Orleans.FSharp vs Alternatives — F# Actor Frameworks Compared

Choosing an actor framework for F# distributed systems? This page compares Orleans.FSharp with the main alternatives: using Microsoft Orleans directly from C#/F#, Akkling (F# API for Akka.NET), and Proto.Actor.

Quick comparison

	Orleans.FSharp	C# Orleans (from F#)	Akkling (Akka.NET)	Proto.Actor
Actor model	Virtual actors	Virtual actors	Classic actors	Virtual + classic
F# API	Typed API records with grainContract / grainFor; siloConfig {} for hosting	Manual interop (class inheritance)	Native CEs (actorOf, spawnAnonymous)	None (C# API)
State persistence	Typed facets (usePersistentState)	Automatic (attribute)	Manual	Manual
Type safety	Compile-time checked API records, DU state	Runtime errors	Typed messages	Runtime errors
Clustering	Built-in (Redis, Azure, Kubernetes)	Built-in	Akka.Cluster	Built-in
.NET version	.NET 10	.NET 10	.NET 6+	.NET 6+
Testing	GrainArbitrary + FsCheck	Manual mocking	TestKit	Manual mocking
Backed by	Community (MIT)	Microsoft	Community	Community
Maintenance	Active	Active	Maintenance mode	Active

Orleans.FSharp vs C# Microsoft Orleans (used from F#)

You can use Microsoft Orleans directly from F# — but you end up writing C#-style code in F# syntax: class inheritance, mutable state, imperative patterns. Orleans.FSharp replaces that with immutable state, pattern matching, and computation expressions instead.

What changes

Aspect	C# Orleans from F#	Orleans.FSharp
Grain definition	Hand-written interface + inherit Grain() class	contract<string, CounterApi> { ... } + grainFor
State transitions	Mutable fields / this.State	Pure handlers returning newState, reply
Client proxies	C# source generator (needs a C# shim project)	Precompiled in the package — nothing to generate
Configuration	builder.UseOrleans(fun siloBuilder -> ...)	siloConfig { useLocalhostClustering; addMemoryStorage "Default" }
Serialization	Manual [<GenerateSerializer>] on classes	Same attribute, but on DUs — the natural F# choice
Testing	Write C#-style mocks	GrainArbitrary.forCommands<'Cmd>() + FsCheck

Code comparison

C# Orleans from F# (class inheritance):

type ICounterGrain =
    inherit IGrainWithStringKey
    abstract Increment: unit -> Task<int>
    abstract Value: unit -> Task<int>

// ...plus a C# shim project in the solution, because Orleans'
// proxy source generator does not run on F# projects.
type CounterGrain() =
    inherit Grain()
    let mutable count = 0

    interface ICounterGrain with
        member _.Increment() =
            count <- count + 1
            Task.FromResult count

        member _.Value() = Task.FromResult count

Orleans.FSharp (functional grain runtime):

type CounterApi =
    { increment: unit -> Task<int>
      value: unit -> Task<int> }

let counterContract =
    contract<string, CounterApi> {
        grainType "counter"
        version 1
        stringKey
        readOnly (_.value)
    }

let counter =
    grainFor counterContract {
        defaultState (fun () -> 0)
        handle      (_.increment) (fun _ctx n () -> task { return n + 1, n + 1 })
        handleQuery (_.value)     (fun _ctx n () -> task { return n })
    }

Same two operations on both sides. The functional version is immutable, the compiler checks every handler against CounterApi’s field types, and sealing the definition verifies each operation has exactly one handler — with no proxy-generation step anywhere.

Orleans.FSharp vs Akkling (Akka.NET)

Akkling provides an idiomatic F# API for Akka.NET — a port of the JVM Akka actor framework. The fundamental difference is the actor model: Microsoft Orleans uses virtual actors (always addressable, auto-activated), while Akka.NET uses classic actors (explicit lifecycle management).

