Microsoft Sentinel vs Splunk vs Sophos Fusion: $2M SIEM Gap [2026]

Sophos pulled the trigger on August 15, 2026, taking its rebuilt Next-Gen SIEM, an expanded Managed Detection and Response service, and a re-engineered XDR platform to general availability under one umbrella called Sophos Fusion. The launch lands at an awkward moment for the two SIEM incumbents most security teams already budget around: Microsoft Sentinel, which just added new Security Compute Unit charges for its entity analyzer feature, and Splunk Enterprise Security, now two years into life under Cisco ownership and still shifting its pricing model. For a SOC lead staring down a renewal, the question isn’t academic. It’s whether to keep paying per gigabyte, switch to a workload-based model, or bet on a platform that charges by user and server instead.

This comparison breaks down Microsoft Sentinel vs Splunk vs Sophos Fusion on the numbers that actually move a security budget: ingestion pricing, retention limits, integration counts, deployment architecture, and where each platform tends to win or lose in a real SOC. We pulled current pricing from Microsoft’s own Azure documentation, Splunk’s published pricing FAQ, and Sophos’s Fusion launch materials, along with third-party pricing benchmarks from CostBench and Expanso. The goal is a clear-eyed verdict, not a vendor pitch.

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Why This Comparison Matters Right Now

Three separate events collided in the SIEM market during the first half of 2026. First, Microsoft began charging for Security Compute Units consumed by Sentinel’s entity analyzer feature starting April 1, 2026, adding a new line item to bills that were already dominated by per-gigabyte analytics tier costs. Second, Cisco continued folding Splunk Enterprise Security into its broader XDR strategy, rolling out bidirectional sync between Cisco XDR and Splunk ES so that incidents detected in one system automatically spawn investigations in the other, complete with AI-generated summaries. Third, and most disruptive, Sophos closed its $859 million acquisition of Secureworks in February 2025 and spent the following eighteen months rebuilding the Taegis analytics engine into what became Sophos Fusion.

Sophos Fusion replaces Sophos Central as the company’s management console and bundles Next-Gen SIEM, XDR, and MDR on a shared data layer. What makes it relevant to a Sentinel-vs-Splunk decision isn’t brand loyalty, it’s the pricing model. Sophos is charging by user and server rather than by data volume, which directly attacks the biggest pain point in both Sentinel and Splunk ES billing: unpredictable costs when log volume spikes during an incident, a cloud migration, or a compliance audit.

Microsoft Sentinel: Azure-Native SIEM With a New AI Tax

Microsoft Sentinel remains a cloud-native SIEM built directly on Azure Monitor and Log Analytics, which means it lives or dies by your existing Azure footprint. There’s no separate Sentinel infrastructure to stand up; you enable it against a Log Analytics workspace and start connecting data sources. That simplicity is Sentinel’s biggest structural advantage over Splunk, which typically requires more deployment planning whether you run it on-prem or in Splunk Cloud, and the cost gap between the two has been narrowing: a February 2025 UnderDefense pricing analysis found Sentinel’s pay-as-you-go rate starting around $5.22 per GB, already undercutting Splunk’s typically steeper SIEM ingest pricing before any volume discounts are applied.

Sentinel runs a two-tier storage model. The analytics tier handles real-time detection and interactive querying, with 90 days of retention included at no extra charge and extension available up to two years at additional cost, according to Microsoft’s Sentinel billing documentation. Microsoft sweetened that entry point further in October 2025 with a promotional 50 GB commitment tier, running through December 2026 and aimed squarely at pulling Splunk’s small-and-midsize customers onto Sentinel, with the discounted pricing locked in through March 2027 for anyone who signs up during the promo window. A newer data lake tier automatically mirrors analytics-tier data into cheaper long-term storage, priced separately at roughly $0.05 per GB for ingestion, $0.10 per GB for processing, and $0.026 per GB per month for storage. That data lake tier exists specifically because customers complained about paying premium analytics-tier rates just to keep logs around for compliance purposes.

