Concurrent licensing and device licensing are two families of software license metrics that do not count authorized individuals. A concurrent metric counts how many users, sessions or endpoints use the software at the same moment and licenses the peak. A device metric counts the machines on which the software runs or from which it is accessed, regardless of how many people use them. IBM’s Concurrent User illustrates the first: the licensee must obtain entitlements “for the maximum number of Concurrent Users simultaneously accessing the Program.”[1] Citrix’s Per device license illustrates the second: it “allows an unlimited number of users per device.”[2]
Microsoft’s client access licenses (CALs) sit between the two, because a CAL may be assigned either to a user or to a device.[3] Document-based metrics, such as SAP Digital Access, form an adjacent family: they license indirect and machine access by the business records it creates rather than by the people or devices involved.[4]
History
The dated vendor documents show concurrent models being narrowed or separated from other models. Autodesk retired its one-year multi-user subscription, which licensed concurrent Authorized Users against a license server, on 6 February 2023.[5] Citrix’s License types page (August 2026) keeps Concurrent and User/device as distinct models and states that Citrix Virtual Desktops Standard Edition concurrent licenses cannot be converted to user/device licenses or the reverse.[2] Microsoft’s CALs are version-bound: a CAL allows access to the corresponding version of the server software or earlier versions, not later ones.[3] SAP’s Software Use Rights version 4-2026 set out the current document types and weights for Digital Access.[4]
Scope and definitions
Concurrent metrics
Vendors define the thing that is concurrent in different ways:
- A person. IBM counts a person accessing the Program at a point in time; the same person accessing several times simultaneously is still one Concurrent User.[1] Oracle’s Concurrent User is “each individual that may concurrently use or access the Programs,” but only customers or prospective customers, not employees or business partners.[6]
- A session. SAP’s Concurrent Sessions are “the aggregated numbers of sessions accessing the licensed Software at any 1 time,” where a session runs from logon to logoff or time out.[4] NetScaler Gateway’s Universal license limits concurrent user sessions to the number purchased, and a user logged on from more than one computer occupies a license for each session.[7]
- An endpoint. Citrix’s Concurrent license is “based on the originating endpoint deviceID,” is checked in on logoff or disconnect, and is not licensed per session.[2]
- A logged-in agent. Webex Contact Center counts the highest number of simultaneously logged-in agents, using four consecutive 15-minute sampling periods to accommodate shift changes.[8]
Device metrics
A device metric needs a definition of the device. Microsoft’s Device CAL allows access “from one device by any user,” and a hardware partition or blade is a separate device.[3] Adobe’s Computer is “a virtual or physical device,” and each virtual environment, including virtual machines and virtual processors, counts as a separate Computer.[9] Oracle’s Connected Device counts unique devices, such as sensors, meters and RFID readers, that exchange data with Oracle applications without human interaction.[6]
How it works
Measuring the peak
A concurrent count is only as good as the mechanism that measures it. Citrix checks a Concurrent license out to an endpoint when a session starts and back in when it ends; in Citrix DaaS, the service counts unique devices accessing simultaneously.[2] SAP requires the number of Concurrent Sessions on each Deployment to be limited by license key mechanisms, prohibits programs that cache or queue report requests, and requires Named User licenses for users of deployments with an unlimited number of sessions.[4] Autodesk’s multi-user offering limited concurrent Authorized Users to the maximum in the subscription documentation and restricted users to employees and on-premises contractors.[5]
Client access licenses
Microsoft’s server products under the Server/CAL and Per Core/CAL models combine a server or core license with access licenses. Except where the Product Terms say otherwise, “all server software access requires CALs or External Connector Licenses.”[10] The components are:
- A Base CAL, the minimum access license for standard server functionality, such as the Windows Server 2025 CAL.[10]
- An Additive CAL, which “must be used on conjunction with a base CAL,” such as the Windows Server 2025 Remote Desktop Services CAL.[3][11]
- An External Connector, assigned to a server and permitting access by External Users, defined as users who are not employees or onsite or near-full-time contractors.[3]
- A CAL Equivalent License, a User SL or suite that satisfies the CAL requirement where the CAL and ML Equivalency table says so.[12]
User and Device CALs may be combined. A CAL may not be reassigned within 90 days except for permanent hardware failure, end of employment, or temporary absence.[3] The choice between them is an arithmetic one: user CALs suit people with several devices, device CALs suit shared devices used in shifts.