Key differences

Aspect	Orleans.FSharp	Akkling (Akka.NET)
Actor lifecycle	Virtual — always exists, activated on demand	Explicit — must spawn, supervise, and restart
State persistence	usePersistentState facets	Manual Akka.Persistence integration
Failure handling	Automatic reactivation on another silo	Supervision trees (manual configuration)
Location transparency	Built-in grain directory	Akka.Cluster + shard regions
Stream processing	Stream.getStream + Stream.publish	Akka.Streams
Concurrency model	Single-threaded turns (with optional reentrancy)	Mailbox processing

When to choose Akkling

• You need fine-grained actor supervision hierarchies
• Your team already has Akka/Akka.NET experience
• You want the Akka.Streams API for complex stream processing

When to choose Orleans.FSharp

• You want virtual actors — no lifecycle management overhead
• You need automatic state persistence without boilerplate
• You want property-based testing with auto-generated command sequences
• You are targeting .NET 10
• You want built-in Kubernetes clustering support

Orleans.FSharp vs Proto.Actor

Proto.Actor is a cross-platform actor framework supporting both virtual and classic actor models. It does not have an F# API — you use the C# API directly.

Key differences

Aspect	Orleans.FSharp	Proto.Actor
F# API	Native computation expressions	C# API only
Virtual actors	Yes (Microsoft Orleans)	Yes (Proto.Cluster)
Serialization	F# DUs with [<GenerateSerializer>]	Protobuf (code generation)
State persistence	usePersistentState facets	Manual provider integration
Ecosystem	Microsoft Orleans ecosystem (Azure, Dashboard)	Standalone (gRPC-based)
Testing	GrainArbitrary + FsCheck	Manual

When to choose Proto.Actor

• You need cross-language support (Go, C#, Kotlin, Python)
• You want gRPC as the transport layer
• Your system is polyglot

When to choose Orleans.FSharp

• You are building a pure F#/.NET distributed system
• You want idiomatic F# with computation expressions
• You need the Microsoft Orleans ecosystem (Azure integration, Dashboard, extensive providers)

Feature matrix

Feature	Orleans.FSharp	C# Orleans	Akkling	Proto.Actor
F# computation expressions	Yes (137 operations across 8 builders)	No	Yes	No
DU state machines	Yes	No	Partial	No
Property-based testing	GrainArbitrary	No	No	No
Grain timers	onTimer keyword	RegisterTimer	Scheduler	Manual
Grain reminders	onReminder keyword	IRemindable	N/A	N/A
Event sourcing	journaledGrainFor { }	JournaledGrain	Akka.Persistence	Manual
Transactions	transactional + transactionalStateFrom	[Transaction] + TransactionalState	Saga pattern	Manual
Streaming	Stream module, onStream / onBroadcast	IAsyncStream	Akka.Streams	N/A
TLS/mTLS	useTls keyword	Manual config	Akka.Remote TLS	gRPC TLS
Kubernetes	useKubernetesClustering	Kubernetes package	Akka.Discovery	Kubernetes provider
Dashboard	addDashboard keyword	OrleansDashboard	Petabridge.Cmd	N/A
Health checks	enableHealthChecks keyword	Manual registration	N/A	gRPC health
OpenTelemetry	Orleans’ own activity sources and meter	Manual registration	Phobos	Manual

Performance

Orleans.FSharp runs on the Orleans runtime unchanged; it adds a dispatch layer, not a second transport.

• Where the work happens: a contract and a definition are sealed once, when the module that declares them initialises — not per call. An API shape is built once per record type and cached process-wide, and each operation’s argument and reply closures are precomputed at that point.
• Per call: one dictionary lookup and one preclosed delegate call on top of the Orleans call itself. The repository’s own dispatch benchmark holds that below 5% of calling the handler function directly, over 1,000,000 iterations.
• Network latency: dominates all real-world scenarios (microseconds to milliseconds).
• C# facade callers additionally pay DispatchProxy’s per-call boxing — see Calling from C#.

Recommendation summary

Use case	Recommended
New F# distributed system	Orleans.FSharp
Existing C# Orleans codebase, adding F#	Orleans.FSharp (interop is seamless)
Existing Akka.NET codebase	Akkling (unless migrating to Orleans)
Polyglot system (Go + C# + Python)	Proto.Actor
Learning actor model with F#	Orleans.FSharp (simplest mental model)

Next steps

• Getting Started — zero to working grain in 15 minutes
• How To — step-by-step distributed system tutorial
• FAQ — common questions about Orleans.FSharp
• Legacy API — maintenance documentation for earlier authoring models