Head to head · Checked against vendor sites, September 2026
Onyx Security vs Prompt Security (SentinelOne): AI agent security compared
The verdict
Onyx Security scores higher overall on our weights (7.4 vs 6.6 out of 10). Onyx Security scores higher on tool-call control, policy, identity and audit and breadth; Prompt Security scores higher on maturity. They tie on visibility and footprint. Neither publishes list prices.
Prompt Security (SentinelOne)
Owner: SentinelOne (acquisition announced 5 August 2025)
Best for SentinelOne customers
How do Onyx Security and Prompt Security compare on each criterion?
| Criterion | Weight | Onyx Security | Prompt Security | Edge |
|---|---|---|---|---|
| Visibility | 22% | 7 | 7 | Tie |
Why these scoresOnyx Security: Discovers AI agents across SaaS, cloud, endpoint and code; endpoint inventory detail is lighter than endpoint-first tools. Prompt Security: Inventories AI tools and code assistants, including shadow AI, and maps agents and MCP servers. | ||||
| Tool-call control | 20% | 8 | 6 | Onyx Security |
Why these scoresOnyx Security: Inspects every prompt, tool call and model response inline. Prompt Security: Governs what agents and MCP servers can do; per-tool-call enforcement is not detailed. | ||||
| Policy | 15% | 8 | 7 | Onyx Security |
Why these scoresOnyx Security: Five enforcement actions: alert, block, mask, steer, or ask a human. Prompt Security: Prevents prompt injection and data leakage for tools such as GitHub Copilot, Cursor and Claude Code. | ||||
| Identity and audit | 12% | 7 | 5 | Onyx Security |
Why these scoresOnyx Security: Agent identity and access governance is a named solution. Prompt Security: Agent vs human attribution not described on the pages we reviewed. | ||||
| Footprint | 13% | 6 | 6 | Tie |
Why these scoresOnyx Security: Works across endpoint agents, browser extensions, APIs and gateways; the endpoint component is a resident agent or extension. Prompt Security: Built into the SentinelOne Singularity Platform; the deployment method is not detailed. | ||||
| Breadth | 8% | 9 | 8 | Onyx Security |
Why these scoresOnyx Security: Browser AI, coding assistants, desktop agents, cloud workloads and MCP servers, plus agentic red teaming. Prompt Security: Employees, developers and homegrown AI apps from testing to runtime. | ||||
| Maturity | 10% | 7 | 8 | Prompt Security |
Why these scoresOnyx Security: $113M Series B announced 29 July 2026; SOC 2 Type II and ISO 27001 listed; pricing not published. Prompt Security: Backed by SentinelOne, which announced the acquisition on 5 August 2025; pricing not published. | ||||
| Total | 100% | 7.4 | 6.6 | Onyx Security |
How do they deploy, and what do they cost?
| Attribute | Onyx Security | Prompt Security |
|---|---|---|
| Owner | Not acquired | SentinelOne (acquisition announced 5 August 2025) |
| How it reaches devices | Endpoint agent, browser extension, API, gateway | Part of Singularity Platform; method not published |
| Deployment detail | Onyx says it needs no SDK changes and works across endpoint agents, browser extensions, APIs and gateways. It integrates with Okta, Entra, Splunk and CrowdStrike. On devices this means a resident component, which is why it scores lower on footprint than tools that deploy through EDR or MDM. | SentinelOne says Prompt Security deploys in minutes and is part of the Singularity Platform that protects endpoints, cloud, identity and data. The specific deployment method (browser extension, endpoint agent, IDE extension or proxy) is not detailed on the page we reviewed. |
| Pricing | Contact sales. Onyx Security does not publish pricing. | Contact sales. Pricing is not published. |
Source: onyx.security · Onyx AI security · Onyx Series B · SentinelOne Prompt Security page · SentinelOne press release, 5 August 2025 · prompt.security · Reviewed Sep 2026
Which should you choose?
Choose Onyx Security if
- Your priority matches our designation for Onyx Security: best for inline control across many AI surfaces.
- You need to evaluate or stop individual tool calls before they run: Onyx Security scores 8 to 6.
- You need an audit record that separates agent actions from human actions: Onyx Security scores 7 to 5.
Choose Prompt Security if
- Your priority matches our designation for Prompt Security: best for SentinelOne customers.
- Vendor maturity, public documentation and backing weigh heavily in procurement: Prompt Security scores 8 to 7.
Frequently asked questions
Which is better, Onyx Security or Prompt Security (SentinelOne)?
Onyx Security scores higher overall on our weights (7.4 vs 6.6 out of 10). Onyx Security scores higher on tool-call control, policy, identity and audit and breadth; Prompt Security scores higher on maturity. They tie on visibility and footprint. Scores are editorial assessments from public vendor material, reviewed September 2026.
Do Onyx Security and Prompt Security (SentinelOne) publish prices?
No. Neither publishes list prices, so ask both for a quote.
Do Onyx Security or Prompt Security (SentinelOne) replace EDR?
No. The tools in this guide add control over AI agent actions and work alongside EDR. Onyx Security: Endpoint agent, browser extension, API, gateway. Prompt Security: Part of Singularity Platform; method not published.
Related
Sources
- onyx.security · Reviewed Sep 2026
- Onyx AI security · Reviewed Sep 2026
- Onyx Series B · Reviewed Sep 2026
- SentinelOne Prompt Security page · Reviewed Sep 2026
- SentinelOne press release, 5 August 2025 · Reviewed Sep 2026
- prompt.security · Reviewed Sep 2026