizations with IL6 requirements should plan a split architecture: Sentinel for IL4/IL5 unclassified SIEM, Splunk or alternative for IL6.

See Federal Migration Guide for comprehensive federal considerations.

8. Where Splunk retains advantages¶

This assessment is honest about where Splunk remains stronger today:

SPL maturity and ecosystem¶

SPL (Search Processing Language) has 20+ years of maturity. The Splunk ecosystem includes thousands of apps, add-ons, and community-contributed content on Splunkbase. While KQL is powerful and growing, SPL's ecosystem breadth is larger today.

On-premises deployment¶

Splunk Enterprise can be deployed entirely on-premises or in air-gapped environments. Sentinel is cloud-only. For organizations that require a fully on-premises SIEM (some classified environments, some OT/ICS networks), Splunk is the better fit.

Observability convergence¶

Splunk positions itself as a unified observability + security platform (logs, metrics, traces, and security events). While Microsoft offers Azure Monitor for observability and Sentinel for security, the integration between them -- though improving -- is not as seamless as Splunk's unified platform.

IL6 support¶

As noted above, Splunk operates at IL6 for classified workloads. Sentinel does not.

Existing tribal knowledge¶

Organizations with years of Splunk investment have institutional SPL knowledge, trained analysts, and battle-tested detection content. The switching cost is real and should not be underestimated.

9. Decision framework¶

Migrate to Sentinel when¶

• Your organization uses Microsoft 365, Entra ID, and/or Defender XDR
• Splunk license costs are a budget concern, especially with data growth
• You want to eliminate SIEM infrastructure management
• Security Copilot's AI capabilities align with your SOC modernization strategy
• You are already on Azure or Azure Government
• Your compliance requirements are IL5 or below
• You want consumption-based pricing that scales with workload, not fixed volume licensing

Stay on Splunk when¶

• You require IL6 support for classified workloads
• You need a fully on-premises or air-gapped SIEM
• Your organization has deep Splunk investment with minimal Microsoft footprint
• Unified observability (logs + metrics + traces + security) in a single platform is a hard requirement
• Your Splunk contract terms are favorable and long-term
• SOC analyst retraining cost outweighs license savings in your specific scenario

Split architecture¶

Many federal agencies will adopt a split approach:

• Sentinel for IL4/IL5 unclassified SIEM with Security Copilot and Microsoft stack integration
• Splunk (or ArcSight replacement) for IL6 classified SIEM where required
• CSA-in-a-Box as the analytics landing zone for security data from both environments

10. The CSA-in-a-Box advantage¶

The migration to Sentinel is not just a SIEM swap. With CSA-in-a-Box, security teams gain capabilities that neither Splunk nor Sentinel alone provides:

Summary¶

The case for Sentinel over Splunk is built on five pillars:

1. Cisco acquisition risk -- Splunk's future is uncertain under Cisco ownership
2. Cloud-native architecture -- eliminate infrastructure management burden
3. Security Copilot -- AI-native capabilities embedded in SIEM workflows
4. Consumption-based pricing -- structural cost advantage, especially with free Microsoft data sources
5. Unified Microsoft stack -- native integration with Defender XDR, Entra ID, M365

CSA-in-a-Box extends the value proposition by providing the analytics and governance platform that transforms Sentinel from a reactive SIEM into a proactive security intelligence platform.

Next steps:

• TCO Analysis -- model the cost savings for your specific environment
• Feature Mapping -- see how every Splunk feature maps to Sentinel
• Migration Playbook -- plan your migration
• Federal Guide -- federal-specific considerations

Maintainers: csa-inabox core team Last updated: 2026-04-30