What Is an API Gateway? An Enterprise Buyer's Guide (2026)

Large enterprises now manage an average of 1,800 APIs — but only 58% are formally documented or catalogued, according to Forrester research. 99% of enterprises encountered API-related security issues in the past year. And Gartner predicts that 40% of enterprise applications will include task-specific AI agents by 2026, up from less than 5% in 2025 — all of them calling APIs.

If your organisation exposes APIs to partners, internal teams, or AI tools, you already have an API management problem. Whether you've named it yet is a separate question.

An API gateway is the standard solution. But the enterprise API management market has grown fast — it reached $10 billion in 2025 — and not all gateways are built for regulated environments. This guide covers what an enterprise gateway actually does, what regulated enterprises specifically need, and what questions to ask before you buy.

What an API gateway does

An API gateway is a single entry point that sits between your clients — partner apps, internal services, AI tools — and your backend APIs. Every request passes through it before reaching your systems.

At its core, a gateway handles:

Routing — directing requests to the right backend service based on path, method, headers, or client identity
Authentication — verifying that the caller is who they say they are (API key, JWT, mTLS certificate)
Authorization — checking that the caller is allowed to perform the requested action on the requested resource
Rate limiting — preventing any single caller from overwhelming your backends, with limits configurable per partner or per API product
Logging and audit — recording what happened, when, and who did it, in a structured format that compliance teams can query

In practice, modern enterprise gateways do considerably more. Workflow automation, partner self-service developer portals, AI agent access, observability dashboards, and compliance reporting are now standard expectations — not premium add-ons.

Why enterprises can't use basic gateways

Consumer-facing API gateways prioritise speed to production. That is fine for a startup. It is a problem for a bank, a healthcare system, or a government agency.

The gaps show up in specific places:

Audit trails that satisfy regulators. 57% of organisations have experienced API-related breaches in the past two years, with 73% of those experiencing three or more incidents. When a breach happens — or when an auditor asks who accessed a specific endpoint on a specific date — you need a complete, structured audit trail tied to specific credentials, partners, and roles. Server logs are not an audit trail. A gateway that produces a queryable, tamper-evident record of every request and every configuration change is.

Per-partner access control. In open banking, healthcare interoperability, or B2B integrations, different partners are authorised for different APIs. A configuration error that gives Partner A visibility into Partner B's data is not a theoretical risk — it is the kind of incident that appears in regulatory filings. The gateway needs per-partner credential management baked in, not bolted on.

Role-based administration with separation of duties. Your platform team, compliance officer, and external auditor all need different levels of gateway access. The compliance team needs to query audit logs without being able to change routing rules. The auditor needs read-only access to records without exposure to credentials. Only 21% of organisations report high ability to detect attacks at the API layer — typically because access controls inside the gateway itself are too coarse.

Deployment that fits your compliance posture. Some regulated environments cannot put sensitive workloads in a public cloud. Air-gapped deployment is a requirement, not an option, for certain government, defence, and healthcare systems. A gateway that assumes cloud deployment is not evaluable for these environments.

A model for AI tools. Gartner found that more than 30% of the increase in API demand by 2026 will come from AI and LLM-based tools. The Postman 2025 State of the API Report found that 51% of organisations have already deployed AI agents, with 25% now designing APIs specifically with agents in mind. If your gateway does not have an access model for AI tools, those requests either get blocked or bypass your controls through workarounds. Neither outcome is acceptable for a regulated enterprise.

Core capabilities to evaluate

1. Access control and authentication

Look for: role-based access with separation of duties (view, edit, admin, audit roles), enterprise SSO via OIDC or SAML, token and certificate validation, IP allowlists, and per-partner credential management. Credentials should be encrypted at rest and ideally fetched from your own secrets manager — Vault, AWS Secrets Manager, or similar — rather than stored directly in gateway configuration.

The distinction between token validation and certificate validation matters for regulated industries. mTLS client certificates provide a higher assurance level than API keys for high-risk partner connections and AI agent authentication.

2. Audit trail and compliance logging

Every request — and every configuration change — should produce a structured log record with a consistent schema: who, what, when, which resource, what changed. The audit trail should be filterable by partner, API product, actor type, and time range. Compliance teams need a dedicated read-only audit role that lets them query records without access to routing configuration or credentials.

Note where those logs are stored. In cloud-managed gateways, audit logs often reside in the vendor's systems. For regulated industries, this means retention, access, and integrity guarantees all depend on the vendor's policies — not yours.

