feat(providers): add anthropic-discount provider

[steebchen]

Summary

Adds a new anthropic-discount provider that behaves exactly like upstream Anthropic for all request/response handling, with two differences:

• Base URL + API key come from environment variables (LLM_ANTHROPIC_DISCOUNT_BASE_URL / LLM_ANTHROPIC_DISCOUNT_API_KEY), following the same stealth pattern as the avalanche provider.
• Pricing carries a 10% discount relative to upstream Anthropic.

Currently exposes a single model: Claude Opus 4.8 (anthropic-discount/claude-opus-4-8).

What changed

• packages/models: new anthropic-discount provider definition (env-based apiKey + baseUrl); claude-opus-4-8 gains an anthropic-discount provider mapping with all prices reduced by 10%.
• packages/actions: endpoint resolution reads LLM_ANTHROPIC_DISCOUNT_BASE_URL and appends /v1/messages; headers, request-body transform, and Anthropic message/cache-control handling treat anthropic-discount identically to anthropic.
• apps/gateway: every Anthropic-specific branch (content/reasoning/tool-call/token-usage extraction, streaming + non-streaming transforms, finish-reason mapping, response healing, effort/structured-output beta headers, temperature/top_p stripping, logs) now also matches anthropic-discount.
• .env.example: documents the two new env vars.

Token and base-URL resolution flow through the existing generic env machinery, so no per-provider plumbing was needed beyond the protocol branches.

Testing

• pnpm format ✅
• pnpm build ✅
• pnpm test:unit ✅ (1675 passed)

End-to-end verification against a real discounted endpoint is pending — the proxy will be run separately.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Added an "Anthropic (Discount)" provider option in provider/model selection; supports streaming, tool calls, reasoning extraction, and usage reporting like the standard Anthropic integration. Supports Anthropic beta features (effort and structured outputs) when enabled.
• Chores / Configuration
  • New environment settings to configure the discount endpoint: LLM_ANTHROPIC_DISCOUNT_BASE_URL and LLM_ANTHROPIC_DISCOUNT_API_KEY.
• Models
  • Discount provider enabled for supported Anthropic models (e.g., Claude Opus entries).

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

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Run ID: 92461d3f-7ff9-4671-b9a1-7abe495f9000

📥 Commits

Reviewing files that changed from the base of the PR and between 1c934b0 and d50f07e.

📒 Files selected for processing (4)

• apps/gateway/src/chat/chat.ts
• apps/gateway/src/chat/tools/transform-streaming-to-openai.ts
• packages/models/src/models/anthropic.ts
• packages/models/src/providers.ts

🚧 Files skipped from review as they are similar to previous changes (3)

• apps/gateway/src/chat/tools/transform-streaming-to-openai.ts
• packages/models/src/providers.ts
• apps/gateway/src/chat/chat.ts

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Walkthrough

This PR adds end-to-end support for a new anthropic-discount provider: provider registration and model entries, env var docs, base-URL resolution, header/context adjustments, request-body shaping (cache-control), and streaming/non-streaming response parsing and transformation mirroring Anthropic semantics.

Changes

Anthropic Discount Provider Support

Layer / File(s)	Summary
Provider registration and model configuration packages/models/src/providers.ts, packages/models/src/models/anthropic.ts, .env.example	New provider anthropic-discount is registered with required environment variables (LLM_ANTHROPIC_DISCOUNT_BASE_URL, LLM_ANTHROPIC_DISCOUNT_API_KEY), and provider entries are added for Claude Opus models.
Endpoint and base URL resolution packages/actions/src/get-provider-endpoint.ts	Base URL resolution reads LLM_ANTHROPIC_DISCOUNT_BASE_URL from environment and endpoint path routing treats anthropic-discount identically to anthropic.
Request context and headers packages/actions/src/get-provider-headers.ts, apps/gateway/src/chat/tools/resolve-provider-context.ts	Includes anthropic-discount in Anthropic-specific parameter handling (temperature/top_p) and anthropic-beta header injection (effort and structured-outputs) in streaming and non-streaming paths.
Request body and message transformation packages/actions/src/prepare-request-body.ts, packages/actions/src/transform-anthropic-messages.ts	Routes anthropic-discount through Anthropic-compatible request-body shaping and cache-control marker handling, reusing existing Anthropic message transformation logic.
Streaming response processing and enrichment apps/gateway/src/chat/chat.ts, apps/gateway/src/chat/tools/transform-streaming-to-openai.ts	Extends streaming flows to treat anthropic-discount like Anthropic for JSON-healing buffering, partial usage completion, tool-call enrichment/merge, content/reasoning extraction source selection, web-search accounting, and finish-reason parsing.
Response extraction and transformation utilities apps/gateway/src/chat/tools/*, apps/gateway/src/lib/logs.ts	Extraction and transformation utilities (content, reasoning, token usage, tool calls, provider response parsing, finish-reason mapping) now recognize anthropic-discount and reuse Anthropic-family logic.

