matrix-spec/content/rooms/v4.md

---
title: Room Version 4
type: docs
weight: 40
---

This room version builds on [version 3](/rooms/v3) using a different
encoding for event IDs.

## Client considerations

This room version changes the format form event IDs sent to clients.
Clients should already be treating event IDs as opaque identifiers, and
should not be concerned with the format of them. Clients should still
encode the event ID when including it in a request path.

Clients should expect to see event IDs changed from the format of
`$randomstring:example.org` to something like
`$Rqnc-F-dvnEYJTyHq_iKxU2bZ1CI92-kuZq3a5lr5Zg` (note the lack of
domain).

Though unchanged in this room version, clients which implement the
redaction algorithm locally should refer to the [redactions](#redactions)
section below for a full overview.

## Server implementation components

{{% boxes/warning %}}
The information contained in this section is strictly for server
implementors. Applications which use the Client-Server API are generally
unaffected by the intricacies contained here. The section above
regarding client considerations is the resource that Client-Server API
use cases should reference.
{{% /boxes/warning %}}

Room version 4 uses the same algorithms defined in [room version
3](/rooms/v3), however using URL-safe base64 to generate the event ID.

### Event IDs

{{% boxes/rationale %}}
Room version 3 generated event IDs that were difficult for client
implementations which were not encoding the event ID to function in
those rooms. It additionally raised concern due to the `/` character
being interpreted differently by some reverse proxy software, and
generally made administration harder.
{{% /boxes/rationale %}}

{{% rver-fragment name="v4-event-ids" withVersioning="true" %}}

## Unchanged from v3

The following sections have not been modified since v3, but are included for
completeness.

### Redactions

{{% rver-fragment name="v1-redactions" %}}

### Handling redactions

{{% rver-fragment name="v3-handling-redactions" %}}

### Event format

The event format is the same as [room version 3](/rooms/v3#event-format),
however the event IDs in the following example are updated to reflect
the changes in this room version.

{{% rver-fragment name="v4-event-format" %}}

### Authorization rules

{{% rver-fragment name="v3-auth-rules" %}}

### State resolution

{{% rver-fragment name="v2-state-res" %}}

### Canonical JSON

{{% rver-fragment name="v1-canonical-json" %}}