Explicit regional placement disables WebSocket permessage-deflate while Smart Placement works

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Which Cloudflare product(s) does this pertain to?

Workers Runtime

What versions & operating system are you using?

• Wrangler: 4.85.1
• OS: Linux

Please provide a link to a minimal reproduction

I can provide a stripped repro if needed, but the key finding is that the only variable required to trigger this is Worker placement mode.

I reproduced it with:

• the stock Cloudflare Agents starter
• our real Worker app (aidan-agent)

Describe the bug

WebSocket permessage-deflate negotiation works normally when a Worker has either:

• no placement configured, or
• Smart Placement enabled with:

"placement": { "mode": "smart" }

But if I switch the Worker to an explicit regional placement pin:

"placement": { "region": "aws:eu-west-2" }

then the WebSocket upgrade still succeeds with 101 Switching Protocols, but Sec-WebSocket-Extensions disappears from the response.

So this is not a generic websocket compression failure. It appears to be specifically tied to explicit regional placement.

Exact observed behaviour

No placement configured

• 101 Switching Protocols
• Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits=15

Smart Placement

• 101 Switching Protocols
• Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits=15

Explicit regional placement (aws:eu-west-2)

• 101 Switching Protocols
• Sec-WebSocket-Extensions header missing

Steps to reproduce

1. Deploy a Worker that upgrades a request to a WebSocket.
2. Probe the same WebSocket endpoint with a request offering permessage-deflate.
3. Confirm that compression is negotiated when:
   • placement is omitted, and
   • placement.mode = "smart"
4. Change only the placement config to:

"placement": { "region": "aws:eu-west-2" }

5. Redeploy.
6. Probe the same endpoint again.
7. Observe that the upgrade still returns 101, but Sec-WebSocket-Extensions is no longer present.

Expected behaviour

If the runtime supports websocket compression for this Worker, changing placement mode should not silently disable permessage-deflate negotiation.

Actual behaviour

An explicit region pin appears to disable websocket compression negotiation, while Smart Placement and no placement do not.

Extra context

• I originally discussed this with Sunil Pai on Discord, so cc @threepointone.
• There is already a broader issue about permessage-deflate not being accepted in some cases, but this report is narrower: the trigger here is specifically the explicit placement pin.
• As a workaround, we switched our production path to Smart Placement and compression immediately came back.