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Anthropic moves Cowork's VM and inference to the cloud

productsThe Glonce editorsSimon Willison🔥66Glonce rating66Impact60Novelty60Relevance88Surprise40Players80Credibility78

Simon Willison, on 5 October 2026, quoted Felix Rieseberg of Anthropic explaining how Cowork is changing under the hood.

In the "old" version of Cowork, model inference ran in the cloud, but tool calls were executed in an Anthropic-provided virtual machine that Anthropic shipped to the user's computer. Rieseberg says the VM was added for capability, safety and security reasons, and it mapped in only the data the user explicitly added to the session. The trade-off was cost on the user's side: people loved what they could do with Claude, but did not love the disk, battery and performance cost of running the VM locally. They also did not love that closing the laptop meant the work stopped.

In the "new" version, Cowork runs both model inference and the VM in the cloud. Each session gets its own sandbox, which does not share state with other sessions. When the VM needs something on the user's device, such as a file, the desktop app is responsible for that file access tool call.

Rieseberg's summary is framed as a belief: Anthropic thinks this solves a lot of problems it has heard about, like using Cowork from a phone, keeping work running, or getting all the same power without losing battery to the VM. The quote is excerpted (it contains an omission) and ends with a pointer to a help page. Willison adds no commentary of his own.

Key facts

  • Old Cowork: model inference in the cloud, but tool calls ran in an Anthropic-provided VM shipped to the user's computer.
  • New Cowork: both model inference and the VM run in the cloud, and each session gets its own sandbox that shares no state with other sessions.
  • When the cloud VM needs something on the user's device, such as a file, the desktop app handles that file access tool call.
  • Anthropic says users disliked the disk, battery and performance cost of the local VM, and that closing the laptop stopped the work.
  • Anthropic says it thinks the change addresses using Cowork from a phone, keeping work running, and avoiding battery loss to the VM.

Why it matters

This is a change in where an AI agent product does its work. Before, part of Cowork's machinery lived on the user's own machine as a VM. Now the whole thing, model and sandbox, sits in the cloud. Rieseberg ties the move to concrete complaints: the local VM cost disk, battery and performance, and the work stopped when the laptop was closed.

Who it affects

Cowork users, mainly. Those on laptops are the ones Rieseberg points to, since the old design drained battery and halted when the lid closed. People who want to use Cowork from a phone are named as a group the change should help. The desktop app stays in the picture, because it handles file access when the cloud VM needs something from the user's device.

How to use it

The source gives no steps for switching over. What it does describe is how the new version behaves: each session runs in its own cloud sandbox, and when the VM needs a file from your device, the desktop app performs that file access tool call. Rieseberg's attribution line points to a help page, but its content is not included. The source gives no release date, rollout schedule or availability for the new cloud version.

How solid is it

This is a first-party explanation from an Anthropic employee, quoted by Simon Willison, so it describes intent and design rather than independent testing. Rieseberg frames the benefits as belief ("We think this solves a lot of problems"). The source gives no pricing, usage limits, or performance and battery measurements, and no figures on how many users complained.

Risks and caveats

The quote is excerpted, so the full mechanism of file access is not described. The source does not say whether the old local-VM version will be removed or remain available. Rieseberg says the original VM was added for capability, safety and security reasons; the quote describes the new per-session sandbox but does not compare the two designs on those points.

“We think this solves a lot of problems we've heard about (like using Cowork from a phone, keeping work running, or getting all the same power without losing battery to the VM)”

— Felix Rieseberg, Anthropic