Jamsocket’s homepage redirects to Modal’s July 10, 2025 acquisition announcement, which described continued operation during migration. Confirm present legacy-service access, support and commercial terms for the particular product; the announcement does not establish universal current availability or shutdown. Read the source ↗

Application platforms / Jamsocket alternative

A Jamsocket alternative depends on which stateful product you used

Jamsocket’s homepage currently redirects to Modal’s acquisition announcement. That announcement distinguishes the backend platform, Plane orchestrator, Y-Sweet synchronization backend, and ForeverVM Python REPL service. A migration should identify the actual product and its retained artifacts rather than treat all four as the same Linux sandbox.

Start buildingCompare capabilities ↓

Reviewed 2026-10-18 · Published by the Sandbox0 team

When Jamsocket fits

The Jamsocket/Modal ecosystem may fit applications that need its realtime backend, collaborative document synchronization, or stateful Python workflow. Confirm the currently supported migration path and effective service terms for the product you actually use.

When to consider Sandbox0

Consider Sandbox0 for a durable mutable Linux agent computer with online RootFS growth and supported paused file operations. It does not automatically replace collaborative document protocols, backend orchestration, or an application-level Python session service.

Capabilities

Jamsocket and Sandbox0: what persists?

Feature comparison with documentation and verification status
Environment and runtime lifetimeJamsocketNot established in this reviewSandbox0ttl and hard_ttl default to 0 (disabled). Configure idle pause and deletion policies for the same persistent sandbox identity; an idle running sandbox still accrues compute charges.Read documentation →
Persistent filesJamsocketStateful application products are identified, but their current retained-disk terms are not established by the transition notice.View evidence ↗Sandbox0The writable RootFS survives successful checkpoints, including software, system configuration, dependencies, and user data.Read documentation →
Whole RootFSJamsocketDocument sync and Python REPL state do not establish complete Linux RootFS retention.View evidence ↗Sandbox0Persistence extends beyond /workspace to paths such as /usr/local, /etc, and /home. Runtime tmpfs and virtual filesystems are excluded.Read documentation →
Release compute, keep stateJamsocketThe acquisition announcement does not specify a uniform machine pause/resume contract.View evidence ↗Sandbox0Pause compute between tasks; resume on available capacity. Default resume starts fresh processes from the saved filesystem.Read documentation →
Memory and process stateJamsocketStateful Python execution is not evidence of arbitrary VM process-memory capture across all products.View evidence ↗Sandbox0Experimental memory checkpoints can preserve compatible process state. Use memory: true on both pause and resume on a compatible deployment. A filesystem checkpoint alone does not preserve running processes.Read documentation →

Online RootFS growth

On growth-enabled images, Sandbox0 automatically expands the writable RootFS as free space runs low, within a configured sparse logical ceiling up to 64 TiB. Agent processes keep running. Growth is enabled in the qualified Cloud region; confirm activation for other regions. Existing images and snapshots retain their captured storage geometry. The ceiling is logical capacity, not preallocated host disk.

Realtime document state and a persistent REPL are not automatic growth of a durable complete Linux RootFS. Sandbox0 addresses the machine layer, while synchronization or REPL semantics may need to be retained separately.

Files while compute is paused

Sandbox0's Files API reads persistent files without resuming compute. Filesystem-only pauses also permit edits; retained-memory pauses are read-only and reject mutations with 409. SSH, SFTP, file watching, and runtime-only mounts require running compute.

See paused file operations →

An acquisition announcement is not a shutdown guarantee

Modal announced the transition on July 10, 2025 and said Jamsocket products would continue during migration. The present redirect confirms that transition context, but does not independently prove that every legacy product is available or ended today. Check existing account and contract access before planning a new integration.

Source 1 ↗Source 2 ↗

Python variables and synchronized documents are different from a whole computer

ForeverVM’s stateful REPL and Y-Sweet’s document synchronization preserve application-level state. Plane supplies orchestration. Those primitives may be essential to your app, but the announcement does not establish a uniform complete writable RootFS or VM-memory checkpoint contract across those products.

Source 1 ↗

Do not apply successor-platform prices to a legacy agreement

The current redirect is not a standalone Jamsocket rate card. Legacy account terms and a new Modal deployment may have different meters and included usage. Verify which product will run the workload; a Modal promotional footer is not proof of a current Jamsocket allowance.

Source 1 ↗Source 2 ↗

Pricing

Compare billing models, then price your workload

CPU allocation, memory, billing minimums, disk, plan fees, and supported workload differ. These meters are not equal-performance machine quotes. Confirm region, resource units, and included allowances before estimating a total.

Jamsocket

Pricing reviewed 2026-10-18

Current standalone Jamsocket rate
Current standalone commercial terms not established
Rate source ↗
Legacy customer deployment
Confirm the existing product/account agreement
Rate source ↗
Successor Modal deployment
Separate product and rate card
Do not assume legacy rates or allowances transfer automatically.
Rate source ↗

No current numeric legacy bill or savings percentage is inferred from an acquisition announcement. Compare the actual synchronization, orchestration, REPL, or runtime product, including migration and retained-data costs.

Check current Jamsocket pricing ↗

Sandbox0

$0.015/GiB-hour compute (billed by the second at approximately $0.000004167/GiB-second), plus $0.02/GiB-month of retained incremental RootFS and memory checkpoint data. Shared base images and platform recovery retention are excluded; paused sandboxes accrue storage charges only.

Compute / GiB-hour
$0.015
Retained data / GiB-month
$0.02
Paused compute
$0.00

A 4 GiB agent, 100 running hours

$6.00 compute

4 GiB × 100 hours, billed by the second. Keeping 20 GiB of billable incremental data for a full billing month adds $0.40. CPU is derived from memory by the platform; choose a tier that fits your workload.

Understand storage billing →

Before migrating from Jamsocket

  1. Identify the actual Jamsocket-family product, present service access, account terms, documents, Python state, files, and backend/orchestration dependencies.
  2. Export required artifacts and implement the required application protocols around a Sandbox0 runtime where appropriate.
  3. Validate equivalent application behavior separately from system persistence, RootFS growth, paused file access, and actual successor/legacy billing.

Common questions

Is Sandbox0 a drop-in Jamsocket replacement?

Evaluate API compatibility and product scope. These products serve different core workflows, so a change may require a different architecture.

Does keeping files also keep a running agent?

Filesystem state and volatile process state are separate. Sandbox0 requires explicit compatible memory checkpoints to preserve running processes; its default filesystem resume starts fresh processes.

Sources and review scope

The Boat team's Battleships directory is the discovery source. References below describe the product and plan discussed on this page. Check current availability, regional terms and billing units before migrating. Where the cited material does not establish a capability or price, the comparison identifies that uncertainty.

Battleships research record ↗modal.com/blog/jamsocket-is-joining-modal ↗jamsocket.com/ ↗Sandbox0 RootFS capacity →

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