One Session, Three Entry Points: The Sync Contract Cowork Just Set
On July 7, 2026, Anthropic expanded Cowork from the desktop app to web, iOS, and Android. You can hand off a task at your desk, check progress from your phone on the way out, and pick up the finished output on another device. That is not a UI convenience — it is a sync contract that decides where session state lives and which copy counts as truth. Whether you open it from the claude.ai home screen or the iOS/Android sidebar, the same session and files must appear, and whatever state the client holds locally is only a cache; the server record has to be the source of truth.
Fully Background: Closing the Laptop Doesn't Stop Execution
Cowork sessions run remotely by default. The agent loop and code execution run in an isolated sandbox on Anthropic-managed infrastructure, and sessions and files are saved to the account, not the device. Close the laptop and the task keeps running; a scheduled task can execute with no device online at all. Unlike a local background process, client connectivity and execution are entirely decoupled here.
Non-Coding Work Sits Unattended Longer
Usage data Anthropic shared alongside the launch shows more than 90% of Cowork usage wasn't software development — the largest categories were business operations and content creation. Unlike code review, which has a short built-in verification loop, this kind of work tends to sit longer before a human reopens it. The convenience of a session finishing with no device present also means an error or a stalled approval can sit unattended just as long.
Handoff Operations Guide: From Sync Design to Failure Recovery
Before putting cross-device sessions into production, fix numeric acceptance bars first. A reasonable starting point: session resume success rate above 99.5%, p95 delivery delay for background-completion notifications under 3 minutes, and a state-conflict rate from concurrent two-device access under 0.1%. Usage limits are doubled through August 5, so concurrent session volume has real room to grow — confirm these numbers before traffic climbs, not after.
The most common failure is two devices opening the same session and issuing conflicting instructions. If you tap cancel on your phone right as you tap approve on desktop, the server and client disagree about which state is final. Attach a last-known state version to every request via optimistic locking, reject immediately on a version mismatch, and force a re-fetch of the latest state.
A riskier case is reaching a human-approval point with no device online at all. Waiting indefinitely leaves the task stranded; silently falling back to a default and proceeding anyway can push through an action you cannot undo. Put a timeout on the approval-pending state whose default action is always pause-and-abort, and back it with a retry-with-backoff path to a fallback channel like email in case push notifications fail.
On resume, don't trust the local cache — force a hard resync against server state. Before shipping, test the scenario where a device is force-switched mid-task and the one where the notification channel dies while an approval is pending.
Log the session ID, device ID, last-sync timestamp, and completion status on every event, and mask task content or sensitive data out of mobile push payloads.
Review failures weekly by device-transition scenario to see which combinations produce the most conflicts or missed notifications, and keep the changelog for sync logic separate from the one for notification channels — that separation is what lets you narrow down which deployment caused an incident.
Takeaways at a Glance
Cowork's web and mobile expansion pushed the device-independent execution model — the session keeps running on the server regardless of what's connected — into everyday operating practice. Fix resume success rate and notification delay as numbers, apply optimistic locking to concurrent access, back approval waits with a safe timeout and a fallback notification channel, and review device-transition scenarios on a regular cadence — then a session that finishes with no device online becomes something you can operate with confidence, not just a demo.
References
Claude Cowork on web and mobile: hand off work anywhere — Claude by Anthropic