agentgateway v1.6.0: Cost Tracking With No Catalog Config

Originally published at webofmike.com on 2026-10-06. The demo repo and every command in it were run before publishing.

agentgateway v1.6.0 went GA on October 2. Two features are worth a hands-on look before anything else: a built-in LLM pricing catalog that gives you cost tracking with zero configuration, and per-key CEL rate limiting that buckets quota by any request attribute you pick. I ran both against a live gateway and a real Claude Sonnet 5 backend. Code and captured output are in themsquared/agw-16-hands-on.

Cost tracking used to mean declaring rates by hand

I wrote up agentgateway's per-API-key budgets back in v1.5.0: a budgets list per key, a limit in tokens or USD, and a 429 before the provider ever sees the request. That post also covered the gap underneath it. Budgets only work once the gateway knows what a token costs, and in 1.5 that meant a modelCatalog block naming every model and its per-million-token input and output rate, maintained by hand.

v1.6.0 replaces that with a model catalog agentgateway ships and maintains itself. The demo's entire LLM route config:

llm:
  port: 4000
  policies:
    localRateLimit:
    - type: requests
      maxTokens: 3
      tokensPerFill: 3
      fillInterval: 60s
      key: request.headers["x-api-key"]
  models:
  - name: claude
    provider: anthropic
    params:
      model: claude-sonnet-5
      apiKey: $ANTHROPIC_API_KEY

No modelCatalog anywhere. The access log still produces full cost data because claude-sonnet-5 is a model the built-in catalog already knows:

http.status=200 gen_ai.usage.input_tokens=8 gen_ai.usage.output_tokens=14
agw.ai.usage.cost.total=0.000156
cost.total=0.000156 cost.rate.input=2 cost.rate.output=10

cost.rate.input and cost.rate.output are USD per million tokens, pulled straight from the catalog. The math checks out: (8 * 2 + 14 * 10) / 1,000,000 = 0.000156. Nothing in the config told agentgateway what this model costs; it already knew.

Getting those fields into the access log in the first place is a frontendPolicies.accessLog.add block mapping CEL expressions to log keys:

frontendPolicies:
  accessLog:
    add:
      model.requested: llm.requestModel
      model.served: llm.responseModel
      tokens.input: llm.inputTokens
      tokens.output: llm.outputTokens
      cost.total: llm.cost.total
      cost.rate.input: llm.costRates.input
      cost.rate.output: llm.costRates.output

Those same CEL fields are what you'd read in a budgets policy from the 1.5 post, so this isn't a separate feature bolted on. It's the same cost-accounting plumbing, now backed by a catalog instead of a hand-maintained table.

Per-key rate limits need one rule, not one rule per key

The second feature in this run is localRateLimit, keyed by a CEL expression rather than a fixed value. The config above keys on request.headers["x-api-key"], with a 3-request bucket that refills every 60 seconds. One rule, evaluated per request, buckets independently per header value:

# key A, requests 1-3: all 200
http.status=200 ... cost.total=0.000156 ...
http.status=200 ...
http.status=200 ...

# key A, request 4, same minute
http.status=429 error="rate limit exceeded" reason=RateLimit

# key B, same minute, different header value
http.status=200 ... cost.total=0.000176

Key B never saw key A's limit. There's no second localRateLimit entry for it, no restart to pick up a new key. Any CEL expression over the request works as the bucket key, so this generalizes past API keys to things like a JWT claim or a source IP.

The gotcha: a 503 still spends a token

One run of the demo hit a transient upstream failure partway through:

http.status=503 error="upstream call failed: SendRequest: connection error: peer closed connection without sending TLS close_notify" reason=UpstreamFailure

x-ratelimit-remaining still dropped on that request. The call never reached Anthropic successfully, a 503 is the opposite of a billable response, but it still counted as one of the 3 admitted requests in the bucket. localRateLimit counts requests agentgateway admits, not requests that succeed upstream. If you're sizing maxTokens close to real traffic, budget headroom for upstream flakiness, because a bad backend day eats your quota exactly like a good one.

What this run doesn't cover

• No Kubernetes. v1.6.0's AgentgatewayModel CRD, now on by default in the Helm chart, and K8s-native session affinity are cluster-side features this standalone run doesn't exercise.
• One provider. The built-in catalog covers more than Anthropic; this demo only validates the provider with a key on hand.
• remoteRateLimit is a different policy, for quota shared across replicas. localRateLimit buckets live in the single proxy instance that created them, which is exactly what makes this demo's single-container setup representative of the behavior.

Run it yourself

Requirements: Docker and an ANTHROPIC_API_KEY. Tested on macOS (Apple silicon) against cr.agentgateway.dev/agentgateway:v1.6.0.

git clone https://github.com/themsquared/agw-16-hands-on.git
cd agw-16-hands-on
export ANTHROPIC_API_KEY=sk-ant-...
./run-demo.sh

To check the config against the v1.6.0 schema without sending any traffic:

docker run --rm -v "$PWD/config/config.yaml:/config/config.yaml:ro" \
  -e ANTHROPIC_API_KEY=dummy-for-validate \
  cr.agentgateway.dev/agentgateway:v1.6.0 -f /config/config.yaml --validate-only

Tear down with docker rm -f agw16-demo.

What changed, concretely

Going from v1.5.0 to v1.6.0, the same cost-and-quota problem from the per-key budgets post now needs less from you: no catalog to maintain, and a quota rule that keys itself by request content instead of being written once per key. The gotcha is the same shape either version: a limiter counts what it admits, not what succeeds, and that is worth checking against your own traffic patterns before you pick a maxTokens value. Repo and full captured output: themsquared/agw-16-hands-on.

Frequently asked questions

Does agentgateway v1.6.0 need a model catalog configured for cost tracking?

No. v1.6.0 ships a built-in model catalog, so a route to a known model like claude-sonnet-5 produces llm.cost.total and the input/output cost rates automatically, with no modelCatalog block anywhere in the config. Earlier versions required declaring rates by hand for every model in use.

How does agentgateway's per-key CEL rate limiting work?

A single localRateLimit policy keyed on an expression like request.headers[\

Does a failed upstream request still count against an agentgateway rate limit bucket?

Yes. A request that fails upstream, such as a dropped TLS connection, still consumes a token from the bucket. localRateLimit counts requests admitted at the gateway, not successful upstream responses, so a flaky backend can eat into a tight per-key quota without a single call completing.

Is agentgateway's remoteRateLimit the same as localRateLimit?

No. localRateLimit buckets live in memory on the single gateway instance that created them, which is exactly the single-container setup this demo runs. remoteRateLimit is a separate policy that shares one quota across replicas, which matters once more than one gateway instance sits behind a load balancer and you need one limit enforced across all of them.

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Canonical version, with machine-readable markdown at https://webofmike.com/agentgateway-v16-cost-tracking/index.md: https://webofmike.com/agentgateway-v16-cost-tracking/

Comments

[Ahmet Özel]

The 503 example makes the admission-versus-success distinction clear. I would derive the bucket key from an authenticated principal rather than trusting an arbitrary header value; otherwise a caller able to vary x-api-key could manufacture new buckets unless authentication validates that value first.

For cost logs, retaining the catalog version or effective rate timestamp would make historical totals reproducible after a gateway upgrade changes built-in prices. An unknown-model fixture is also useful: the log should distinguish an unavailable estimate from a genuine zero-cost response, especially if that estimate later drives a budget policy.