Agent coordination / Agent Relay alternative

Agent Relay messaging alternative

Agent Relay connects agents through channels, direct messages, typed actions and reliable delivery into live sessions. Its durable messaging and searchable session history sit above the machines running those agents. For a returning agent computer, evaluate that machine’s filesystem lifecycle separately from the relay’s coordination state.

Start buildingCompare capabilities ↓

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

When Agent Relay fits

Agent Relay fits teams coordinating coding agents across laptops, servers and hosted tools, with shared conversations, events and session handoffs. Keep its communication layer when cross-agent delivery and collaboration are the requirement.

When to consider Sandbox0

Consider Sandbox0 when the required layer is the agent’s isolated Linux environment, including installed tools, system configuration and growing durable files. Messaging, multi-agent routing, history search and collaboration remain integrations you provide or retain.

Capabilities

Agent Relay and Sandbox0: what persists?

Feature comparison with documentation and verification status
Environment and runtime lifetimeAgent RelayAgent execution and lifetime depend on the chosen harness and host. Durable message delivery does not set one universal runtime allowance.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 filesAgent RelayDurable message/session records are documented; runtime disk retention belongs to the selected host/harness.View evidence ↗Sandbox0The writable RootFS survives successful checkpoints, including software, system configuration, dependencies, and user data.Read documentation →
Whole RootFSAgent RelayRelay’s session and delivery contract does not establish a managed whole writable RootFS lifecycle.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 stateAgent RelayConversation/session attachment is not an arbitrary-machine checkpoint 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 stateAgent RelayMessage replay and delivery acknowledgements are not process-memory snapshots.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.

Agent Relay’s durable messages and shared history are acknowledged. Disk geometry, installed tools and RootFS growth follow the actual agent host. Sandbox0 can supply that growing durable execution environment underneath a retained coordination layer.

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.

Relay history or queued messages can remain available while an agent is disconnected. That is useful coordination data; access to the agent host’s complete paused RootFS is a separate interface that the reviewed Relay contract does not establish.

See paused file operations →

Durable messages and live session delivery are distinct

The architecture guide stores a durable message record and routes deliveries through enrolled nodes/providers. Acknowledgements and per-agent sequence numbers support replay of unacknowledged messages after reconnect. Those are meaningful coordination guarantees; they do not establish recovery of the receiving machine’s entire filesystem or RAM.

Source 1 ↗

The harness owns the execution environment

The harness guide allows starting a CLI, attaching a terminal, connecting an app server, registering a browser or allocating a hosted worker. Relay does not have to own the process. Package installation, credentials, binaries and environment setup therefore depend on the chosen harness and host, rather than following one universal saved-machine contract.

Source 1 ↗

Cloud access and self-operated software need separate budgets

The current site offers a free start and an open-source relay you can run yourself. The reviewed pages do not publish a complete numeric paid rate card or resource allowance. Budget the hosting, agent/model accounts and any commercial relay terms separately; the same-name property-viewing product is outside this comparison.

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.

Agent Relay

Pricing reviewed 2026-10-18

Managed relay access
Free to start
Exact ongoing quotas and paid commercial rates are not established by the reviewed pages.
Rate source ↗
Self-operated relay
Software and operating terms apply
Your servers, agent hosts and model usage need their own budget.
Rate source ↗

Confirm cloud plan limits, retention and commercial terms for the particular Relay product you use. No hosted Linux CPU/RAM rate or model-token allowance is inferred from a free-start label. This page concerns the coding-agent messaging product on agentrelay.com, not a similarly named real-estate viewing service.

Check current Agent Relay 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 Agent Relay

  1. Inventory workspaces, agents, delivery nodes, harnesses, credentials, shared history and cloud/self-operated commercial terms.
  2. Retain the required messaging layer and port compatible agent execution to a Sandbox0 template with explicit host/lifecycle integration.
  3. Test delivery/reconnect behavior alongside system-tool retention, RootFS growth, paused files and the full host, relay and model bill.

Common questions

Is Sandbox0 a drop-in Agent Relay 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 ↗agentrelay.com/docs/markdown/architecture.md ↗agentrelay.com/docs/markdown/harnesses.md ↗agentrelay.com/ ↗agentrelay.com/docs/markdown/introduction.md ↗Sandbox0 RootFS capacity →

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