On the AI side, Sentinel integrates with Microsoft Security Copilot for assisted investigation and ships an entity analyzer for behavioral analytics, but that entity analyzer now consumes billable Security Compute Units as of April 1, 2026. For teams that were budgeting purely on ingestion volume, that’s a new variable to model. Microsoft continues to expand Sentinel’s connector catalog, adding sources like Cyren Threat Intelligence in its 2026 RSA Conference announcements, and the platform is generally recognized for having one of the deepest built-in connector ecosystems of any cloud SIEM, spanning Microsoft 365, Azure, AWS, GCP, and hundreds of third-party security tools.

Splunk Enterprise Security: Cisco’s Anchor SIEM, Still Ingest-Priced

Splunk Enterprise Security has always been the SIEM security teams love for its search language and dashboards and dread for its bill. That dynamic hasn’t changed much since Cisco completed its acquisition of Splunk in March 2024, though the ownership change is starting to show up in the product. The headline development is bidirectional integration with Cisco XDR: incidents flagged in Cisco XDR now automatically generate structured investigations inside Splunk ES, complete with AI-written summaries and observable indicators, and any updates analysts make in ES sync back to XDR.

Pricing is where Splunk ES still diverges hardest from its two competitors here. The platform runs on a base ingest model, where you pay per gigabyte per day indexed, layered with a newer workload pricing option based on Splunk Virtual Compute (SVC) units that decouples cost from raw ingestion caps. According to Splunk’s own pricing overview, the platform still quotes primarily on request rather than publishing flat rate cards, and independent pricing trackers like CostBench put typical ES list pricing at $150 to $2,000 per GB/day depending on volume and contract terms, with most mid-sized teams landing around $690 per GB/day, which works out to roughly $69,000 a year for a 100 GB/day deployment before implementation and training costs. Larger benchmarks from Expanso put a 500 GB/day Splunk Cloud plus ES deployment with one year of retention at $1.2 million to $2.5 million annually. Multiple pricing guides also note that the Enterprise Security add-on itself typically adds 50 to 100 percent on top of the base Splunk platform license, meaning the number on the base platform quote is never the real number.

Deployment flexibility is a genuine strength. Splunk ES runs on-prem, in a customer-managed cloud, or as Splunk Cloud SaaS, which matters for regulated industries that can’t put security telemetry in a shared multi-tenant environment. Retention is configurable per index rather than fixed, though most published cost models assume a one-year retention baseline for budgeting purposes.

Sophos Fusion: The New Next-Gen SIEM Betting Against Per-GB Pricing

Sophos Fusion is the newest entrant here by a wide margin, and its pitch is built entirely around the thing that frustrates buyers about the other two platforms: unpredictable, volume-driven billing. According to Sophos’s Next-Gen SIEM product page, the platform prices by protected users and servers rather than data volume, with the company explicitly marketing “no ingestion-based fees, no penalties for adding more data, no surprise costs when volumes increase.” Exact per-seat pricing wasn’t published at launch, but the structural difference from Sentinel and Splunk is real and verifiable in Sophos’s own materials.

Retention is the other headline number: Sophos Next-Gen SIEM ships with one year of retention by default, with upgrade paths to 3, 5, 7, or 10 years, all built into the predictable pricing model rather than billed as incremental storage. That’s a meaningfully longer default retention window than either Sentinel’s 90-day interactive tier or Splunk’s typical one-year cost-modeling baseline, and it matters for compliance regimes like HIPAA, PCI DSS, and SEC recordkeeping rules that require multi-year audit trails.

Under the hood, Fusion runs on Taegis analytics inherited from the $859 million Secureworks acquisition Sophos closed in February 2025. Sophos describes Fusion as an “AI-native cybersecurity defense system” unifying SIEM, XDR, and MDR on a shared data layer, according to the company’s launch announcement covered by Orange Tech Center’s coverage of the August 15 GA rollout. The XDR component carries over thousands of Taegis detectors plus built-in SOAR automation for playbook-driven response. Fusion also supports more than 500 third-party integrations feeding into that same data layer, and Sophos is bundling its Email Monitoring System at no additional charge for MDR, MDR Plus, and XDR customers, a move clearly aimed at undercutting bundled pricing from Microsoft and Cisco-Splunk.