Hybrid user or device assignment
Citrix’s User/device model automates that choice. The License Server assigns a user license by default and a device license when two or more users connect from an exclusively shared endpoint, using user and device IDs so that the smallest number of licenses is used. Assignments last 90 days from connection.[2] Separate Per user and Per device models also use a 90-day assignment period but do not optimize between the two.[2] On-premises user/device, user and device models allow a 10% overdraft “as a convenience, not as a license entitlement,” which must be purchased within 30 days of first use; Concurrent licenses have no overdraft.[2] Citrix Virtual Apps and Desktops also offers a 15-day burst mode of unlimited connections, again as a convenience.[2]
Document-based metrics
SAP licenses indirect and machine access to ERP through Digital Access. The SAP S/4HANA Digital Access package lets humans use S/4HANA through directly integrated non-SAP applications, and lets non-humans such as bots, sensors and devices use it, without Named User licenses; all such access “is licensed based exclusively upon the number of Documents created annually.”[4] SUR names nine Document Types, from Sales Document to Time Management Document. Each Document counts as 1, except Material Documents and Financial Documents, which count as 0.2; documents created automatically as a consequence of an earlier document of a different type are not counted.[4] The RISE with SAP private edition service description applies the same weights to its cloud Digital Access service.[13] Adobe’s Acrobat Services uses a comparable unit, the Document Transaction, defined as an initial API call that produces a Document, with page bands per Operation.[14]
Vendor comparison
Concurrent metrics in the catalog:
| Vendor | Metric (vendor name) | What is counted | Floor / threshold | Effective |
|---|---|---|---|---|
| IBM | Concurrent User | Maximum persons accessing simultaneously[1] | Not stated | 2026-08-31 |
| Oracle | Concurrent User | Individuals who may use concurrently; customers and prospects only[6] | None stated | 2024-06-15 |
| SAP | Concurrent Sessions | Sessions at any one time, key-limited per Deployment[4] | Licensed Level | 2026-04-20 |
| Citrix | Concurrent | Originating endpoint device during an active session[2] | No overdraft; 15-day burst | 2026-08-05 |
| Citrix | Universal license (NetScaler Gateway) | Concurrent user sessions[7] | Cap equals licenses purchased | 2025-09-27 |
| Cisco | Webex Contact Center Concurrent Agent | Highest simultaneous logged-in agents[8] | Not stated | 2026-08-31 |
| Autodesk | Multi User | Concurrent Authorized Users (retired offering)[5] | Subscription limit | 2026-08-28 |
Device, CAL and document metrics:
| Vendor | Metric (vendor name) | What is counted | Floor / threshold | Effective |
|---|---|---|---|---|
| Microsoft | User CAL | One user, any device[3] | One per user; 90-day reassignment | 2026-08-10 |
| Microsoft | Device CAL | One device, any user[3] | One per device | 2026-08-10 |
| Microsoft | External Connector | Server, for External Users[3] | One per server | 2026-08-10 |
| Microsoft | Device SL | Licensed Device for an Online Service[15] | Internet check every 90 days | 2026-08-10 |
| Citrix | User/device | User by default; device for shared endpoints[2] | 10% overdraft; 90-day assignment | 2026-08-05 |
| Citrix | Per device | Unique device ID, unlimited users[2] | 10% overdraft | 2026-08-05 |
| Adobe | Computer | Physical device or each virtual environment[9] | Two Computers, not simultaneously | 2024-06-18 |
| Adobe | Device-Based Software License | Installations on devices or VMs[16] | Installations not above licenses | 2024-06-18 |
| Oracle | Connected Device | Unique non-human devices exchanging data[6] | None stated | 2024-06-15 |
| ServiceNow | Devices | Devices as a capacity meter, auto-counted[17] | Order Form quantity | 2026-03-12 |
| SAP | Documents for SAP Digital Access | Documents created annually by Digital Access[4] | Weights 1.0 and 0.2 | 2026-04-20 |
| Adobe | Document Transaction | API calls that produce a Document[14] | Page bands per Operation | 2024-11-19 |
Related rules:
| Vendor | Rule | Kind | Effective |
|---|---|---|---|
| Citrix | User/device vs Concurrent counting definitions | Counting | 2026-08-05 |
| Citrix | Per user / Per device 90-day assignment (distinct from User/device) | Counting | 2026-08-05 |
| Citrix | License overdraft +10% | Floor / minimum | 2026-08-05 |
| Citrix | License burst mode — unlimited connections 15 consecutive days | Restriction | 2026-08-05 |
| Adobe | Device-based — installations must not exceed licenses | Restriction | 2024-06-18 |
| SAP | SUR Digital Access document types and weights | Counting | 2026-04-20 |
| SAP | PCE Digital Access — Material/Financial Documents = 0.2 | Counting | 2025-03-05 |
Relationship to other license models
Concurrent and device metrics are alternatives to named user licensing, and some vendors allow them to be combined. SAP lets SAP Business Intelligence users identified at logon and Concurrent Session licenses be purchased together for a Deployment.[4] Microsoft’s CALs are always paired with a server or core license, so Windows Server demand has a processor and core component and an access component.[10] Virtualization changes device counts: Adobe counts each virtual machine as a Computer, one of several overlays described in Virtualization and partitioning.[16]
Criticism and challenges
Concurrent licensing depends on enforcement and measurement that the licensee may not control. In Citrix Cloud, Citrix does not prevent launches when usage exceeds purchased licenses, so overuse becomes a compliance question rather than a technical block.[2] Citrix also warns that overdraft and burst capacity are conveniences, not entitlements.[2] Multiplexing does not reduce the number of Citrix user/device licenses required.[2] For device metrics, the treatment of virtual machines and partitions decides the count and differs by vendor. For document metrics, the licensee must be able to identify which documents were created through Digital Access rather than by licensed named users, a distinction that SAP draws by whether the user works through SAP user interfaces or through a directly integrated non-SAP application.[4]
Out of scope
This article does not cover CAL pricing, CAL suites in detail, or hardware device management. Vendor-specific detail is on Citrix User/device, Concurrent, and Flex licensing, Windows Server licensing, SQL Server licensing and SAP Named User and Digital Access licensing.