API compatibility

gpt2giga is a compatibility proxy, not a full clone of OpenAI, Anthropic, or Gemini. It focuses on the parts of the API that SDKs, editors, and agent tools usually need when the backend is GigaChat.

What does not work directly with GigaChat

Below are the practical incompatibilities that the proxy covers.

Client expectation	Why it breaks without the proxy	What gpt2giga does
OpenAI Chat Completions JSON	GigaChat has different formats for messages, tools, attachments, and responses.	Converts requests and responses, including streaming chunks.
OpenAI Responses API	GigaChat has no equivalent /responses route and schema for output items.	Accepts /responses, maps input/instructions/tools, and normalizes output items where possible.
Anthropic Messages API	Anthropic content blocks, tool use, system, max_tokens, and stream events do not match GigaChat.	Converts Anthropic payloads into GigaChat-compatible chat requests and maps the responses back.
Gemini GenerateContent API	Gemini contents/parts, candidates, function declarations, token counting, and SSE chunks differ from OpenAI/Anthropic and GigaChat.	Accepts Gemini-like requests at the root, under /v1, /v2, and /v1beta, translates them into normalized chat/embeddings requests, and maps the responses back into the Gemini shape.
SDK extra_headers, extra_query, extra_body	SDKs may send transport fields or optional model fields that GigaChat does not accept.	Filters dangerous headers, passes only allowed metadata, forwards GigaChat-specific extra_body, and ignores known unsupported optional fields.
Streaming SSE	OpenAI, Anthropic, and Gemini SDKs expect their own event names and delta shapes.	Generates OpenAI-, Anthropic-, and Gemini-compatible SSE from GigaChat streaming responses.
Tools and structured output	Function/tool schemas and JSON-schema controls differ between providers and backend modes.	Maps local tools/functions and provides a function-call fallback for structured output.
Authorization	OpenAI/Anthropic clients work with API keys, while GigaChat requires a different credentials/scope mechanism.	Separates proxy API-key authentication from upstream GigaChat authorization and, if needed, supports per-request pass-through.
Model discovery	GigaChat model responses do not match the OpenAI/Anthropic/Gemini/LiteLLM shape.	Repackages the model list and description for the target client.
OpenAI/Anthropic/Gemini batch routes	The installed GigaChat SDK/backend has no full create/list/retrieve/cancel flow for batch APIs.	Keeps the Files/Batches routers disabled until they can work end-to-end.

Mounted routes

Public API routes are available at the root and under versioned prefixes. The backend selection rule is the same for OpenAI-, Anthropic-, and Gemini-compatible routes: /v1 forces the GigaChat v1 contract, /v2 forces the GigaChat v2 contract, and root routes without a versioned prefix use GPT2GIGA_GIGACHAT_API_MODE=v1|v2.

Examples:

• /chat/completions, /v1/chat/completions, and /v2/chat/completions
• /responses, /v1/responses, and /v2/responses
• /messages, /v1/messages, and /v2/messages
• /models/{model}:generateContent, /v1/models/{model}:generateContent, /v2/models/{model}:generateContent, and /v1beta/models/{model}:generateContent

OpenAI-compatible routes

Route / group	Status	Comment
GET /models	Supported	List of GigaChat models in the OpenAI-compatible form.
GET /models/{model}	Supported	A single model in the OpenAI-compatible form.
POST /chat/completions	Supported	Non-streaming and streaming chat, tools/function calling, structured output, attachments where supported.
POST /responses	Supported	Maps Responses input/instructions/tools to GigaChat. GigaChat v2 mode provides a richer built-in-tool path.
POST /embeddings	Supported	Uses the model from the request or the proxy default for embeddings, depending on the configuration.
GET /model/info	Supported	LiteLLM-compatible model info endpoint.
POST /files, GET /files*	Disabled	Router code exists but is not mounted: files without batches give an incomplete OpenAI batch flow.
POST /batches, GET /batches*	Disabled	Disabled until batch create/list/retrieve/cancel appears in the GigaChat SDK/backend.
Stored chat-completion routes	Not implemented	Stored completions are out of scope for now.
Legacy POST /completions	Not implemented	Legacy text completions are out of scope for now.
Images, audio, moderations, uploads	Not implemented	The proxy does not implement these OpenAI route families.
Fine-tuning, assistants, threads, runs, vector stores	Not implemented	Out of scope for now.
Realtime/WebSocket API	Not implemented	Out of scope for now.