Market Position and Customer Base

None of the three vendors has published a clean, apples-to-apples 2026 market-share breakdown for this specific SIEM comparison, but the directional picture is clear enough to inform a shortlist decision. Splunk remains one of the highest-revenue SIEM platforms by dollar volume, a position that predates the Cisco deal and hasn’t visibly eroded since Cisco completed its acquisition in March 2024. What’s changed is the strategic framing: Splunk is increasingly positioned as the data-analytics core of Cisco’s broader security and observability portfolio rather than a standalone product competing purely on SIEM features.

Microsoft Sentinel benefits from default distribution: any organization already paying for Microsoft 365 E5 or an equivalent Azure security bundle has a low-friction path to enabling Sentinel without a separate procurement cycle, which is a structural advantage neither Splunk nor Sophos can fully replicate. That bundling effect is a major reason Sentinel shows up so often on cloud-native SOC shortlists even when its raw feature set doesn’t clearly beat the alternatives.

Sophos enters this specific fight from a position of strength in adjacent markets, endpoint protection and managed detection and response, rather than as an established SIEM vendor. Sophos MDR already had a large existing customer base before Fusion’s launch, and the company’s own case-study library, including deployments like Royal Media Services, shows a track record in managed response that predates the Next-Gen SIEM product by years. Fusion’s real bet is that those existing MDR and endpoint customers upgrade into the unified console rather than shop competitors for a standalone SIEM, a much lower-friction sales motion than winning net-new logo customers away from Splunk or Microsoft.

Full Specs Comparison: Microsoft Sentinel vs Splunk vs Sophos Fusion

The table below lines up the technical specs that matter most when narrowing a SIEM shortlist, drawn from official vendor documentation and launch materials as of August 2026.

Spec	Microsoft Sentinel	Splunk Enterprise Security	Sophos Fusion (Next-Gen SIEM/XDR)
General availability	Established (ongoing feature updates)	Established (Cisco-owned since March 2024)	August 15, 2026
Pricing model	Per-GB ingestion + commitment tiers + data lake tier	Per-GB/day ingest or SVC workload units	Per user/server, not data volume
Default log retention	90 days interactive (analytics tier)	Configurable per index; ~1 year typical baseline	1 year default
Max retention available	Up to 2 years analytics, longer via archive/lake tiers	Contract-dependent	Up to 10 years
Deployment model	Cloud-native SaaS on Azure only	On-prem, hybrid, or Splunk Cloud SaaS	Cloud-hosted SaaS (Fusion console)
Underlying analytics engine	Azure Monitor / Log Analytics	Splunk indexing + Cisco XDR sync	Secureworks Taegis analytics
AI/ML features	Security Copilot, entity analyzer (billable SCUs)	ML Toolkit, risk-based alerting, Cisco XDR AI summaries	AI-native parsers, thousands of Taegis detectors
Third-party integrations	Hundreds of native connectors	Broad app ecosystem + Cisco XDR/SOAR	500+ integrations into shared data layer
SOAR/automation	Logic Apps playbooks	Adaptive Response + Cisco SOAR sync	Built-in Taegis SOAR playbooks
Multicloud support	Yes, via connectors (AWS, GCP)	Yes, platform-agnostic	Yes, via 500+ integrations
MDR bundled option	Not native (requires separate Defender Experts)	Not native (requires separate MDR partner)	Native, includes free Email Monitoring System
Parent company	Microsoft	Cisco	Sophos (Thoma Bravo-backed)

Pricing Breakdown: What Each Platform Actually Costs

Pricing is the single biggest differentiator in this comparison, and it’s also the hardest to pin down cleanly because two of the three vendors still quote in per-gigabyte terms that scale unpredictably. Here’s what the published numbers and third-party pricing trackers show for representative deployment sizes.