Sequence Diagram

sequenceDiagram
  participant Client
  participant Gateway as Gateway
  participant ProviderTools as ProviderTools
  participant AnthropicDiscount as anthropic-discount

  Client->>Gateway: Chat request (provider: anthropic-discount)
  Gateway->>Gateway: resolveProviderContext (headers, beta markers)
  Gateway->>Gateway: prepareRequestBody (cache control, messages)
  Gateway->>AnthropicDiscount: POST /messages (streaming)
  AnthropicDiscount-->>Gateway: Streaming deltas (content/tool-calls/reasoning)
  Gateway->>Gateway: extractContent (from delta)
  Gateway->>Gateway: extractToolCalls (delta enrichment)
  Gateway->>Gateway: extractReasoning (from delta)
  Gateway->>Gateway: extractTokenUsage (from delta)
  Gateway->>ProviderTools: transformStreamingToOpenai
  Gateway->>ProviderTools: parseProviderResponse
  Gateway->>ProviderTools: mapFinishReasonToOpenai
  Gateway-->>Client: Transformed streaming response

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• theopenco/llmgateway#2435: Modifies packages/models/src/models/anthropic.ts provider configuration for Anthropic-family models (related to adding anthropic-discount).
• theopenco/llmgateway#2407: Touches Anthropic request-body/cache-control logic (prepareRequestBody / transformAnthropicMessages) overlapping with anthropic-discount cache-control behavior.
• theopenco/llmgateway#2178: Adds an Anthropic-compatible provider variant and adjusts gateway transformer/extractor switches (similar provider-dispatch changes).

Suggested reviewers

• smakosh

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The pull request title clearly and concisely describes the main change: adding a new anthropic-discount provider with proper feature scope prefix.
Docstring Coverage	✅ Passed	Docstring coverage is 85.71% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

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• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch anthropic-discount-provider

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[Copilot]

Pull request overview

Adds a new anthropic-discount provider that mirrors Anthropic's behavior but routes through a configurable endpoint (LLM_ANTHROPIC_DISCOUNT_BASE_URL / LLM_ANTHROPIC_DISCOUNT_API_KEY) and exposes Claude Opus 4.8 at 10% lower prices. The provider plugs into every Anthropic-specific code branch across model/provider definitions, request transforms, response/stream parsing, headers, finish-reason mapping, and logs.

Changes:

• Define anthropic-discount provider (env-based apiKey + baseUrl) and add a discounted Claude Opus 4.8 mapping.
• Endpoint resolution reads the discount base URL and reuses Anthropic's /v1/messages path.
• Group anthropic-discount with anthropic (and vertex-anthropic where applicable) across gateway request/response/streaming/header/finish-reason/log branches.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/models/src/providers.ts	Registers the new anthropic-discount provider with required env vars.
packages/models/src/models/anthropic.ts	Adds Claude Opus 4.8 mapping for anthropic-discount with 10% lower prices.
packages/actions/src/get-provider-endpoint.ts	Resolves discount base URL from env and routes to /v1/messages.
packages/actions/src/get-provider-headers.ts	Includes anthropic-discount in Anthropic header path (x-api-key + beta features).
packages/actions/src/prepare-request-body.ts	Treats anthropic-discount as Anthropic for cache-control and request-body transform.
packages/actions/src/transform-anthropic-messages.ts	Enables cache-control auto-injection for anthropic-discount.
apps/gateway/src/chat/tools/parse-provider-response.ts	Parses non-streaming responses identically to Anthropic.
apps/gateway/src/chat/tools/transform-streaming-to-openai.ts	Routes streaming chunks through the Anthropic transform.
apps/gateway/src/chat/tools/transform-response-to-openai.ts	Routes non-streaming responses through the Anthropic transform.
apps/gateway/src/chat/tools/extract-content.ts	Extracts streaming text content for anthropic-discount.
apps/gateway/src/chat/tools/extract-reasoning.ts	Extracts streaming reasoning for anthropic-discount.
apps/gateway/src/chat/tools/extract-tool-calls.ts	Extracts streaming tool-use blocks for anthropic-discount.
apps/gateway/src/chat/tools/extract-token-usage.ts	Reads Anthropic-style usage fields for anthropic-discount.
apps/gateway/src/chat/tools/map-finish-reason-to-openai.ts	Maps Anthropic finish reasons for anthropic-discount.
apps/gateway/src/chat/tools/resolve-provider-context.ts	Applies Anthropic temperature/top_p rule and beta headers to anthropic-discount.
apps/gateway/src/chat/chat.ts	Includes anthropic-discount in all Anthropic branches (headers, healing, streaming handling).
apps/gateway/src/lib/logs.ts	Unified finish-reason mapping covers anthropic-discount.
.env.example	Documents the new env vars.

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