Anthropic-compatible routes

Route / group	Status	Comment
GET /models	Supported	Returned in the Anthropic shape when the request contains Anthropic SDK headers.
GET /models/{model_id}	Supported	Returned in the Anthropic shape when the request contains Anthropic SDK headers.
POST /messages	Supported	Messages API, streaming, local tools, GigaChat v2 mapping for compatible Anthropic provider tools, structured-output fallback.
POST /messages/count_tokens	Supported	Counts message, system, tool, and structured-output text through GigaChat token counting.
POST /messages/batches, GET /messages/batches*	Disabled	Router code exists but is not mounted until batch methods appear in the GigaChat SDK/backend.
Files API beta	Not implemented	Out of scope for now.
Skills API beta	Not implemented	Out of scope for now.
Agents, Sessions, Environments, Admin beta APIs	Not implemented	Out of scope for now.

Gemini-compatible routes

Gemini operation routes are mounted at the root, under /v1, /v2, and /v1beta, like the other public APIs. For clients that add the Gemini API version to an already versioned base URL, /v1/v1beta and /v2/v1beta are also available. /v1 and /v1/v1beta force the GigaChat v1 backend contract, /v2 and /v2/v1beta force the GigaChat v2 backend contract. The root Gemini paths /... and /v1beta/... without an outer /v1 or /v2 use GPT2GIGA_GIGACHAT_API_MODE=v1|v2.

Gemini model discovery in the pure Gemini form is always available under /v1beta, /v1/v1beta, and /v2/v1beta. On the shared /models, /v1/models, and /v2/models, the proxy keeps the OpenAI form by default, but returns the Gemini form for Google/Gemini clients, for example with the X-Goog-Api-Client or X-Goog-Api-Key headers, or with the ?key=... query parameter.

If proxy API-key authentication is enabled, Gemini-compatible clients can pass the key via x-goog-api-key or ?key=..., in addition to the common Authorization: Bearer ..., x-api-key, and ?x-api-key=.... For new setups, header-based authentication is preferable: query keys more often end up in access logs.

supportedGenerationMethods is built conservatively: known GigaChat/chat-like models advertise generateContent, streamGenerateContent, and countTokens; embedding-like models advertise only embedContent and batchEmbedContents; unknown/custom model ids advertise only countTokens, unless the backend metadata provides more precise information.

Route / group	Status	Comment
GET /v1beta/models, /v1/v1beta/models, /v2/v1beta/models	Supported	List of GigaChat models in the Gemini models/* form.
GET /v1beta/models/{model}, /v1/v1beta/models/{model}, /v2/v1beta/models/{model}	Supported	A single model in the Gemini Model form.
POST /models/{model}:generateContent, /v1/..., /v2/..., /v1beta/..., /v1/v1beta/..., /v2/v1beta/...	Supported	Gemini contents/parts, systemInstruction, generationConfig, function declarations, and multimodal parts are mapped to a normalized chat request.
POST /models/{model}:streamGenerateContent, /v1/..., /v2/..., /v1beta/..., /v1/v1beta/..., /v2/v1beta/...	Supported	Returns text/event-stream with Gemini GenerateContentResponse chunks.
POST /models/{model}:countTokens, /v1/..., /v2/..., /v1beta/..., /v1/v1beta/..., /v2/v1beta/...	Supported	Counts the text parts of contents/system/tools through GigaChat token counting.
POST /models/{model}:embedContent, /v1/..., /v2/..., /v1beta/..., /v1/v1beta/..., /v2/v1beta/...	Supported	Returns Gemini embedding.values using the GigaChat embeddings backend.
POST /models/{model}:batchEmbedContents, /v1/..., /v2/..., /v1beta/..., /v1/v1beta/..., /v2/v1beta/...	Supported	Returns Gemini embeddings[] using the GigaChat embeddings backend.
POST /v1beta/files, GET /v1beta/files*	Disabled	Router code is prepared but not mounted by default.
POST /v1beta/models/{model}:batchGenerateContent, GET /v1beta/batches*	Disabled	Router code is prepared but not mounted until end-to-end batch execution.

Gemini function calling

toolConfig.functionCallingConfig is mapped to the nearest supported semantics of the normalized/OpenAI-like layer:

• mode=AUTO keeps function calling optional. If allowedFunctionNames is set, the upstream receives only those declared functions.
• mode=NONE disables function calling.
• mode=ANY is supported only when, after applying allowedFunctionNames, exactly one function remains; it is mapped to a forced function call.
• mode=ANY without allowedFunctionNames is also supported if exactly one function is declared.
• mode=ANY with several possible functions returns 400, because the GigaChat backend path currently cannot honestly express "must call one of several functions."
• allowedFunctionNames is validated against the declared functionDeclarations; references to undeclared functions return 400.

Gemini embeddings

embedContent and batchEmbedContents support only text content.parts[].text. Empty requests, malformed batch entries, and non-text parts return 400 before the GigaChat embeddings backend is called.

outputDimensionality is accepted as compatibility metadata for the normalized request/observability, but is not passed upstream as an executable setting: the current GigaChat embeddings backend path does not provide controlled dimension reduction through this parameter.