Deployment scenario	Microsoft Sentinel	Splunk Enterprise Security	Sophos Fusion
Pay-as-you-go base rate	~$2.46/GB (West US 2 baseline, Log Analytics + Sentinel fee combined)	$150–$2,000/GB per day; ~$690/GB/day typical mid-tier	Not volume-priced (per user/server)
100 GB/day committed tier	~$1.23/GB (~$123/day commitment pricing)	~$69,000/year typical implementation	Flat per-seat, volume-independent
Mid-market SOC (~200 GB/day)	Est. $150,000–$300,000/year at $2–$4/GB effective	Est. $220,000–$310,000/year list (100 GB/day base, before discount)	Predictable per-seat billing, no ingestion surcharge
Large enterprise (~500 GB/day)	Scales via commitment tiers, ~$1.075/GB at 10,000 GB/day	$1.2M–$2.5M/year (Splunk Cloud + ES + 1-year retention)	Not published; scales with headcount/servers, not ingestion
Long-term archive/retention add-on	Data lake tier: $0.05/GB ingest, $0.026/GB/month storage	Contract-dependent, often a separate line item	Included up to 10 years in base Next-Gen SIEM pricing
ES/add-on premium over base platform	N/A (Sentinel is billed as its own service)	Typically 50–100% on top of base Splunk platform license	N/A (SIEM/XDR/MDR bundled)

Two things stand out. First, both Sentinel and Splunk ES get cheaper per gigabyte as volume scales up through commitment tiers, which rewards large, predictable environments and punishes smaller teams or anyone with spiky log volume during incidents. Second, Sophos Fusion’s per-user/server model sidesteps that volatility entirely, but Sophos hasn’t published exact per-seat numbers, so budget-conscious buyers will need to request a quote before assuming it’s cheaper at their specific headcount and server count. For a 500-person company with a lean server footprint, Fusion could easily undercut both incumbents. For a data-heavy environment with a small headcount but massive log volume, ingest-based pricing from Sentinel might still come out ahead.

Total Cost of Ownership: Beyond the List Price

List price is only part of the real cost of running any of these three platforms, and pricing guides that focus purely on per-GB or per-seat rates tend to understate what a SOC actually spends in year one. Implementation, analyst training, and detection-content tuning add up fast regardless of vendor. CostBench’s calculator, for example, puts a 10-person team’s Splunk ES license at $82,800 a year on paper, but the same model shows a year-one total closer to $124,200 once implementation, support, and training are included, a 50 percent gap between the quoted license price and what actually hits the budget.

That gap matters differently for each platform. Sentinel’s tight Azure integration tends to shrink the implementation gap for teams already comfortable with Azure Monitor, since there’s less new infrastructure to learn. Splunk’s more powerful but more complex search language cuts the other way, requiring real analyst ramp-up time even for teams with prior SIEM experience. Sophos Fusion is the wildcard here: its guided, detector-based UI is designed to lower the training curve compared to writing custom KQL or SPL, but because the platform only reached general availability on August 15, 2026, there’s no multi-year track record yet showing what real-world implementation timelines look like at scale.

Detection, Retention, and Integration Benchmarks

Independent, apples-to-apples MTTD and MTTR benchmarks across all three platforms aren’t publicly available as of August 2026; Gartner and Forrester gate their detailed Magic Quadrant and Wave metrics behind paid licenses, and even publicly available SANS Institute white papers on SIEM effectiveness tend to focus on methodology and general benchmarking guidance rather than vendor-specific head-to-head scores. None of the three vendors has published a head-to-head detection-speed study against these two specific competitors. What is verifiable, and arguably more useful for a purchasing decision, is the retention, integration, and architecture data each vendor has put on the record.

