Microsoft Sentinel and Splunk are both capable SIEMs, and most comparisons between them are written by someone selling one of them. So here is ours, with the bias declared up front: we are a Microsoft Solutions Partner and we have run Sentinel since 2019. That shapes what we are good at. It does not change what Splunk is good at, and pretending otherwise would not help you choose.
The honest summary is that these two products have different shapes rather than different quality levels, and the decision is usually settled by your estate and your operating model rather than by a feature list.
First, something that has changed
If you are reading older comparisons — including the earlier version of this article — most of them describe Splunk as an independent company, often a smaller one than Microsoft. That is no longer the case. Cisco completed its acquisition of Splunk in March 2024.
That matters for a buying decision in a way a feature table does not. Splunk now sits inside a networking and security portfolio, and the integration story you will be told has changed accordingly. If you are already a Cisco estate, that is a point in Splunk's favour that simply did not exist a few years ago. Any comparison that still frames this as "big Microsoft versus small Splunk" is out of date, and you should treat the rest of its conclusions with the same caution.
What each one actually is
Microsoft Sentinel
Sentinel is Microsoft's cloud-native SIEM, with SOAR capability built in rather than sold alongside. It runs on Azure, stores its data in Log Analytics, and is queried in KQL. There is no on-premises deployment option — it is cloud, or it is not Sentinel.
Its defining characteristic is proximity to the rest of the Microsoft security stack. Defender for Endpoint, Defender for Office, Defender for Cloud and Entra ID connect natively, and the signals arrive already normalised rather than needing a parser written for them. Microsoft has been progressively consolidating Sentinel into the Defender portal, so the direction of travel is a single console across the Microsoft estate rather than a SIEM sitting beside it.
Splunk
Splunk started as a machine-data platform and became a SIEM, and that heritage still shows — in a good way. It ingests more or less anything, it does not much care what shape the data is, and its search language, SPL, is genuinely powerful once somebody in the team knows it well.
It can run on-premises, in Splunk Cloud, or across both. Its app ecosystem is large and long-established, and the range of integrations available off the shelf is one of the strongest arguments for it. Enterprise Security and SOAR are separate products within the portfolio rather than capabilities included by default, which is worth understanding before you compare anything.
How they are charged — which decides more of this than anything else
We do not publish figures for anything, ours or anyone else's, because a number without a scope behind it is guesswork on both sides. What is worth understanding is the shape of each model, because the two are fundamentally different and it changes how you operate.
- Sentinel is consumption-based. You pay for what you ingest and retain, with commitment tiers that reduce the rate if you can predict your volume, and cheaper tiers for high-volume, low-value logs. Costs scale with data, so the discipline required is deciding what is genuinely worth ingesting.
- Splunk is licence-based, traditionally on daily ingest volume, with workload-based options introduced as an alternative. It is more predictable month to month, which finance departments like, and it can mean paying for headroom you are not using.
The practical consequence: Sentinel punishes indiscriminate log collection and rewards thinking about it, while Splunk front-loads the decision into the licence and then leaves you alone. Neither is cheaper in the abstract. The one that is cheaper for you depends on how much you ingest, how spiky it is, and whether you can forecast it — and on nothing that either vendor's comparison page will tell you.
Where Sentinel is the stronger fit
- You are already a Microsoft estate. If you run Microsoft 365 E5, Defender and Entra ID, the connectors are native, the identity signals are first-class, and a meaningful share of your security telemetry can be ingested at no additional cost. This is the single biggest factor, and for many organisations it settles the question on its own.
- You want SIEM and SOAR in one place. Automation rules and playbooks are part of the product, not a second purchase.
- You have no appetite for infrastructure. There are no indexers to size, no storage to provision, no upgrade weekends.
- Your volume is unpredictable. Consumption pricing absorbs a spike without a licence conversation.
Where Splunk is the stronger fit
This is the section most vendor comparisons skip, and skipping it is how they lose the reader who is actually evaluating both.
- You need on-premises or air-gapped deployment. Sentinel cannot do this. If you are in OT, defence, or a jurisdiction where the data physically cannot leave, Splunk is a real answer and Sentinel is not.
- Your estate is heterogeneous and unusual. If your critical telemetry comes from appliances, industrial systems and in-house applications rather than from Microsoft products, Splunk's ingest-anything heritage and app ecosystem are a genuine advantage.
- You already have deep SPL expertise. An experienced Splunk team is an asset, and re-platforming means rebuilding detections and retraining analysts. That cost is real and it is routinely left out of migration business cases.
- You are a Cisco estate. Post-acquisition, the integration argument now runs in Splunk's favour here in a way it did not before.
- You use it for more than security. Plenty of organisations run Splunk across IT operations and business analytics. Comparing it to a SIEM alone understates what it is doing for them.
The question that actually decides it
Not "which is the better SIEM". Ask instead: where does most of my security-relevant telemetry already live, and who is going to operate this at three in the morning?
The first half usually points clearly one way. A Microsoft-centric estate points at Sentinel; a mixed, on-premises or Cisco-centric estate points at Splunk, and the closer your answer is to "it depends", the more the second half of the question matters.
The part neither product page covers
A SIEM is not a solution. It is a place where alerts arrive.
Both of these platforms will detect things competently once tuned, and both will generate more alerts than an in-house team can triage. The failure mode we see is not choosing the wrong product — it is choosing a good one, deploying it properly, and then discovering that nobody owns the queue at two in the morning on a Sunday. The tool is the smaller half of the problem, and it is the half that comes with a sales process and a business case attached.
Whatever you choose, budget for who operates it before you budget for the licence.
Where we stand
We run Managed Microsoft Sentinel, and Sentinel is the only hard requirement of our managed service — we build tooling to fit whatever else is in the estate. So if your answer is Splunk, we are not the right people to run it for you, and we would rather say that here than three meetings in.
If your answer is Sentinel, or you are not sure yet, the useful conversation is not about features. It is about what you are ingesting, what it will cost to ingest it, and who is on shift when something fires.