DeepSeek's OpenAI-compatible chat schema accepts text content rather than OpenAI vision content parts, so forwarding Anthropic image blocks as image_url makes the upstream reject the request before the model can answer. Keep normal OpenAI Chat vision behavior as the default, but switch known DeepSeek-compatible chat proxy requests to a text-only conversion that preserves prompt text and replaces image payloads with a small omission marker.
Constraint: DeepSeek official Chat Completions docs list user message content as string text, while its Anthropic compatibility table marks image blocks as not supported.
Rejected: Expand unsupported-image error string matching only | it still surfaces the first turn as an API error and depends on provider wording.
Confidence: high
Scope-risk: narrow
Tested: bun test src/server/__tests__/proxy-transform.test.ts
Tested: bun test src/server/__tests__/providers.test.ts --test-name-pattern "handleProxyRequest|omits image_url"
Tested: bun test src/services/api/errors.test.ts tests/mediaRecoveryAndEstimation.test.ts
Tested: bun run check:server
DeepSeek-compatible OpenAI Chat providers require assistant reasoning_content to be replayed on later tool-call turns when thinking mode is active. The Anthropic-to-OpenAI chat transform now keeps that replay behavior behind an explicit compatibility option, and the proxy only enables it for DeepSeek/OpenCode base URLs so generic OpenAI-compatible providers keep their previous request shape.
Constraint: DeepSeek thinking mode rejects follow-up requests when prior assistant reasoning_content is omitted
Rejected: Trigger compatibility by model name | would affect unrelated OpenAI-compatible providers using DeepSeek model ids
Confidence: high
Scope-risk: narrow
Directive: Do not broaden this compatibility gate without proving other OpenAI-compatible providers accept these non-standard fields
Tested: Fixed-port Web UI harness with copied DeepSeek OpenAI Chat provider reproduced the 400 and passed through local proxy after the fix
Tested: bun test src/server/__tests__/proxy-transform.test.ts
Tested: bun run check:server
Tested: git diff --check
Not-tested: Direct OpenCode Go subscription endpoint, unavailable locally
Local OpenAI-compatible proxies can return function arguments as parsed objects instead of JSON strings. Preserve object-shaped arguments directly and serialize them for streaming deltas so Write, Bash, and Edit tool calls keep the fields required by Anthropic tool validation.
Constraint: Local proxy implementations such as OneAPI/NewAPI may not preserve OpenAI's string-only arguments shape.
Rejected: Normalize every upstream response through JSON.stringify before parsing | loses already-valid object identity and leaves streaming object deltas vulnerable to [object Object].
Confidence: high
Scope-risk: narrow
Directive: Do not assume function.arguments is always a string on provider responses or stream deltas.
Tested: bun test src/server/__tests__/proxy-streaming.test.ts src/server/__tests__/proxy-transform.test.ts
Tested: bun run check:server
Tested: bun run check:native
Tested: bun run quality:pr
Tested: agent-browser with real Ollama qwen3:4b provider for Write/Bash/Edit and streaming Write
Not-tested: Real Windows OneAPI/NewAPI instance from the issue reporters was not available locally.
Add a protocol-translating reverse proxy that allows using OpenAI-compatible
API providers (DeepSeek, OpenRouter, Groq, etc.) with Claude Code.
The proxy intercepts Anthropic Messages API requests from the CLI, transforms
them to OpenAI Chat Completions or Responses API format, forwards to the
upstream provider, and transforms streaming/non-streaming responses back.
Key features:
- Request transform: Anthropic Messages → OpenAI Chat/Responses
- Response transform: OpenAI → Anthropic (streaming SSE + non-streaming)
- Provider-agnostic reasoning support (reasoning_content, thinking_blocks,
reasoning fields from DeepSeek, OpenAI o-series, GLM-5, Groq, etc.)
- Event queue pattern for correct Anthropic SSE event ordering
- Two-step test: ① connectivity check ② full proxy pipeline validation
- Desktop UI: API format selector, two-step test results display
- License attribution for cc-switch (MIT, Jason Young)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