• Retention ceiling: Sophos Fusion’s 10-year maximum retention beats Sentinel’s roughly 2-year analytics tier ceiling and Splunk ES’s typical 1-year cost-modeling baseline by a wide margin, based on figures published by Microsoft’s billing docs and Sophos’s product page.
• Integration breadth: Sophos cites 500+ third-party integrations for Fusion; Microsoft doesn’t publish a fixed connector count but is widely recognized for one of the deepest catalogs in the category, spanning its own 365/Azure stack plus AWS and GCP; Splunk leans on its broader app ecosystem plus the new Cisco XDR sync layer.
• Compute pricing shift: Both Splunk (SVC workload units) and Microsoft (Security Compute Units for the entity analyzer) have moved toward compute-based billing components in 2026, a trend CostBench and Expanso pricing trackers both flag as a response to customer pushback on pure ingestion pricing.
• Vendor cost benchmarks: VendorBenchmark’s 2026 SIEM pricing table shows average paid Splunk ES rates around $38/GB/day at mid-volume, dropping to $14–$21/GB/day at the highest negotiated volumes, an order-of-magnitude spread that shows how much negotiating leverage matters with Splunk specifically.

For teams that need a hard MTTD/MTTR number for a procurement scorecard, the honest answer is to request a proof-of-concept with your own log sources rather than trust a vendor-supplied benchmark, since none of the three companies has published a controlled, third-party-verified detection-speed comparison against these specific two competitors.

AI and Machine Learning Detection Capabilities

All three vendors now market themselves as “AI-powered” or “AI-native,” but the implementations differ in where the AI sits in the workflow. Microsoft Sentinel pairs with Security Copilot for natural-language investigation assistance and runs a dedicated entity analyzer for behavioral profiling, though that analyzer now bills separately via Security Compute Units starting April 2026, a cost most Sentinel customers hadn’t budgeted for the previous year.

Splunk ES layers machine-learning anomaly detection and risk-based alerting on top of its core search engine, and the Cisco ownership has added a genuinely useful capability: incidents flagged in Cisco XDR now generate AI-written summaries automatically inside Splunk ES investigations, cutting down the manual triage work analysts used to do by hand. Sophos Fusion leans hardest into the “AI-native” framing, built around Secureworks’ Taegis analytics engine with thousands of pre-built detectors and AI-assisted data parsers that reduce the manual work of onboarding new log sources, a common pain point with traditional SIEM deployments.

Sample Sentinel KQL vs Splunk SPL Query Comparison

Query language is a real switching cost that pricing tables don’t capture. Here’s the same basic failed-login detection written in Sentinel’s Kusto Query Language and Splunk’s Search Processing Language, to illustrate the learning curve teams face when migrating.

// Microsoft Sentinel (KQL)
SigninLogs
| where ResultType != "0"
| summarize FailedAttempts = count() by UserPrincipalName, bin(TimeGenerated, 1h)
| where FailedAttempts > 10

// Splunk Enterprise Security (SPL)
index=auth sourcetype=okta:signin result!="SUCCESS"
| bin _time span=1h
| stats count as FailedAttempts by user, _time
| where FailedAttempts > 10

Sophos Fusion doesn’t expose a raw query language in the same way; its Taegis-based detection relies on pre-built detectors and a guided analyst UI rather than free-form querying, which lowers the skill floor for smaller teams but gives power users less flexibility to build custom correlation logic compared to KQL or SPL.

Architecture and Deployment Models

Microsoft Sentinel is locked to Azure. There’s no on-prem option and no other cloud host it, though its connectors reach into AWS, GCP, and on-prem infrastructure via agents. That’s a dealbreaker for organizations without an existing Azure footprint, and a natural fit for anyone already standardized on Microsoft 365 and Azure infrastructure, since Sentinel shares billing, identity, and networking with the rest of the Azure estate.

Splunk Enterprise Security offers the most deployment flexibility of the three: on-premises for regulated environments that can’t put telemetry in shared cloud infrastructure, self-managed cloud for teams that want AWS or Azure hosting under their own control, or Splunk Cloud as a fully managed SaaS option. That flexibility comes at the cost of more operational overhead; someone has to manage indexers, forwarders, and search head clusters unless you’re fully on Splunk Cloud.

