CodeSandbox SDK

Executive Summary

Status note (June 2026): CodeSandbox SDK is active and being rebranded as Together Code Sandbox. Together AI now markets it as "Together Sandbox," and its docs state that features "are being migrated to the Together platform over the coming months." The npm package remains @codesandbox/sdk, and the SDK reached general availability in May 2025. Not deprecated — but expect the CodeSandbox brand to recede.

CodeSandbox SDK provides programmable microVM environments for AI agents with unique forking capabilities for A/B testing. Originally a browser-based IDE company founded in 2017, CodeSandbox was acquired by Together AI in December 2024 to power their Together Code Interpreter feature. Post-acquisition, Together expanded infrastructure capacity, cut credit pricing, and raised concurrency limits.

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Product Overview

CodeSandbox was founded in 2017 by Ives van Hoorne and Bas Buursma as a browser-based development environment. Over seven years, they built expertise in isolated code execution environments, eventually launching the SDK to let developers programmatically create and manage sandboxes.

In December 2024, Together AI acquired CodeSandbox to integrate their sandbox technology into the Together Inference Platform as the Together Code Interpreter. The SDK left beta and reached general availability in May 2025, and as of June 2026 it is actively maintained and marketed as Together Code Sandbox, with Together's docs noting features "are being migrated to the Together platform over the coming months." Customers Together showcases include HeroUI and LegionEdge.

Key Capabilities

Product Surfaces / Editions

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Technical Architecture

CodeSandbox uses microVMs for isolation, with 2.7-second cold starts (P95) from templates while maintaining security boundaries between sandboxes. Hibernated sandboxes resume in ~500ms and live VMs fork in under 1 second. The architecture supports persistent storage through git integration.

┌─────────────────────────────────────────┐
│       CodeSandbox SDK Platform          │
├─────────────────────────────────────────┤
│  ┌──────────┐  ┌──────────┐             │
│  │ Sandbox  │──│  Fork    │             │
│  │ (μVM)    │  │ (μVM)    │    ...      │
│  └────┬─────┘  └────┬─────┘             │
│       │             │                   │
│  ┌────┴─────────────┴─────┐             │
│  │   Snapshot Store       │             │
│  │   (Git-based)          │             │
│  └────────────────────────┘             │
│                                         │
│  ┌────────────────────────────────┐     │
│  │  Multi-Region microVMs         │     │
│  │  (US, APAC, EMEA)              │     │
│  └────────────────────────────────┘     │
└─────────────────────────────────────────┘

Key Technical Details

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Strengths

• Forking mechanism — Clone live sandboxes in under 1 second for A/B testing different agents
• Mature platform — 8+ years of experience building isolated code execution environments
• Together AI backing — Post-acquisition, Together expanded capacity, cut credit prices ~17%, and raised concurrency caps 2-2.5x
• Fast resume — Hibernated sandboxes restore in ~500ms with full state preserved
• Independent recognition — Northflank's 2026 sandbox roundup calls out CodeSandbox for "snapshotting and environment forking" and rates it well-suited for parallel agent runs
• Continuous context — Resume development in the same sandbox after inactivity
• Web development heritage — Particularly strong for frontend/web agent use cases; HeroUI cites 98% lower preview cold starts

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Cautions

• Brand transition underway — Together's docs say features "are being migrated to the Together platform over the coming months"; the CodeSandbox brand and standalone surfaces may not survive the migration
• Less AI-focused — Originally built for human developers, not specifically AI agents
• Slower cold starts — 2.7 seconds P95 vs 90-150ms for dedicated AI sandbox platforms
• Benchmark absence — Superagent's 2026 seven-provider sandbox benchmark (Modal, E2B, Daytona, Cloudflare, Vercel, Beam, Blaxel) omits CodeSandbox entirely, suggesting weaker mindshare among AI-native sandbox buyers
• Not open source — Proprietary platform; no self-hosting option
• Limited GPU support — No GPU access; ML workloads need Modal
• Smaller AI ecosystem — Fewer AI-specific integrations than E2B or Daytona

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What Developers Say

Independent community discussion is thin — the main public thread is the December 2024 Show HN launch, and post-acquisition commentary on Reddit and X is sparse.

• On the Show HN launch thread, willbdavenport flagged onboarding friction: "The details of how this works are somewhat confusing, might be nice to have a video tutorial here of a simple usecase"
• Vendor-hosted testimonials (treat accordingly): LegionEdge's founders say the platform saved them "at least 3 months of work" versus building their own VM system, and HeroUI reports "10% faster product development" and "98% lower preview cold starts"

The absence of substantial organic developer chatter — alongside CodeSandbox's omission from Superagent's 2026 benchmark — contrasts with the louder communities around E2B and Daytona.

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Pricing & Licensing

Usage rate: VM credits cost $0.01486 each (pay-as-you-go), with VM sizes consuming 5-320 credits/hour; minutes are the smallest billing unit.

Post-acquisition changes: Together cut the price-per-credit from $0.018 to $0.01486 and raised concurrent-VM caps 2x on Free (5 to 10) and 2.5x on Scale (100 to 250).

Licensing model: Proprietary, usage-based pricing; Together Code Interpreter is priced separately on the Together platform

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Competitive Positioning

Direct Competitors

When to Choose CodeSandbox SDK Over Alternatives

• Choose CodeSandbox SDK when: You need forking for A/B testing agents, or building web development agents
• Choose E2B when: You want AI-native infrastructure with larger ecosystem
• Choose Daytona when: You need Computer Use or fastest creation time
• Choose Runloop when: You're focused on coding agent benchmarking

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Ideal Customer Profile

Best fit:

• Teams already using CodeSandbox for development
• Web development agent use cases (frontend, full-stack)
• Organizations wanting forking for A/B testing agent approaches
• Together AI customers wanting integrated code interpretation
• Educational platforms needing isolated student environments

Poor fit:

• Teams needing fastest cold starts (E2B, Daytona faster)
• Security-critical workloads wanting open-source transparency
• GPU-required ML workloads (Modal better fit)
• Teams wanting self-hosted deployment

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Viability Assessment

The acquisition has played out as integration, not deprecation: as of June 2026 the SDK is GA, actively maintained, and cheaper than at acquisition, marketed as Together Code Sandbox while features migrate to the Together platform. The open question is whether CodeSandbox's web development heritage translates to AI agent use cases, where E2B and Daytona were built AI-native — and whether the standalone CodeSandbox surfaces survive the migration.

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Bottom Line

CodeSandbox SDK — now Together Code Sandbox — offers mature sandbox infrastructure with sub-second live-VM forking that enables A/B testing different agent approaches on identical environments. Eighteen months post-acquisition, Together AI has invested rather than shelved: the SDK is GA, credit prices fell 17%, and concurrency caps rose.

The trade-offs: CodeSandbox wasn't built AI-native, its 2.7s cold starts trail dedicated AI sandbox platforms, its AI-agent community presence is thin, and the brand itself is mid-migration into the Together platform.

Recommended for: Teams needing forking for A/B testing, building web development agents, or already using Together AI infrastructure.

Not recommended for: Teams needing fastest cold starts, open-source transparency, or GPU access — or those wary of buying a product mid-rebrand.

Outlook: Expect the CodeSandbox name to fade as Together Code Sandbox absorbs it over 2026. The microVM technology and @codesandbox/sdk package look durable; the standalone CodeSandbox surfaces (IDE, separate billing at codesandbox.io) are the parts most likely to change.

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Research by Ry Walker Research • methodology