Gemini release scope and validation

This is a Gemini-compatible API surface, not full Gemini API parity. Before a release, check exactly the declared scope:

• supported routes: generateContent, streamGenerateContent, countTokens, embedContent, batchEmbedContents, model discovery;
• supported prefixes: root, /v1, /v2, /v1beta, /v1/v1beta, /v2/v1beta;
• disabled routes: the Gemini Files API and batchGenerateContent routers exist in the code but are not publicly mounted until end-to-end upstream execution;
• partially supported fields: safetySettings and cachedContent are accepted for compatibility/diagnostics but not enforced; candidateCount, topK, and responseModalities are accepted/observed but ignored by GigaChat execution;
• structured output: generationConfig.responseMimeType=text/plain is treated as the default text mode, application/json is mapped to the JSON response format, and other MIME types and responseSchema without application/json return 400;
• unsupported features: Gemini tools outside the GigaChat SDK built-in mapping (fileSearch, googleMaps, computerUse, MCP, RAG/retrieval/Vertex tools), full multimodal/file-backed Gemini flows, non-text embeddings content;
• approximations: countTokens counts the extracted text through GigaChat token counting, ignores non-text/file/cachedContent parts, and is not an exact Gemini tokenizer.

Copyable release checklist for the PR description:

uv run ruff check .
uv run ruff format --check .
uv run pytest tests/test_protocol/test_gemini_adapter.py tests/test_router/test_gemini_router.py tests/integration/gemini/test_gemini_app_wiring.py

# Optional, requires live GigaChat credentials.
GPT2GIGA_RUN_LIVE_TESTS=1 uv run pytest tests/live/test_real_gigachat_integration.py -k gemini

# Optional release smoke for google-genai + Gemini CLI, auth on/off, and base URL matrix.
GPT2GIGA_RUN_GEMINI_SMOKE=1 GPT2GIGA_LIVE_ENV_FILE=.env.live uv run pytest tests/live/test_gemini_client_smoke.py

Compatibility policy

gpt2giga intentionally accepts many optional SDK fields that GigaChat cannot execute. This keeps clients from failing before the useful part of the request reaches the model.

Typical fields that are accepted and ignored:

• OpenAI metadata and fine-tuning parameters: user, metadata, service_tier, seed, prompt_cache_key, logprobs, top_logprobs, logit_bias, prediction, web_search_options, n > 1, parallel_tool_calls=true;
• Optional Anthropic fields: metadata, service_tier, top_k, container, context_management, mcp_servers, unsupported provider tools, citations, unsupported document/file content blocks. Compatible provider tools (web_search*, web_fetch*, code_execution*) are mapped to GigaChat v2 built-in tools unless GPT2GIGA_DISABLE_BUILTIN_TOOL_MAPPING=True.
• Optional Gemini fields: safetySettings, cachedContent, serviceTier, ignored generationConfig controls such as candidateCount/topK/responseModalities, and unsupported non-function tools are accepted and kept for diagnostics, but not applied by GigaChat. Compatible Gemini provider tools are mapped to GigaChat v2 built-in tools: googleSearch / googleSearchRetrieval -> web_search, urlContext -> url_content_extraction, codeExecution -> code_interpreter, unless GPT2GIGA_DISABLE_BUILTIN_TOOL_MAPPING=True; the full mapping is described in Built-in tools. Unsupported responseMimeType values and responseSchema without application/json are rejected.

If a field is intentionally ignored, it is not sent upstream as an executable GigaChat feature. A literal extra_body object can be passed to GigaChat additional_fields; in that case the GigaChat API determines support.

In observability, ignored request extensions are published in the redacted llm.request.extensions attribute, and ignored Gemini generation controls remain in llm.invocation_parameters.

A reference for each parameter: Client parameter compatibility.

The internal normalized layer that separates public protocol formats from provider execution is described in Normalized messages architecture.

Backend modes

By default, the GigaChat root compatibility methods are used:

GPT2GIGA_GIGACHAT_API_MODE=v1

Set GPT2GIGA_GIGACHAT_API_MODE=v2 so that root routes without /v1 or /v2 use the newer GigaChat v2/chat/completions surface for chat-like requests. For an explicit choice at the client level, use a base_url with /v1 or /v2: /v1 always goes to the GigaChat v1 contract, /v2 always goes to the GigaChat v2 contract.

/chat/completions remains a compatibility route and follows the env. The new built-in-tool capabilities evolve mostly around GigaChat v2 mode, so clients that need them can point to http://localhost:8090/v2.