Sophos Fusion is delivered exclusively as a cloud-hosted SaaS console, the successor to Sophos Central. Endpoints, firewalls, email gateways, and cloud accounts all connect into Fusion’s unified data layer, which Sophos calls a shared context lake feeding SIEM, XDR, and MDR from the same telemetry pool. There’s no self-hosted option, which simplifies operations for smaller IT teams but means organizations with strict data-residency requirements need to confirm Sophos’s regional hosting options before committing.

Data residency is worth flagging separately from raw deployment flexibility. Sentinel’s data stays inside whatever Azure region you provision your Log Analytics workspace in, which is straightforward for teams already navigating Azure’s regional compliance boundaries. Splunk’s on-prem and self-managed cloud options give the most direct control over where data physically lives, which is exactly why regulated industries default to it. Sophos hasn’t published a full list of regional hosting options for Fusion at launch, so any organization with strict data-sovereignty requirements, EU public sector, healthcare, or defense-adjacent contractors, should get written confirmation of regional hosting before signing a contract rather than assuming parity with the other two platforms.

Real-World Deployment Examples

Here’s how these platforms show up in practice across different organization types and sizes, based on vendor case studies and published pricing benchmarks.

• Mid-market SOC on Azure (200 GB/day): A company already running Microsoft 365 E5 and Azure infrastructure typically lands in the $150,000–$300,000/year range for Sentinel ingestion alone at effective rates of $2–$4/GB, according to vendor benchmark pricing analysis, making it a natural extension rather than a new procurement.
• Regulated financial services firm on Splunk Cloud: Organizations needing on-prem or self-managed hosting for compliance reasons gravitate to Splunk ES specifically because of its deployment flexibility, even though CostBench pricing data shows they’ll typically pay $220,000–$310,000/year list price for a 100 GB/day deployment before negotiated discounts.
• Enterprise SOC with Cisco networking investment: Companies already running Cisco XDR benefit from the new bidirectional sync with Splunk ES, where incidents auto-generate AI-summarized investigations, reducing manual correlation work for security analysts juggling both platforms.
• Royal Media Services on Sophos MDR: Sophos’s own case study library cites Royal Media Services shifting from an outsourced SOC model to Sophos MDR for proactive global threat monitoring, a deployment pattern that now feeds directly into the unified Fusion console for existing Sophos customers.
• Lean IT team choosing Sophos Fusion for predictable billing: Small and mid-sized businesses with limited security headcount but a compliance mandate for multi-year log retention are the clearest fit for Fusion’s per-user/server model, since they avoid the ingestion-volume risk that comes with a ransomware incident suddenly spiking log volume mid-contract on Sentinel or Splunk.

5 Use Cases: Which Platform Fits Which Team

Matching the right SIEM to your environment comes down to your existing infrastructure, your compliance retention requirements, and how predictable your log volume actually is. Here’s how the three stack up across common scenarios.

• Already standardized on Microsoft 365/Azure: Sentinel wins on integration simplicity and shared billing, even with the new Security Compute Unit charges factored in. There’s no competitive reason to bolt on a third-party SIEM when your identity, email, and endpoint stack are all Microsoft already.
• Need on-prem or self-hosted deployment for regulatory reasons: Splunk ES is the only one of the three that supports true on-premises deployment, making it the default choice for government, defense, and heavily regulated finance environments that can’t put security telemetry in a shared SaaS tenant.
• Small security team, big compliance retention mandate: Sophos Fusion’s up-to-10-year retention window bundled into predictable per-seat pricing is purpose-built for lean teams facing HIPAA, PCI DSS, or SEC recordkeeping requirements without a dedicated data engineering function to manage tiered storage.
• Already running Cisco network and XDR infrastructure: Splunk ES’s bidirectional Cisco XDR sync makes the two products function as one investigation workflow, which is hard to replicate by bolting a competing SIEM onto an existing Cisco security stack.
• Budget-sensitive team worried about incident-driven cost spikes: Fusion’s volume-independent pricing removes the single biggest budgeting risk in both Sentinel and Splunk: a major incident that triggers a log volume spike right when you can least afford a surprise bill.

