Agent sandboxes / Tenki Sandbox alternative

A Tenki sandbox alternative for a persistent, growing agent computer

Tenki Sandbox is a full Linux VM product alongside Tenki’s CI runners and code reviewer. It already offers sticky long-running sessions and disk-plus-memory pause. Compare the sandbox-specific lifecycle and retained-storage model rather than using runner-minute prices.

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

When Tenki Sandbox fits

Tenki fits teams that want persistent agent sessions, full VM behavior, snapshot fan-out, templates, and integration beside its GitHub Actions infrastructure. Sticky sessions can run until explicitly terminated.

When to consider Sandbox0

Consider Sandbox0 when a per-user RootFS should grow automatically as files accumulate and remain accessible through supported file operations while compute is paused. Validate guest-kernel dependencies before porting from a full VM to gVisor.

Capabilities

Tenki Sandbox and Sandbox0: what persists?

Feature comparison with documentation and verification status
Environment and runtime lifetimeTenki SandboxA sticky session runs until terminated; it overrides a supplied maximum duration.View evidence ↗Sandbox0ttl 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 filesTenki SandboxPause retains the session disk; independent volumes survive termination.View evidence ↗Sandbox0The writable RootFS survives successful checkpoints, including software, system configuration, dependencies, and user data.Read documentation →
Whole RootFSTenki SandboxPause and snapshots capture the session VM disk as well as memory.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 stateTenki SandboxPause/resume restores the same session; snapshots seed new sessions.View evidence ↗Sandbox0Pause compute between tasks; resume on available capacity. Default resume starts fresh processes from the saved filesystem.Read documentation →
Memory and process stateTenki SandboxSnapshots and paused state include running processes and memory.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.

Tenki documents root-disk sizing at session creation, a 5 GiB service default, and explicit resize controls for separate volumes. Those are distinct from automatically growing the entire mounted root filesystem as free space runs low.

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 →

Sticky sessions deliberately override the duration cap

Tenki documents sticky as taking precedence over max duration, including when both are supplied. Sticky can be changed on a running session and survives manual pause. It supports long-lived execution until explicitly terminated; carry that policy into the orchestration and cleanup design.

Source 1 ↗

Snapshots retain memory; volumes outlive the VM

Tenki pause preserves disk and memory for the same session, while a snapshot can seed multiple sessions. A separate workspace volume survives session termination and must be attached explicitly, including after restore. These resources consume a shared retained-storage pool and have different cleanup requirements.

Source 1 ↗Source 2 ↗

Use sandbox meters and the intended billing term

Tenki’s CPU, memory, and running disk rates differ from its per-minute CI runner prices. Retained snapshots and volumes use workspace storage. Team’s headline monthly equivalent assumes yearly payment; its monthly-paid price is higher. Apply included credits before pricing usage.

Source 1 ↗

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.

Tenki Sandbox

Pricing reviewed 2026-10-18

Sandbox CPU
$0.000014 per vCPU-second
Rate source ↗
Sandbox RAM
$0.0000045 per GiB-second
Rate source ↗
Sandbox running disk
$0.00000003 per GiB-second
The rate card lists a 5 GiB free allowance; verify its scope for the account.
Rate source ↗
Retained workspace storage
$0.20 per GiB-month
From the first byte; snapshots, volumes, and runner caches share the pool.
Rate source ↗
Team plan, paid monthly
$250 per month
Alternatively $200 per month equivalent billed yearly; includes $100 monthly usage credit.
Rate source ↗

Starter has a $0 plan fee and limited initial credits; compute usage beyond included credit remains billable. Paused sessions stop compute and retain storage usage. Keep sandbox units separate from x64 and macOS runner minutes and code-review charges.

Check current Tenki Sandbox 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 Tenki Sandbox

  1. Record sticky and duration settings, root-disk size, paused state, snapshots, template images, and independently attached volumes.
  2. Export required files and port commands, process control, credentials, network allowlists, and preview endpoints; reattach external datasets deliberately.
  3. Test long unattended work, installed-package persistence, automatic RootFS growth, paused file operations, and active plus retained-storage cost.

Common questions

Is Sandbox0 a drop-in Tenki Sandbox replacement?

Evaluate API compatibility and product scope. A shared sandbox category does not make SDKs, lifecycle semantics, or limits interchangeable.

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 ↗tenki.cloud/docs/sandbox/sessions.md ↗tenki.cloud/docs/sandbox/concepts.md ↗tenki.cloud/docs/sandbox/volumes.md ↗tenki.cloud/docs/pricing.md ↗Sandbox0 RootFS capacity →

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