3. Developer portal

50% of organisations currently operate three or more API gateways, with fragmented developer-facing documentation scattered across teams. A good developer portal gives each partner their own scoped view: only the API products they are authorised to use, with passwordless sign-in, interactive try-it-in-browser testing, and spec downloads. Partners self-onboard without emailing your team. Support burden drops.

The scope constraint is the key compliance requirement: a partner's developer portal view must be filtered to their entitlements. A misconfiguration that exposes your full API catalogue to an external partner is a disclosure incident.

4. Workflow and routing logic

Modern gateways let you define routing logic, request transformation, conditional branching, and error handling visually. Custom code per partner or per API means a maintenance surface that grows with every integration and requires specialist knowledge to debug. Visual workflow configuration reduces both the time to build new integrations and the blast radius when something breaks.

5. AI agent access

AI agents need to call your APIs through the same gateway as everything else — with the same per-client access controls, rate limits, and audit records. A separate authentication path for AI tools creates a second compliance surface that most organisations are not equipped to govern. The gateway should log actor type — human, agent, copilot — so you can filter by it when producing compliance evidence.

65% of organisations believe generative AI poses serious-to-extreme risk to API security. The risk is manageable. It is not manageable if AI agents are calling APIs outside your governance perimeter.

6. Deployment flexibility

Verify whether the vendor supports on-premises deployment, hybrid configurations, and air-gapped environments — and what that actually means in practice. Some vendors offer "self-hosted" options that still require outbound connectivity for licensing checks or telemetry. In a regulated environment, any external data dependency at runtime needs to be assessed against your compliance requirements.

Ask specifically: what data leaves our environment during normal operation?

7. Observability

Real-time dashboards, structured logs, Prometheus-compatible metrics, and SIEM integration should be included without additional licensing. Metrics broken down by partner and API product — not just aggregate traffic — are what compliance and security operations teams actually need. A gateway that requires a separate observability tool to answer "which partner is generating the most errors right now?" is already adding sprawl.

The AI agent gap in most legacy gateways

This deserves its own section because it is where most legacy API management platforms have a concrete gap.

AI agents — whether built on MCP, direct API calls, or LLM orchestration frameworks — are not a future concern. They are already calling enterprise APIs in production. The Postman 2025 report found 51% of organisations have deployed them. Gartner's August 2025 prediction projects 40% of enterprise applications will include task-specific agents by year's end.

Legacy gateways were designed for human developers and application services. They have no concept of per-agent scope — the idea that one AI agent should be limited to read-only access on payment APIs while another has full access to identity APIs. They often have no actor type field in their audit logs, making it impossible to produce evidence of what AI agents specifically accessed.

A gateway purpose-built for 2026 treats AI agents as a first-class client type: scoped credentials, per-agent rate limits, audit records that distinguish agent calls from human calls, and a Copilot interface for operators to manage agent access in natural language.

Questions to ask any API gateway vendor

Before signing anything, get clear answers to these:

Where is our API traffic processed — on our infrastructure or yours?
What data leaves our environment during normal operation, including telemetry, license checks, and crash reports?
How does the audit trail work — what is logged, where is it stored, who can access it, and what is the retention model?
How is per-partner access enforced — can one partner ever access another partner's API products through misconfiguration?
What is your model for AI agent access — how do agents authenticate, how are they scoped, and how are their calls logged?
What does on-premises deployment look like — does it require any outbound connectivity at runtime?
What authentication protocols are supported for enterprise SSO?
Can we export our full configuration — routing rules, workflow definitions, partner credentials — in a standard format?

The last question matters more than most buyers realise. Vendor lock-in in API management accumulates in your configuration. Routing logic, workflow definitions, and partner entitlements stored in proprietary formats cannot be migrated without rebuilding from scratch.

What good looks like in 2026

A gateway built for regulated enterprises in 2026 handles all of these without requiring additional tools:

Apps, partners, and AI agents through the same entry point with identical governance
Full audit trail queryable by compliance teams directly — not through a vendor portal
Per-partner developer portal with scoped API catalogue access
On-premises, hybrid, or air-gapped deployment — your choice, same product
Visual workflow configuration without custom integration code
Observability included, not sold separately

50% of organisations currently run three or more gateways. That fragmentation compounds every compliance problem: multiple access control models, multiple audit trails, multiple update cycles, multiple things that can break simultaneously. If a vendor requires you to bolt on third-party tools to cover basic enterprise requirements, you're already managing sprawl before your first integration goes live.

Zerq is an enterprise API gateway built for regulated industries — banking, healthcare, fintech, and government. It runs on your infrastructure, stores audit data in your MongoDB instance, and handles apps, partners, and AI agents through one control plane.

See how it works → · Security & governance → · Request a demo →