Migration Guide: Moving Between SIEM Platforms

Switching SIEM platforms is a multi-month project, not a weekend cutover. Here’s a realistic sequence for teams evaluating a move to or from any of these three.

• Step 1 — Inventory current data sources and retention requirements. Document every log source feeding your current SIEM, its volume, and the compliance-mandated retention period, since this determines whether Sentinel’s tiered retention, Splunk’s per-index configuration, or Sophos’s flat multi-year retention fits best.
• Step 2 — Run a parallel proof-of-concept. Connect your highest-volume and highest-risk log sources (identity provider, endpoint, cloud infrastructure) to the candidate platform without disconnecting your existing SIEM, and compare detection coverage over a 30-day window.
• Step 3 — Rebuild detection content. Sentinel’s KQL, Splunk’s SPL, and Sophos’s Taegis detector library are not interchangeable. Budget real analyst time to port or rebuild custom detection rules; don’t assume a lift-and-shift is possible.
• Step 4 — Validate integrations before cutover. Confirm every third-party tool you rely on (ticketing, SOAR, threat intel feeds) has a working connector on the new platform; Sophos’s 500+ integrations, Sentinel’s native connector catalog, and Splunk’s app ecosystem all cover the basics but diverge on niche tools.
• Step 5 — Run dual-ingestion during the transition window. Keep both SIEMs live for at least one full billing cycle to compare alert volume, false positive rates, and analyst workload before fully decommissioning the old platform.
• Step 6 — Migrate historical data or accept a retention gap. None of the three platforms offers a simple bulk import from a competitor; plan for either an expensive custom export/import project or accepting that historical data older than your parallel-run window stays in the old system in read-only mode.
• Step 7 — Decommission and reallocate budget. Once detection parity is confirmed, sunset the old platform’s licensing and redirect that budget line, factoring in the new platform’s actual first-year cost including implementation and training, not just the list price quote.

Pros and Cons of Each Platform

Microsoft Sentinel

Pros: Deepest native integration with Microsoft 365 and Azure; no separate infrastructure to manage; strong connector catalog; Security Copilot AI assistance for investigations; data lake tier for cheap long-term storage.

Cons: Locked to Azure with no on-prem option; new Security Compute Unit charges add billing complexity; per-GB pricing still punishes volume spikes; 90-day default interactive retention is short compared to Fusion’s baseline.

Splunk Enterprise Security

Pros: Most flexible deployment options (on-prem, hybrid, or cloud); powerful search language for custom detection logic; new bidirectional Cisco XDR integration streamlines investigations; workload pricing option decouples cost from raw ingestion caps.

Cons: Highest total cost of the three at scale, with ES routinely adding 50–100% on top of base platform licensing; pricing remains quote-based and opaque; steeper operational overhead for self-managed deployments; retention isn’t standardized out of the box.

Sophos Fusion

Pros: Predictable per-user/server pricing with no ingestion penalties; up to 10 years of retention built into the base price; native MDR and XDR bundled rather than sold separately; free Email Monitoring System for MDR/XDR customers; 500+ integrations at launch.

Cons: Brand new platform (GA August 15, 2026) with no long-term track record; exact per-seat pricing not publicly disclosed; no self-hosted deployment option; less flexible free-form querying compared to KQL or SPL for teams that want to build highly custom detection logic.

