> ## Documentation Index
> Fetch the complete documentation index at: https://docs.goakt.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# API Changes (v4.0.0)

> Breaking changes and new APIs in v4.

A quick summary of v4.0.0 changes. For the complete migration guide, see [Migration from v3.x](/getting-started/migration-v3).

## Executive summary

v4.0.0 delivers **simplification** and **performance**:

| Theme                | Key changes                                                                   |
| -------------------- | ----------------------------------------------------------------------------- |
| **Unified APIs**     | Single actor reference (`*PID`), single lookup (`ActorOf`), unified scheduler |
| **Type flexibility** | `any` replaces `proto.Message`; CBOR for arbitrary Go types                   |
| **Remoting**         | Config-only public API; client is internal                                    |
| **Identity**         | `Path` interface replaces `*address.Address`                                  |
| **Performance**      | Low-GC serialization, lock-free type registry, single-allocation frames       |

## Quick migration reference

| From                           | To                                                      |
| ------------------------------ | ------------------------------------------------------- |
| `proto.Message` in handlers    | `any`                                                   |
| `goaktpb.*` types              | `actor.*` (e.g., `actor.PostStart`, `actor.PoisonPill`) |
| `ActorRef`                     | `*PID`                                                  |
| `ActorOf` → `(addr, pid, err)` | `ActorOf` → `(*PID, error)`                             |
| `LocalActor(name)`             | `ActorOf(ctx, name)`                                    |
| `RemoteActor(ctx, name)`       | `ActorOf(ctx, name)`                                    |
| `pid.Address()`                | `pid.Path()`                                            |
| `ctx.SenderAddress()`          | `ctx.Sender().Path()`                                   |
| `WithRemoting`                 | `WithRemote(config)`                                    |
| `address` package              | `internal/address`; use `Path` interface                |

## New additions

* **Pluggable serializers** — ProtoSerializer (default), CBORSerializer for any Go type
* **Path interface** — Location-transparent actor identity
* **Extended Logger** — Context-aware logging, `Enabled`, `With`, `Flush`, etc.
* **Slog and Zap implementations** — Low-GC logging options