2026-09-18

Connect Claude Code to an Anthropic API Gateway

Connect Claude Code to an Anthropic API Gateway: a production guide with an explicit decision, reusable artifact, failure tests, operating signals, and source-qualified limits.

Choose the wire contract before the tool

Connect Claude Code to an Anthropic API Gateway should be implemented as a coding-agent integration contract, not as a one-off configuration. Freeze the protocol, ownership, evidence, and rollback condition before traffic moves. The concrete control points in this guide are ANTHROPIC_BASE_URL, ANTHROPIC_AUTH_TOKEN, Anthropic_Messages, model_aliases.

Connect Claude Code through a gateway that preserves the native Anthropic Messages contract. Set the base URL and authentication source explicitly, map primary and background model aliases deliberately, then verify streaming, tool use, usage, and failure behavior on the actual route. Do not treat an OpenAI-shaped compatibility response as proof.

Separate client setup from gateway policy

Separate the reader-facing task from the control-plane work behind it. Client setup owns the local file or environment variable; the gateway owns authentication, routing, limits, accounting, and attempt records; the provider owns its native protocol and volatile capability contract. A passing text prompt proves only that one path worked once.

A useful integration page owns protocol selection, configuration precedence, proof cases, and team rollout. The live setup document remains the owner of copy-paste installation steps. This division follows a capability-tree model: the article explains why and how to verify; the documentation supplies the current commands.

The owner record for this page is claude-code-anthropic-api-gateway; its frozen controls are ANTHROPIC_BASE_URL, ANTHROPIC_AUTH_TOKEN, Anthropic_Messages, model_aliases. Every value is reviewed at the wire or durable-state boundary and never inferred from a marketing label.

Compatibility contract: Connect Claude Code to an Anthropic API Gateway

Use the following review record as the deployable artifact. Technical values are intentionally explicit so a reviewer can compare configuration, wire evidence, and durable state without relying on a screenshot or a successful-looking outer response.

Control point	Fixed decision	Evidence to retain
`wire_contract`	`native_anthropic_messages`	`captured_messages_request + stream_events + stop_reason`
`base_url`	`reviewed_gateway_origin`	`ANTHROPIC_BASE_URL_effective_value_without_credentials`
`authentication`	`scoped_token_or_dynamic_helper`	`credential_source + owner + expiry + last_rotation`
`model_aliases`	`primary_and_background_mapped_explicitly`	`effective_alias_map + native_probe_per_alias`
`tool_use`	`tool_use_and_tool_result_correlated`	`tool_use_id + policy_decision + terminal_result`
`removal`	`original_environment_restorable`	`unset_or_restore_steps + direct_probe`

Reference configuration or flow

The example uses placeholders and deterministic inputs. Replace identifiers with reviewed values, never with credentials or customer content. Preserve the exact configuration snapshot alongside the probe result.

export ANTHROPIC_BASE_URL="https://modelflare.dev"
export ANTHROPIC_AUTH_TOKEN="<scoped-modelflare-key>"
export ANTHROPIC_MODEL="<reviewed-primary-alias>"
export ANTHROPIC_SMALL_FAST_MODEL="<reviewed-background-alias>"

Prove the complete coding-agent path

Run the ladder in order. A later check cannot compensate for a missing earlier boundary, and every attempt must remain attributable to one logical request.

Freeze the current client, gateway policy, model alias, route set, and observable baseline. Evidence record for wire_contract: enforce native_anthropic_messages and retain captured_messages_request + stream_events + stop_reason.
Run one deterministic positive probe and capture the client-visible response, request ID, selected route, terminal state, and usage. Evidence record for base_url: enforce reviewed_gateway_origin and retain ANTHROPIC_BASE_URL_effective_value_without_credentials.
Run the paired negative, limit, or disconnect case and verify that it fails in the intended layer. Evidence record for authentication: enforce scoped_token_or_dynamic_helper and retain credential_source + owner + expiry + last_rotation.
Repeat the probe through the actual protocol surface; do not infer native support from a neighboring compatibility endpoint. Evidence record for model_aliases: enforce primary_and_background_mapped_explicitly and retain effective_alias_map + native_probe_per_alias.
Roll out to a bounded cohort with an explicit owner, expiry time, stop threshold, and prepared rollback. Evidence record for tool_use: enforce tool_use_and_tool_result_correlated and retain tool_use_id + policy_decision + terminal_result.
Re-read durable configuration and accounting after the test, then remove temporary access or test data. Evidence record for removal: enforce original_environment_restorable and retain unset_or_restore_steps + direct_probe.

Integration failures that a text demo hides

Treat each item below as a release blocker. A 200 response, attractive dashboard, or single successful demo does not override these failure conditions.

protocol_emulation — Translating native Messages through an unverified OpenAI-compatible path can lose stop reasons, content blocks, or tool semantics.
auth_precedence_surprise — Multiple credential sources can cause Claude Code to use a different token than the reviewer expects.
background_model_gap — The main prompt can pass while background or lightweight work fails on an unmapped alias.
unbounded_shared_token — A static token shared across developers prevents precise revocation, quota, and attribution.

Rollout evidence and stop conditions

Monitor success and harm together. The threshold is a policy input, not a universal benchmark; choose it from the workload SLO and record the denominator before the observation window begins.

Signal	Decision threshold	Action
`native_messages_probe_rate`	`100%_for_each_required_alias`	`block_unverified_alias`
`tool_correlation_errors`	`0`	`disable_tool_use_and_rollback`
`credential_owner_coverage`	`100%`	`stop_new_onboarding`
`unexpected_direct_provider_calls`	`0`	`repair_environment_and_restart_client`

Modelflare boundary and limitations

Modelflare can centralize OpenAI-compatible and native-protocol routing, scoped keys, groups, usage records, and failure handling. A configured channel is not proof that every optional field, model alias, retention promise, region, or fallback is supported. Verify the selected route with its native protocol, preserve explicit zero values, and use the final durable settlement as billing truth.

Anthropic’s gateway documentation describes configuration principles and third-party examples; it does not endorse or certify Modelflare. Modelflare support must be proven through its current native Messages route and the exact model aliases selected for the workload.

Continue through the topic cluster

Use the linked parent for the broader decision, the sibling for the next implementation step, and the documentation route for current client configuration. These body links are deliberate because managed CMS articles do not currently carry a separate related-slug field.

Frequently asked questions

Why not use the OpenAI-compatible endpoint?

Claude Code expects Anthropic Messages semantics. Use the native route unless a complete translation contract has been independently proved.

Should the token be stored in a shell profile?

Prefer a scoped secret source or helper appropriate to the environment; never commit or print the token.

Why test the background alias?

Claude Code may use different models for foreground and background work, so the primary probe is incomplete by itself.

Sources and verification date

Sources were checked on 2026-08-07. They establish external contracts and engineering principles; they do not prove an untested route or future provider state.