The Verdict: Which SIEM Wins in 2026

There’s no single winner here, because the three platforms are optimized for genuinely different buyers. If your organization already runs on Microsoft 365 and Azure, Sentinel remains the path of least resistance despite the new Security Compute Unit charges, since the integration savings usually outweigh the added billing complexity, and Microsoft’s October 2025 promotional 50 GB commitment tier, with pricing locked through March 2027, makes the entry cost even harder to beat for smaller Azure shops. If you need on-premises deployment for regulatory reasons or you’re already committed to Cisco’s networking and XDR stack, Splunk Enterprise Security is still the only real option among these three, even at $690 per GB/day and up, though that same Sentinel promo is explicitly designed to peel off Splunk’s SMB customer base before contracts renew.

The most interesting development is Sophos Fusion, not because it’s proven, it launched barely three days before this article published, but because its per-user/server pricing model directly targets the exact pain point that shows up in every Sentinel and Splunk pricing conversation: the fear of an incident-driven volume spike blowing up next month’s invoice. For lean security teams with multi-year compliance retention mandates and no existing Azure or Cisco lock-in, Fusion is worth a proof-of-concept specifically to test whether its Taegis-based detection coverage holds up against Sentinel’s or Splunk’s more mature, battle-tested rule sets. Budget-wise, teams under 500 seats with modest server counts stand to see the clearest savings; high-volume, low-headcount environments should model actual numbers before assuming Fusion is cheaper.

Frequently Asked Questions

Is Sophos Fusion the same as Sophos Central?

No, but it replaces it. Sophos Fusion is the successor to Sophos Central, rebuilt as an AI-native platform unifying Next-Gen SIEM, XDR, and MDR on a shared data layer, with the SIEM and XDR components reaching general availability on August 15, 2026.

How much does Microsoft Sentinel cost per month?

Sentinel’s pay-as-you-go analytics tier runs roughly $2.46 per GB ingested in baseline regions like West US 2, dropping to around $1.23 per GB at the 100 GB/day commitment tier and further at higher volumes, according to Microsoft’s own Azure pricing documentation; a separate February 2025 UnderDefense pricing analysis pegged entry-level pay-as-you-go rates as low as $5.22 per GB depending on region and workload, already narrowing the gap with Splunk’s steeper SIEM ingest costs. A separate, cheaper data lake tier handles long-term retention at $0.05 per GB ingestion.

Does Splunk Enterprise Security require Splunk Cloud?

No. Splunk ES can run on-premises, in a self-managed cloud deployment, or through Splunk Cloud as a fully managed SaaS option, giving it the most deployment flexibility of the three platforms in this comparison.

What happened to Splunk after the Cisco acquisition?

Cisco completed its acquisition of Splunk in March 2024 and has since integrated Splunk Enterprise Security with Cisco XDR, adding bidirectional sync where incidents in one platform automatically generate AI-summarized investigations in the other. Splunk’s pricing has also shifted toward compute-based workload pricing alongside its traditional per-GB ingest model.

How long does Sophos Fusion retain log data?

Sophos Next-Gen SIEM, part of the Fusion platform, defaults to one year of retention with optional upgrades to 3, 5, 7, or 10 years, all built into its predictable per-user/server pricing rather than billed as separate storage tiers.

Can I migrate detection rules directly between Sentinel, Splunk, and Sophos Fusion?

No. Sentinel uses Kusto Query Language (KQL), Splunk uses Search Processing Language (SPL), and Sophos Fusion relies on pre-built Taegis detectors rather than free-form queries. Migrating between any two of these platforms requires manually rebuilding or re-tuning detection content, not a direct import.

Which SIEM is cheapest for a small business?

It depends on headcount versus log volume. Sophos Fusion’s per-user/server pricing tends to favor small teams with modest server counts, while Sentinel’s commitment tiers can be competitive for Azure-native shops with predictable, moderate log volume. Splunk ES is rarely the cheapest option at small scale given its ingest pricing and the 50–100% Enterprise Security add-on premium.

Does Sophos Fusion include XDR and MDR, or are they separate purchases?

Fusion bundles Next-Gen SIEM, XDR, and MDR on the same platform and shared data layer, unlike Sentinel and Splunk, where SIEM, endpoint detection, and managed response typically come from separate products or third-party MDR partners.