Does the gateway support the Anthropic SDK's defaults?

The Anthropic SDK reads the base_url from configuration. Pointing it at the gateway URL changes the destination without changing any other line of code. The SDK's streaming, batching, and tool-use behaviors all work over the gateway.

How does the gateway handle prompt caching cost optimization?

Prompt caching at the Anthropic level continues to work over the gateway. The cache key Anthropic computes is based on the prefix content. The gateway forwards the prefix unchanged, so the cache hit rate stays the same as it would be in a direct connection. The gateway adds its own classification cache on the prefix to avoid re-classifying the same prefix on every request.

What happens to existing Anthropic rate-limit headers?

Anthropic returns rate-limit information in response headers. The gateway forwards those headers to the caller unchanged, so the application's rate-limit handling remains valid. The gateway can apply its own per-user or per-route limits on top, which the application's rate-limit handling can be made aware of via custom headers.

Can the gateway run policy on Claude's reasoning content?

The Anthropic API returns reasoning content as part of the response in models that emit it. The gateway treats reasoning content as response content for classification and policy purposes. Policy can permit, redact, or block reasoning content the same way it does for the user-facing response text.

Does the gateway work with the Anthropic vision capability?

The /v1/messages endpoint accepts image content blocks alongside text. The gateway extracts image bytes, runs a vision-capable classifier against them, and the policy evaluates the resulting labels alongside the text-side classification. The vision classifier is a deployer-chosen component; the gateway accommodates a deployer-supplied classifier or a default one.

The Anthropic API Gateway: Where the Inspection Point Sits Between Your Workforce and api.anthropic.com

An Anthropic API gateway is the inspection point HTTP traffic to api.anthropic.com passes through before it reaches Claude. The gateway attaches identity context the application supplies, runs prompt-level classification, evaluates the policy in effect at the moment of decision, and produces a per-decision audit record. The architecture sits between authenticated users or agents and the Anthropic API surface: the /v1/messages endpoint, the batch API, the files API, the computer-use beta, and the prompt-caching mechanism. Routing the application's base_url from https://api.anthropic.com to the gateway is a single configuration change.

I want to walk through the inspection points across each Anthropic API surface, how identity attaches on top of static Anthropic API keys, and how policy enforces against Claude-specific patterns like prompt caching and computer-use tool calls.

What the gateway intercepts

The gateway intercepts the HTTP request body, the headers, the streamed response, and any file uploads referenced by the request.

The Anthropic /v1/messages request body contains the messages array (the user and assistant turns), the system prompt block, the tools array (for tool use), and image content blocks the user attached. Prompt-level classification runs against the text content of the user turns and the system block. The image content blocks are extracted and classified through the vision-capable classifier, if the deployer has one configured.

The headers carry the Anthropic API key (x-api-key), the API version (anthropic-version), and any custom identity-bearing headers the application supplies. The gateway extracts the identity context from the application-supplied header, evaluates policy against it, and attaches the corporate identity to the per-decision record.

The response stream is the model's output, delivered as a sequence of message_delta and content_block_delta events. The gateway runs response-side classification against the streamed content and can block or redact specific blocks before they flow to the caller.

How Anthropic's API surfaces map to inspection points

The Anthropic API has three surfaces the gateway inspects.

The first is the /v1/messages endpoint, which is the primary completion surface. Each request is stateless: the application sends the full conversation history every call. Inspection runs against the full payload in one pass.

The second is the batch API (/v1/messages/batches). Batch requests submit many message payloads for asynchronous completion. The gateway inspects each batch item at submission time, applies policy per item, and writes the per-decision record for each. The asynchronous completion fires back through the same gateway URL, so the response side gets inspected on completion.

The third is the computer-use beta. The computer-use tool gives Claude an interactive surface that takes actions on a virtual computer (clicks, keystrokes, screenshots). The gateway treats the tool calls as part of the inspection scope: each computer_use tool invocation in the response is evaluated against policy. The policy can deny specific action categories (e.g. visit a specific URL, type credentials, take a screenshot of a sensitive screen).

How identity context attaches at the gateway

The Anthropic API key authenticates the application to Anthropic. The key does not authenticate the natural person or agent on whose behalf the application is calling Claude.

The gateway closes the gap the same way it does for any LLM provider. The Anthropic API key is held by the gateway, not passed through from the application. The application authenticates to the gateway with the corporate identity (SSO session, agent identity, role). The gateway authenticates to Anthropic with the team's API key. The decision record carries the corporate identity. The Anthropic billing reflects the team-level key.

The split satisfies NIST AI agent identity Pillar 1 (verified identity travels with the request) without changing the Anthropic billing structure.

Prompt caching and the inspection model

Anthropic's prompt caching reduces cost by reusing a cached prefix across multiple requests. The cached prefix is a portion of the system prompt or the user history that the application marks for caching via the cache_control field.

Inspection of cached prefixes runs once at cache creation and recurs on prefix invalidation. The gateway records the cached prefix's classification labels and reuses them on subsequent requests that hit the same cache. The record per decision still fires on every individual request, even when the prefix is cached: the cached prefix is part of the request context the decision was made against, and the record links to the cache entry.

This matters because the cached prefix can contain regulated content. If a cached system prompt includes customer-specific data or internal documentation, the cache entry inherits the same classification the live request would have produced. The gateway treats the cache entry as policy-evaluated content for the lifetime of the cache.

Computer-use tool policy

The computer-use tool gives Claude action capabilities outside the conversation. Each action Claude takes is a tool_use block in the response with parameters describing the action: a coordinate, a key sequence, a URL, a screenshot request.

Policy at the gateway evaluates each action:

The policy fires on the response side because the tool-use blocks are emitted by Claude as part of the response stream. The gateway buffers the block, runs policy against it, and either permits, redacts, or blocks before the block reaches the application that initiated the call.

Deployment trade-offs

The deployment patterns for the Anthropic gateway mirror the OpenAI gateway shapes: SaaS-hosted, VPC-isolated, sidecar.

The Anthropic-specific consideration is the streaming-response path. Anthropic's SSE event stream emits content blocks at high frequency, and the gateway needs low overhead on each event to avoid degrading the perceived response latency. The VPC-isolated deployment usually sits one network hop away from the application, which keeps the streaming overhead in the low-millisecond range.

The computer-use beta drives the sidecar pattern for some deployers. The buffering and classification work on screenshots is heavier than text inspection, and a sidecar shape keeps the work close to the calling application's compute budget.

Performance characteristics

Enforcement overhead on text completions measures under 50 ms per request in production tests on internal DeepInspect benchmarks. Streaming-response overhead adds milliseconds per event, dominated by the classifier inference cost on each emitted content block.

The end-to-end perception by the user matches the cached-prefix case from Anthropic's own performance documentation: the model dominates the timing, the gateway adds a small constant overhead, and the cache-hit cases shave the prompt-encode time off the critical path on both sides.

DeepInspect

This is the Anthropic API gateway DeepInspect was built to provide. DeepInspect sits inline between authenticated users or agents and any Anthropic endpoint. Every /v1/messages call, every batch submission, every computer-use action, and every streamed content block passes through one inspection point. Identity attaches at the request layer. Prompt and response classification fire at the boundary. Policy decides per request. The signed per-decision record commits before the response returns to the application.

The same inspection point sits in front of OpenAI, Azure OpenAI, Bedrock, Vertex, and self-hosted endpoints with the same policy and audit semantics. Anthropic is one entry point among several. The architecture stays the same.

If you are evaluating an Anthropic API gateway for a regulated deployment, book a demo today.